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1.
We report herein catalytic asymmetric transformations of racemic α-borylmethyl-(E)-crotylboronate. The Brønsted acid-catalyzed kinetic resolution–allylboration reaction sequence of the racemic reagent gave (Z)-δ-hydroxymethyl-anti-homoallylic alcohols with high Z-selectivities and enantioselectivities upon oxidative workup. In parallel, enantioconvergent pathways were utilized to synthesize chiral nonracemic 1,5-diols and α,β-unsaturated aldehydes with excellent optical purity.We report herein catalytic asymmetric transformations of racemic α-borylmethyl-(E)-crotylboronate. 相似文献
2.
All carbon α-quaternary aldehydes are prepared via Co(iii)-catalysed sequential C–H bond addition to dienes and acetic formic anhydride, representing a rare example of intermolecular carboformylation. A wide range of internally substituted dienes containing diverse functionality can be employed in this reaction, affording complex α-quaternary aldehydes that would not be accessible via hydroformylation approaches. Mechanistic investigations, including control reactions and deuterium labeling studies, establish a catalytic cycle that accounts for formyl group introduction with an uncommon 1,3-addition selectivity to the conjugated diene. Investigations into the role of the uniquely effective additive Proton Sponge® were also conducted, leading to the observation of a putative, intermediate Co(i) tetramethylfulvene complex at low temperatures via NMR spectroscopy. The synthetic utility of the aldehyde products is demonstrated by various transformations, including proline-catalysed asymmetric aldol addition, reductive amination, and the asymmetric synthesis of amines using tert-butanesulfinamide technology.Co(iii)-catalysed sequential C–H bond addition to dienes and acetic formic anhydride results in a rare example of intermolecular carboformylation, generating versatile α-quaternary aldehyde products that are inaccessible via hydroformylation methods. 相似文献
3.
Chaoran Xu Jianglin Qiao Shunxi Dong Yuqiao Zhou Xiaohua Liu Xiaoming Feng 《Chemical science》2021,12(15):5458
Heterocycles have been widely used in organic synthesis, agrochemical, pharmaceutical and materials science industries. Catalytic three-component ylide formation/cycloaddition enables the assembly of complex heterocycles from simple starting materials in a highly efficient manner. However, asymmetric versions remain a yet-unsolved task. Here, we present a new bimetallic catalytic system for tackling this challenge. A combined system of Rh(ii) salt and chiral N,N′-dioxide–Sm(iii) complex was established for promoting the unprecedented tandem carbonyl ylide formation/asymmetric [4 + 3]-cycloaddition of aldehydes and α-diazoacetates with β,γ-unsaturated α-ketoesters smoothly, affording various chiral 4,5-dihydro-1,3-dioxepines in up to 97% yield, with 99% ee. The utility of the current method was demonstrated by conversion of products to optically active multi-substituted tetrahydrofuran derivatives. A possible reaction mechanism was provided to elucidate the origin of chiral induction based on experimental studies and X-ray structures of catalysts and products.Catalytic asymmetric tandem carbonyl ylide formation/[4 + 3]-cycloaddition of β,γ-unsaturated α-ketoesters, aldehydes and α-diazoacetates was achieved by using a bimetallic rhodium(ii)/chiral N,N′-dioxide–Sm(iii) complex catalyst. 相似文献
4.
Stereoselective Mannich reactions of aldehydes with ketimines provide chiral β-amino aldehydes that bear an α-tert-amine moiety. However, the structural variation of the ketimines is limited due to the formation of inseparable E/Z isomers, low reactivity, and other synthetic difficulties. In this study, a highly diastereodivergent synthesis of hitherto difficult-to-access β-amino aldehydes that bear a chiral α-tert-amine moiety was achieved using the amine-catalyzed Mannich reactions of aldehydes with less-activated Z-ketimines that bear both alkyl and alkynyl groups.Stereoselective Mannich reactions of aldehydes with ketimines provide chiral β-amino aldehydes that bear an α-tert-amine moiety. 相似文献
5.
