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1.
A new catalytic retro‐pinacol/cross‐pinacol reaction, followed by subsequent rearrangement or deoxygenation of the intermediately formed vicinal diols, is described. This operationally simple one‐pot protocol allows isolation of geminal α,α‐diphenyl ketones or 1,1‐diphenyl alkenes with high yields and selectivities. 相似文献
2.
Gowravaram Sabitha Arekuti Maheswara Reddy Singam Siva Sankara Reddy Jhillu Singh Yadav 《Helvetica chimica acta》2013,96(8):1610-1615
Stereoselective syntheses of (?)‐(1R,1′R,5′R,7′R)‐1‐hydroxy‐exo‐brevicomin ( 1 ) and (+)‐exo‐brevicomin ( 2 ) were accomplished from 3,4,6‐tri‐O‐acetyl‐D ‐glucal ( 5 ; Schemes 2 and 3). Chemoselective reduction, Grignard reaction, Barton? McCombie deoxygenation, and ketalization were used as key steps. 相似文献
3.
An efficient method for the selective hydrogenation of a series of α,β-epoxyketones to β-hydroxyketones using catalytic amount of two sulfinyl analogues of NAD^+ model compounds is reported. The lack of any diastereoselectivity for the formation of β-hydroxyketones with optically pure sulfinyl analogue of NAD^+ model supports the radical mechanism proposed previously. 相似文献
4.
Two natural diarylheptanoids, 2‐benzyl‐5‐(2‐phenylethyl)furan ( 1 ) and 2‐methoxy‐4‐{[5‐(2‐phenylethyl)furan‐2‐yl]methyl}phenol ( 2 ), were synthesized starting from 2‐furaldehyde. A Wittig reaction of 2‐furaldehyde with benzyltriphenylphosphonium bromide followed by reduction of the alkene C?C bond with Mg gave 2‐(2‐phenylethyl)furan ( 5 ). Lithiation of 5 with BuLi at ?78° followed by alkylation with benzyl bromide gave natural product 1 . In another approach, Friedel? Crafts acylation of compound 5 with benzoyl chloride followed by deoxygenation of the C?O group afforded 1 . The natural product 2 was also synthesized by acylation of 5 with 4‐acetoxy‐3‐methoxybenzoyl chloride ( 16 ) followed by deoxygenation and deacetylation. 相似文献
5.
This contribution reports an unprecedentedly efficient dimerization and the first successful polymerization of lignocellulose‐based β‐angelica lactone (β‐AL) by utilizing a selective Lewis pair (LP) catalytic system, thereby establishing a versatile bio‐refinery platform wherein two products, including a dimer for high‐quality gasoline‐like biofuel (C8–C9 branched alkanes, yield=87 %) and a heat‐ and solvent‐resistant acrylic bioplastic (Mn up to 26.0 kg mol?1), can be synthesized from one feedstock by one catalytic system. The underlying reason for exquisite selectivity of the LP catalytic system toward dimerization and polymerization was explored mechanistically. 相似文献
6.
Asymmetric Desymmetrization via Metal‐Free C−F Bond Activation: Synthesis of 3,5‐Diaryl‐5‐fluoromethyloxazolidin‐2‐ones with Quaternary Carbon Centers
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Junki Tanaka Satoru Suzuki Etsuko Tokunaga Prof. Dr. Günter Haufe Prof. Dr. Norio Shibata 《Angewandte Chemie (International ed. in English)》2016,55(32):9432-9436
We disclose the first asymmetric activation of a non‐activated aliphatic C?F bond in which a conceptually new desymmetrization of 1,3‐difluorides by silicon‐induced selective C?F bond scission is a key step. The combination of a cinchona alkaloid based chiral ammonium bifluoride catalyst and N,O‐bis(trimethylsilyl)acetoamide (BSA) as the silicon reagent enabled the efficient catalytic cycle of asymmetric Csp3?F bond cleavage under mild conditions with high enantioselectivities. The ortho effect of the aryl group at the prostereogenic center is remarkable. This concept was applied for the asymmetric synthesis of promising agrochemical compounds, 3,5‐diaryl‐5‐fluoromethyloxazolidin‐2‐ones bearing a quaternary carbon center. 相似文献
7.
Timothy B. Wright Ben W. H. Turnbull P. Andrew Evans 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(29):9991-9995
An enantioselective rhodium‐catalyzed allylic alkylation of β,γ‐unsaturated α‐amino nitriles is described. This protocol provides a novel approach for the construction of β‐stereogenic carbonyl derivatives via the catalytic asymmetric alkylation of a homoenolate equivalent. The particularly challenging nature of this transformation is highlighted by the fact that three modes of selectivity must be manipulated, namely regio‐ and enantioselectivity, in addition to geometrical control. The γ‐stereogenic cyanoenamine products can be readily hydrolyzed in situ to afford the β‐substituted carboxylic acids, which in turn provide expedient access to a number of related carbonyl derivatives. Additionally, control experiments indicate that the chiral rhodium‐allyl intermediate facilitates the selective formation of the E‐cyanoenamine products, which is critical since the Z‐isomer affords significantly lower enantiocontrol. 相似文献
8.