Treatment of a BINOL-terpyridine compound with RuCl3 generates a Ru(II) complex (R)-6. This complex is found to be a novel multi-task catalyst capable of conducting a sequential oxidation and asymmetric alkyl addition to convert primary alcohols to chiral secondary alcohols. The terpyridine-Ru(II) site of (R)-6 catalyzes an efficient oxidation of primary alcohols to aldehydes which then undergo an enantioselective alkylation to generate chiral secondary alcohols when the BINOL site of (R)-6 is combined with ZnEt2 and Ti(OiPr)4. 相似文献
6.
Hiroyuki Kawai 《Journal of fluorine chemistry》2009,130(8):762-7806
Synthesis of novel C2-symmetric chiral crown ethers and their application to enantioselective trifluoromethylation of aldehydes and ketones are discussed. The use of a series of C2-symmetric chiral crown ethers 2 or 3 derived from commercially available (R)-1,1′-bi-2-naphthol for the enantioselective trifluoromethylation of 2-naphthyl aldehyde 1a with (trifluoromethyl)trimethylsilane in the presence of a base was attempted. Iodo-substituted crown ether 2b was found to be the most effective in the model reaction. Moderate enantioselectivities were observed for the trifluoromethylation of both aryl or alkyl aldehydes and alkyl aryl ketones in 21-44% ees. Although the ees are still improvable, this is the first example of a chiral crown ether-catalyzed enantioselective trifluoromethylation reaction. 相似文献
7.
A soluble chiral polymer ligand was synthesized by the polymerization of (R)-6,6′-dibutyl-3,3′-diformyl-2,2′-binaphthol (R-M-1) with 2,5-diaminopyridine (M-2) via a nucleophilic addition-elimination reaction. While arylboronic acids were used as the source of the transferable aryl group, the chiral polybinaphthols ligand in combination with Et2Zn without Ti(OiPr)4 exhibited higher enantioselectivity in asymmetric addition to aromatic aldehydes than alphatic aldehydes. When aromatic aldehydes with electron-withdrawing groups were chosen as substrates, the resulting diarylmethanols were produced in higher ee values than those with electron-donating groups as substrates. 2-Naphthaldehyde used as a substrate afforded product in 95% ee, which could be ascribed to the steric effect influence on this asymmetric arylation reaction. Moreover, the chiral polymer was easily recovered and reused, but exhibited a decrease of enantioselectivity in the third recycle. 相似文献
8.
Wei Wen Zhao-Pin Ai Chang-Lin Yang Chao-Xing Li Zhu-Lian Wu Tian Cai Qi-Xiang Guo 《Chemical science》2022,13(13):3796
Chiral α-amino ketones are common structural motifs in natural products and pharmaceuticals, as well as important synthons in organic synthesis. Thus, establishing efficient methods for preparing compounds with these privileged scaffolds is an important endeavor in synthetic chemistry. Herein we disclose a new catalytic asymmetric approach for the synthesis of chiral α-amino ketones through a chiral palladium-catalyzed arylation reaction of in situ generated challenging α-keto imines from previously unreported C-acyl N-sulfonyl-N,O-aminals, with arylboronic acids. The current reaction offers a straightforward approach to the asymmetric synthesis of acyclic α-amino ketones in a practical and highly stereocontrolled manner. Meanwhile, the multiple roles of the chiral Pd(ii) complex catalyst in the reaction were also reported.Chiral α-amino ketones are common structural motifs in natural products and pharmaceuticals, as well as important synthons in organic synthesis. 相似文献
9.
Yijing Dai Li Zheng Debarshi Chakraborty Babak Borhan William D. Wulff 《Chemical science》2021,12(37):12333
An effective catalyst has been developed for the three-component reaction of aldehydes, anilines and phosphites in an asymmetric catalytic Kabachnik–Fields reaction to give α-aminophosphonates. A catalyst was sought that would give high asymmetric inductions for aromatic and, and more particularly, for aliphatic aldehydes since there has not previously been an effective catalyst developed for this class of aldehydes. The optimal catalyst is prepared from three equivalents of the 7,7′-di-t-butylVANOL ligand, one equivalent of N-methylimidazole and one equivalent of zirconium tetraisopropoxide. This catalyst was most efficient in the presence of 10 mol% benzoic acid. Optimal conditions for aryl aldehydes required the use of 3,5-diisopropyl-2-hydroxyaniline and gave the aryl α-aminophosphonates in up to 96% yield and 98% ee over 11 different aryl aldehydes. The best aniline for aliphatic aldehydes was found to be 3-t-butyl-2-hydroxyaniline and gave the corresponding phosphonates in up to 83% yield and 97% ee over 18 examples. The asymmetric inductions for aliphatic aldehydes were comparable with those for aromatic aldehydes with a mean induction of 90% ee for the former and 91% ee for the latter. The best method for the liberation of the free amine from the aniline substituted α-aminophosphonates involved oxidation with N-iodosuccinimide.An effective catalyst has been developed for the three-component reaction of aldehydes, anilines and phosphites in an asymmetric catalytic Kabachnik–Fields reaction to give α-aminophosphonates. 相似文献
10.
An efficient palladium-catalyzed AAA reaction with a simple α-sulfonyl carbon anion as nucleophiles is presented for the first time. Allyl fluorides are used as superior precursors for the generation of π-allyl complexes that upon ionization liberate fluoride anions for activation of silylated nucleophiles. With the unique bidentate diamidophosphite ligand ligated palladium as catalyst, the in situ generated α-sulfonyl carbon anion was quickly captured by the allylic intermediates, affording a series of chiral homo-allylic sulfones with high efficiency and selectivity. This work provides a mild in situ desilylation strategy to reveal nucleophilic carbon centers that could be used to overcome the pKa limitation of “hard” nucleophiles in enantioselective transformations.A variety of “hard” α-sulfonyl carbanions of aryl, heteroaryl and alkyl sulfones were successfully employed as nucleophiles in palladium-catalyzed asymmetric allylic alkylation with excellent enantioselectivities. 相似文献
11.
This work describes the first preparation and application of primary trifluoroborate-iminiums (pTIMs) as a new, easily accessible and valuable class of organoboron derivatives. An array of structurally diverse pTIMs was prepared from potassium acyltrifluoroborates in excellent yields. Highly efficient and enantioselective [(R,R)-TethTsDpen-RuCl] complex-catalyzed hydrogenation of pTIMs provided direct access to chiral primary trifluoroborate-ammoniums (pTAMs). Moreover, facile synthesis of a series of structurally diverse chiral α-aminoboronic acids from chiral pTAMs was accomplished through novel, operationally simple and efficient conversion using hexamethyldisiloxane/aqueous HCl. Using no chromatography at any point, this work allowed easy access to chiral α-aminoboronic acids, as exemplified by the synthesis of optically pure anti-cancer drugs bortezomib and ixazomib.Starting with potassium acyltrifluoroborates (KATs), N-unprotected chiral α-aminoboronic acids are prepared in three simple steps without chromatography. This facile methodology will tap the broad potential of these valuable compounds. 相似文献
12.
Chiral bisphosphine ligands are of key importance in transition-metal-catalyzed asymmetric synthesis of optically active products. However, the transition metals typically used are scarce and expensive noble metals, while the synthetic routes to access chiral phosphine ligands are cumbersome and lengthy. To make homogeneous catalysis more sustainable, progress must be made on both fronts. Herein, we present the first catalytic asymmetric hydrophosphination of α,β-unsaturated phosphine oxides in the presence of a chiral complex of earth-abundant manganese(i). This catalytic system offers a short two-step, one-pot synthetic sequence to easily accessible and structurally tunable chiral 1,2-bisphosphines in high yields and enantiomeric excess. The resulting bidentate phosphine ligands were successfully used in asymmetric catalysis as part of earth-abundant metal based organometallic catalysts.Chiral bisphosphine ligands are of key importance in transition-metal-catalyzed asymmetric synthesis of optically active products. Mn(i)-catalyzed hydrophosphination offers a two-step, one-pot synthetic sequence to access chiral 1,2-bisphosphines.The vast majority of important catalytic transformations make use of very effective catalysts based on scarce, expensive and toxic noble transition metals and phosphine containing ligands that, especially when chiral, are often as expensive as the noble metals themselves due to their cumbersome synthetic accessibility.1 The past decade has witnessed significant progress towards the development of competitive catalysts that contain earth-abundant transition metals instead. These catalysts, however, still frequently rely on the use of chiral phosphine ligands. Bisphosphine ligands (Scheme 1A) for instance Pyrphos,2a Chiraphos,2b as well as Josiphos2c are among the most successful chiral ligands used in homogeneous catalysis. In recent years, bis(phosphine) monoxide compounds such as Bozphos,2d and Binap(o)2e have been shown to be powerful ligands in asymmetric catalysis as well. Unfortunately, the synthesis of these frequently and successfully used chiral phosphine-based ligands often requires stoichiometric amounts of chiral auxiliaries, enantiopure substrates, or separation by resolution to obtain them enantiomerically pure.1b–fOpen in a separate windowScheme 1(A) Examples of phosphine ligands commonly used in homogeneous catalysis. (B) Catalytic asymmetric hydrophosphination of various Michael acceptors. (C) This work: Mn (i)-catalyzed access to chiral 1,2-bisphosphines.Catalytic asymmetric hydrophosphination is one of the most straightforward approaches for generating optically active P-chiral or C-chiral phosphines, from which chiral ligands can be derived.3 The potential of hydrophosphination reactions to access enantioenriched chiral phosphines catalytically was demonstrated for the first time by Glueck and coworkers in 2001 using a catalytic system based on Pt and the chiral bisphosphine ligand Me-DuPhos.4 Following the publication of this initial work, precious noble metal complexes such as chiral Pd or Pt catalysts have been widely used in the field of asymmetric hydrophosphination (Scheme 1B).5 Only few examples utilizing earth-abundant metals such as Ni,6 Cu7 and very recently Mn8 have been reported to date for catalytic asymmetric hydrophosphination. Apart from metal based catalytic systems, examples of asymmetric organocatalytic hydrophosphination reactions were also presented in the literature.9 So far, all successful methods that rely on the addition of phosphines to α,β-unsaturated conjugated systems provide chiral monophosphines.3 Interestingly, the only reported example of catalytic hydrophosphination that allows access to chiral 1,2-bisphosphine ligands utilizes a Michael acceptor with a P-containing electron-withdrawing group.7bWhile α,β-unsaturated phosphine oxides are bench stable and readily available Michael acceptors, their application is less common when compared to conventional carbonyl based Michael acceptors, which is in part due to their lower reactivity.10 Yin and co-workers found an elegant solution to this problem by transforming α,β-unsaturated phosphine oxides into phosphine sulphides. This allows a ‘soft–soft’ interaction to be established between the Cu(i) atom of the chiral Cu(i)-catalyst and the S atom of the phosphine sulphide, enabling catalytic hydrophosphination towards the synthesis of chiral bisphosphines.7b While successful in applying this strategy for catalytic synthesis of variety of chiral bisphosphines, nevertheless it requires 6-steps synthetic sequence starting from α,β-unsaturated phosphine oxides (Scheme 1C).7bHerein, we present a highly efficient, short and scalable catalytic protocol for the synthesis of chiral 1,2-bisphosphines from readily available, bench stable α,β-unsaturated phosphine oxides employing Mn(i)-catalyzed hydrophosphination as its core transformation (Scheme 1D).The last five years witnessed remarkable success of Mn(i)-complexes as catalysts for reductive transformations of carbonyl compounds including asymmetric variants.11–13 Next to these reports, we have recently demonstrated that such complexes are capable of catalytic H–P bond activation of diarylphosphines.8 Based on these findings we hypothesised that Mn(i)-complexes should be able to bring the phosphine oxide and the phosphine reagents into closer proximity thus allowing the hydrophosphination reaction to take place directly with α,β-unsaturated phosphine oxides. This approach would avoid the additional synthetic steps and purifications procedures necessitated by the installation and removal of the sulphur atom that are intrinsic to the method utilising phosphine sulphides.At the outset of this work, bench-stable α-substituted α,β-unsaturated phosphine oxide 1a was chosen as the model substrate in the reaction with HPPh2 (i)-complex, Mn(i)-L, developed by Clark and co-workers13a,d for hydrogenation and transfer hydrogenation of carbonyl compounds, was selected as the chiral catalyst. After extensive optimization, the reaction with 5 mol% t-PentOK, 2.5 mol% Mn(i)-L, 1.05 equiv. of HPPh2 in toluene at room temperature for 16 hours was found to be optimal. Under these conditions, the product 3aa was obtained with 96% isolated yield and over 99% ee (entry 1).Optimization of the reaction conditionsa
Open in a separate windowaGeneral conditions: 1a (0.1 mol), Mn(i) (2.5 mol%), t-PentOK (5 mol%), 2a (0.105 mol) in toluene (1.0 ml) at rt for 16 h.bDetermined by 1H NMR of reaction crude.cDetermined by HPLC on a chiral stationary phase.dIsolated yield.In the absence of both the base and the catalyst, as well as in the presence of only Mn(i)-L, no reaction occurs at room temperature (entries 2 and 3). In the presence of only the base (5 mol% of t-PentOK), however, 99% conversion towards the phosphine product 3aa was observed (entry 4).14The screening of various solvents (entries 5–8) revealed excellent yields and enantiomeric ratios when using any of the following solvents: toluene, THF, and 1,4-dioxane. Given that the stereocenter in this reaction is generated upon formal stereospecific protonation, it was surprising that only a slight decrease in enantiomeric purity of the final product was observed in protic solvents, such as i-PrOH. On the other hand, running the reaction in MeOH led to a significant decrease in both substrate conversion and product ee.As for the nature of the base we discovered that alkoxides and Barton''s base provide the best results regarding the product yield and enantiopurity. The optimal performance of the base in the Mn(i)-catalyzed reaction is achieved with between 1.5 and 2 equivalents of the base with respect to the catalyst. A higher or lower amount of the base results in lower enantioselectivity or lower yield, respectively (compare entries 1, 11 and 12).With the optimized conditions in hand, we moved to explore the scope of this methodology, first concentrating on the R2 substituent on the phosphine oxide. Various substitutions with aryl or alkyl groups led to excellent results in all cases (Scheme 2). Substrates with either an electron-donating group (3ba and 3ca) or an electron-withdrawing group (3da, 3ea, and 3fa) at the para-position of the phenyl ring led to the corresponding products with over 98% ee. The phenyl and ester functional groups at the para-position were also well tolerated, providing products 3ga and 3ha with high yields and enantiopurities. Similar results were obtained for substrates containing methyl- (3ia), chloro- (3ja) or methoxy- (3ka) substituents at the meta-position of the phenyl ring.Open in a separate windowScheme 2Product scope of Mn(i)-catalyzed asymmetric hydrophosphination of α,β-unsaturated phosphine oxidesa.aReaction conditions: 0.1 M of 1 in toluene, Mn(i)-L (2.5 mol%), t-PentOK (5 mol%), HP(Ar)2 (1.05 equiv) at rt. Isolated yields reported. For products 3aa and 3za the absolute configurations were determined by transforming them into the corresponding known compounds 6aa and 6da and for the remainder of the products by analogy (for details see ESI†); b5 mol% Barton''s base used; c5 mol% Mn(i)-L,10 mol% t-PentOK used and reaction was carried out at rt for 72 h; d5 mol% Mn(i)-L,10 mol% t-PentOK used and reaction was carried out at rt for 5 days; e5 mol% Mn(i)-L,10 mol% t-PentOK used and reaction carried out at 60 °C; fthe reaction quenched with H2O2; gfor the absolute configuration of 3za, see the ESI.†α,β-Unsaturated phosphine oxides containing a heteroaryl moiety, such as 2-naphthyl (3ma), 3-thienyl (3na), and 3-pyridinyl (3oa), were well applicable in our catalytic system. We were pleased to see that substrate 3pa, bearing a ferrocenyl substituent – an essential structural component for many successful chiral ligands – can also be hydrophosphinated with excellent results. Next, α-alkyl substituted substrates were evaluated. The enantioselectivities observed for substrates with linear (3qa) and branched aliphatic substituents (3ra and 3sa) were in line with the results obtained for their aromatic counterparts. Substrates bearing functional groups amenable to further transformations, namely hydroxyl- (3ta), cyano- (3ua) or chloro-substituents provided the corresponding phosphine products with equally good results. We then move to study the effect of varying the substituents at the phosphorus atom. Various unsaturated diaryl phosphine oxides are compatible with this catalytic system and afford the corresponding products 3wa, 3xa, and 3ya with excellent enantiomeric excess and high isolated yield.The relatively less reactive β-butyl-substituted α,β-unsaturated phosphine oxide is well tolerated as well, providing the corresponding enantioenriched oxide product 3za with 87% ee. On the other hand, no conversion to the product 3a′a was observed with β-phenyl-substituted α,β-unsaturated phosphine oxide. Interestingly, this catalytic system also supports α,β-unsaturated phosphonates, generating the corresponding final products (4a′a, 4b′a, 4c′a, and 4d′a) with enantiomeric excesses in the range of 89–95%. The catalytic protocol was also applied to a phosphinate substrate, allowing access to the product 4e′a with two chiral centers (dr 1 : 1) with high ee. Finally, screening of various phosphine reagents revealed some limitations of the protocol. Hydrophopshination with (p-Me-C6H4)2PH and (p-MeO-C6H4)2PH led to the corresponding products 5ab and 5ac with good yields and good to excellent enantioselectivities. However, no conversion was obtained with the sterically more demanding (o-Me-C6H4)2PH, (3,5-CF3-C6H3)2PH, nor with Cy2PH and (p-CF3-C6H4)2PH. Attempts to access P-chiral phosphine product via addition of racemic diarylphosphine to α, β-unsaturated phosphine oxides led to the racemic P-chiral phosphine 5a′h.To demonstrate the potential application of our catalytic protocol in chiral phosphine ligand synthesis, we performed a gram-scale reaction between 1b and 2a (Scheme 3A). To our delight, the catalyst loading could be decreased to 0.5 mol%, leading to the product 3ba without deterioration of the yield (91%) or the enantioselectivity (98%).Open in a separate windowScheme 3(A) Gram-scale Mn(i)-catalyzed reaction using 0.5 mol% Mn(i)-L. (B) One-pot synthesis of chiral 1,2-bisphosphine boranes. (C) Synthesis of chiral 1,2-bisphosphines. (D) Application of bisphosphine 7ca in Cu(i)-catalyzed hydrophosphination.Building on these results, we then developed a highly efficient one-pot method for the synthesis of four different chiral phosphine boranes (6aa–6da) (Scheme 3B) that yield the corresponding chiral 1,2-bisphosphine ligands (7aa–7da) in a single deprotection step (Scheme 3C). As is typical of any phosphines, the 1,2-bisphosphines 7 prepared in this study can easily oxidize during chromatographic purifications.7bTherefore, to minimise chromatographic purification, as well as to facilitate product separation, degassed water was used to wash the reaction mixture, followed by the removal of volatiles under high vacuum. The free ligands 7 were obtained in good yields and high purity. Importantly, the 1,2-bisphosphine 7aa is a known, efficient chiral ligand for Rh-catalyzed asymmetric hydrogenation of α-amino-α,β-unsaturated esters.7b We also examined our bisphosphine ligand 7ca in the Cu-catalyzed hydrophosphination of α,β-unsaturated phosphine oxide 1a (Scheme 3D), obtaining the desired product 3aa in good yield (90%) and high enantioselectivity (92%). Similarly, α,β-unsaturated carboxamide 8 was investigated,7c providing the corresponding product 9 in good yield (82%) and moderate ee (52%).From a mechanistic point of view, we wondered whether our base activated Mn-catalyst I is involved in the activation of the phosphine reagent 2avia ligand–metal cooperation, as proposed in our previous work on α,β-unsaturated nitriles,8 or whether it also plays a role in the activation of the phosphine oxide substrate 1. Preliminary NMR spectroscopic studies did not reveal any interaction between I and 1 (see ESI†) leading us to hypothesise that the current transformation might follow a mechanistic path that primarily involves phosphine activation, as depicted in Scheme 4. Additional interaction between the NH and P O moieties of the catalyst and phosphine oxide respectively is also possible and cannot be excluded at this stage. Detailed mechanistic studies are currently underway.Open in a separate windowScheme 4Hypothetical catalytic cycle.In summary, we have developed the first manganese(i) catalyzed enantioselective strategy for the hydrophosphination of α, β-unsaturated phosphine oxides. This methodology allows a high-yielding, catalytic, two-step sequence for the synthesis of enantiopure chiral 1,2-bisphosphine ligands, that were successfully applied in asymmetric catalysis. Since manganese is the third most abundant transition metal in the Earth''s crust, a general catalytic method to access chiral bisphosphine ligands using this metal is further step towards more sustainable homogeneous catalysis. Further work is currently underway in order to unravel the mechanism of this transformation. 相似文献
Entry | Deviation standard conditions | Conv.b (%) | Eec (%) |
---|---|---|---|
1 | None | >99 (96)d | >99 |
2 | Without Mn(i)-L and t-PentOK | 0 | — |
3 | Without t-PentOK | 0 | — |
4 | Without Mn(i)-L | 99 | — |
5 | THF instead of toluene | 99 | 96 |
6 | 1,4-Dioxane instead of toluene | 98 | 97 |
7 | i-PrOH instead of toluene | 75 | 95 |
8 | MeOH instead of toluene | 90 | 52 |
9 | t-BuOK instead of t-PentOK | 99 | 97 |
10 | Barton''s base instead of t-PentOK | 98 | 98 |
11 | t-PentOK (2.5 mmol%) | 56 | 99 |
12 | t-PentOK (7.5 mmol%) | 99 | 95 |
13.
Suresh Rajamanickam Mayank Saraswat Sugumar Venkataramani Bhisma K. Patel 《Chemical science》2021,12(46):15318
An intermolecular radical based distal selectivity in appended alkyl chains has been developed. The selectivity is maximum when the distal carbon is γ to the appended group and decreases by moving from γ → δ → ε positions. In –COO– linked alkyl chains, the same distal γ-selectivity is observed irrespective of its origin, either from the alkyl carboxy acid or alkyl alcohol. The appended groups include esters, N–H protected amines, phthaloyl, sulfone, sulfinimide, nitrile, phosphite, phosphate and borate esters. In borate esters, boron serves as a traceless directing group, which is hitherto unprecedented for any remote Csp3–H functionalization. The selectivity order follows the trend: 3° benzylic > 2° benzylic > 3° tertiary > α to keto > distal methylene (γ > δ > ε). Computations predicted the radical stability (thermodynamic factors) and the kinetic barriers as the factors responsible for such trends. Remarkably, this strategy eludes any designer catalysts, and the selectivity is due to the intrinsic substrate reactivity.An intermolecular amination at the distal methylene carbon has been realized in an appended alkyl chain with electron withdrawing groups. Traceless remote Csp3–H functionalization has been accomplished using borate esters. 相似文献
14.
Taichi Kano 《Tetrahedron》2007,63(35):8658-8664
A 1,4-addition of alcohols to α,β-unsaturated aldehydes was found to be efficiently promoted by biphenyldiamine-based catalyst 3 without formation of the acetals. An asymmetric variant of this reaction has also been performed by designing a novel axially chiral organocatalyst (R)-10c. 相似文献
15.
Disclosed here is a catalytic asymmetric azidation reaction for the efficient synthesis of α-azido ketones bearing a labile tertiary stereocenter. With a superb chiral squaramide catalyst, a mild asymmetric formal H–N3 insertion of α-carbonyl sulfoxonium ylides proceeded with excellent efficiency and enantioselectivity. This organocatalytic process not only complements the previous α-azidation approaches for the formation of quaternary stereocenters and mostly for 1,3-dicarbonyl compounds, but also has advantages over the well-known metal-catalyzed asymmetric carbene insertion chemistry using α-diazocarbonyl compounds. Detailed mechanistic studies via control reactions and NMR studies provided important insights into the reaction pathway, which features reversible protonation and dynamic kinetic resolution. The curiosity in mechanism also led to the development of a simplified alternative protocol with a cheaper HN3 source.An organocatalytic asymmetric H–N3 insertion of α-carbonyl sulfoxonium ylides has been developed, providing efficient access to α-azido ketones bearing labile tertiary stereocenters and complementing the metal carbene insertion chemistry. 相似文献
16.
Co(ii)-based metalloradical catalysis has, for the first time, been successfully applied for asymmetric intramolecular C–H alkylation of acceptor/acceptor-substituted diazo reagents. Through the design and synthesis of a new D
2-symmetric chiral amidoporphyrin as the supporting ligand, the Co(ii)-based metalloradical system, which operates at room temperature, is capable of 1,5-C–H alkylation of α-methoxycarbonyl-α-diazosulfones with a broad range of electronic properties, providing the 5-membered sulfolane derivatives in high yields with excellent diastereoselectivities and enantioselectivities. In addition to complete chemoselectivity toward allylic and allenic C–H bonds, the Co(ii)-based metalloradical catalysis for asymmetric C–H alkylation features a remarkable degree of functional group tolerance. 相似文献
17.
Masaaki Omote 《Tetrahedron》2006,62(8):1886-1894
Axially dissymmetric ligands with perfluoroalkyl groups, (Ra)-2,2′-bis[(R)-1-hydroxy-1H-perfluorooctyl]biphenyl [(Ra)-(R)2-1c] and its enantiomer, have been synthesized successfully by the coupling reaction of the corresponding aryl bromide using Ni(COD)2. These ligands showed much higher asymmetric induction in the reaction of various aldehydes with diethylzinc than the trifluoromethyl (1a) or pentafluoroethyl (1b) analogues. Furthermore, 1c was recovered quantitatively by extraction with a fluorous solvent from the reaction mixture due to its high fluorine content. The recovered ligand 1c was pure enough to be reused without purification. The efficiency of 1c as the chiral ligand was not decreased at all even after seven times recycling. 相似文献
18.
(Ra)-(R)2-2,2′-Bis(1-hydroxy-1H-perfluorooctyl)biphenyl ((Ra)-(R)2-1c), which is an axially dissymmetric ligand with two chiral centers, works as a good chiral auxiliary for asymmetric aldol reaction. Thus, the reaction of monopropanoyl ester of 1c (2) with benzaldehyde in the presence of triethylamine and titanium(IV) chloride gave (2R),(3S)- and (2R),(3R)-3-hydroxy-2-methyl-3-phenylpropanoic acid esters (3a) in an approximate ratio of 4:1 in a total high yield. This result shows that stereoselectivity at 2-position is quite high, while that at 3-position is moderate. Both isomers were easily separated by column chromatography. Methanolysis of the separated isomers gave nearly quantitative recovery of 1c by extraction with a fluorous solvent without any loss of ee, while methyl (2R),(3S)- or (2R),(3R)-3-hydroxy-2-methyl-3-phenylpropanoates were obtained by CH2Cl2 extraction quantitatively in >99% ee. Aldol reaction of 2 with various aldehydes gave similar results. 相似文献
19.
Fu-Sheng He Chun Zhang Minghui Jiang Lujun Lou Jie Wu Shengqing Ye 《Chemical science》2022,13(30):8834
An organocatalytic enantioselective radical reaction of potassium alkyltrifluoroborates, DABCO·(SO2)2 and α,β-unsaturated carbonyl compounds under photoinduced conditions is developed, which provides an efficient pathway for the synthesis of chiral β-sulfonyl carbonyl compounds in good yields with excellent enantioselectivity (up to 96% ee). Aside from α,β-unsaturated carbonyl compounds with auxiliary groups, common chalcone substrates are also well compatible with this organocatalytic system. This method proceeds through an organocatalytic enantioselective radical sulfonylation under photoinduced conditions, and represents a rare example of asymmetric transformation involving sulfur dioxide insertion.A photoinduced organocatalytic enantioselective radical reaction is developed, affording chiral β-sulfonyl carbonyl compounds in good yields with excellent enantioselectivity (up to 96% ee). 相似文献
20.
Lan He 《Tetrahedron》2005,61(35):8505-8511
This paper described an efficient synthetic strategy for chiral acyclic nucleoside analogues containing both the phenoxy components of some bioactive natural compounds and a heterocyclic base. The phenoxy components with adenine moiety were incorporated into the chiral acyclic nucleoside analogues through two key synthetic tactics. Chiron 5-(R)-menthyloxy-2(5H)-furanone 5 was obtained in good yield from the cheap starting material furfural via a valuable synthetic route. The asymmetric Michael addition of 5 with adenine and the subsequent reduction reaction afforded the key chiral intermediate, 2-(R)-(9′-adeninyl)-1,4-butanediol 8. The absolute configuration of 8 was established by X-ray crystallography. The intermolecular dehydration reaction between 2-(9′-adeninyl)-1,4-butanediol 8 and phenoxy components 9 on treatment with diethyl azodicarboxylate and triphenylphosphine was carried out to give the chiral acyclic nucleoside analogues 1a-1e. The regioselectivity of the reaction was established by NMR methods, especially through 13C NMR shifts and NOE effect observed in the target molecule 1c, as well as by HMBC/HMQC experiments. The target compounds were tested for inhibition of cytopathogenicity against different cancer cells and exhibited potential anticancer activity. 相似文献