Kazuhiko Semba Masataka Shinomiya Prof. Dr. Tetsuaki Fujihara Prof. Dr. Jun Terao Prof. Dr. Yasushi Tsuji 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(22):7125-7132
The highly selective copper‐catalyzed hydroboration of allenes has been developed. Allylboranes and alkenylboranes were selectively prepared by the judicious choice of catalytic species (copper hydride and boryl copper). Furthermore, two types of alkenylboranes could be selectively synthesized by the choice of an appropriate ligand. Mechanistic studies confirmed that the protonation of a (Z)‐σ‐allyl copper species, which was isolated and structurally characterized by single‐crystal X‐ray diffraction, was a key step in these reactions. Besides allenes, this method is also applicable to the selective hydroboration of 1,3‐diene derivatives to afford allylboranes and homoallylboranes. 相似文献
9.
Starting from methyl 2,3‐O‐isopropylidene‐α‐D ‐mannofuranoside ( 5 ), methyl 6‐O‐benzyl‐2,3‐O‐isopropylidene‐α‐D ‐lyxo‐hexofuranosid‐5‐ulose ( 12 ) was prepared in three steps. The addition reaction of dimethyl phosphonate to 12 , followed by deoxygenation of 5‐OH group, provided the 5‐deoxy‐5‐dimethoxyphosphinyl‐α‐D ‐mannofuranoside derivative 15a and the β‐L ‐gulofuranoside isomer 15b . Reduction of 15a and 15b with sodium dihydrobis(2‐methoxyethoxy)aluminate, followed by the action of HCl and then H2O2, afforded the D ‐mannopyranose ( 17 ) and L ‐gulopyranose analog 21 , each having a phosphinyl group in the hemiacetal ring. These were converted to the corresponding 1,2,3,4,6‐penta‐O‐acetyl‐5‐methoxyphosphinyl derivatives 19 and 23 , respectively, structures and conformations (4C1 or 1C4, resp.) of which were established by 1H‐NMR spectroscopy. 相似文献
10.
Wenhui Zhang Bruce C. Noll Anthony S. Serianni 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(10):o578-o581
The β‐pyranose form, (III), of 3‐deoxy‐d ‐ribo‐hexose (3‐deoxy‐d ‐glucose), C6H12O5, crystallizes from water at 298 K in a slightly distorted 4C1 chair conformation. Structural analyses of (III), β‐d ‐glucopyranose, (IV), and 2‐deoxy‐β‐d ‐arabino‐hexopyranose (2‐deoxy‐β‐d ‐glucopyranose), (V), show significantly different C—O bond torsions involving the anomeric carbon, with the H—C—O—H torsion angle approaching an eclipsed conformation in (III) (−10.9°) compared with 32.8 and 32.5° in (IV) and (V), respectively. Ring carbon deoxygenation significantly affects the endo‐ and exocyclic C—C and C—O bond lengths throughout the pyranose ring, with longer bonds generally observed in the monodeoxygenated species (III) and (V) compared with (IV). These structural changes are attributed to differences in exocyclic C—O bond conformations and/or hydrogen‐bonding patterns superimposed on the direct (intrinsic) effect of monodeoxygenation. The exocyclic hydroxymethyl conformation in (III) (gt) differs from that observed in (IV) and (V) (gg). 相似文献
11.
Synthesis of Linear (Z)‐α,β‐Unsaturated Esters by Catalytic Cross‐Metathesis. The Influence of Acetonitrile
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Elsie C. Yu Brett M. Johnson Erik M. Townsend Prof. Richard R. Schrock Prof. Amir H. Hoveyda 《Angewandte Chemie (International ed. in English)》2016,55(42):13210-13214
Kinetically controlled catalytic cross‐metathesis reactions that generate (Z)‐α,β‐unsaturated esters selectively are disclosed. A key finding is that the presence of acetonitrile obviates the need for using excess amounts of a more valuable terminal alkene substrates. On the basis of X‐ray structure and spectroscopic investigations a rationale for the positive impact of acetonitrile is provided. Transformations leading to various E,Z‐dienoates are highly Z‐selective as well. Utility is highlighted by application to stereoselective synthesis of the C1–C12 fragment of biologically active natural product (?)‐laulimalide. 相似文献
12.
Ir(III)‐Catalyzed C7‐Position‐Selective Oxidative CH Alkenylation of Indolines with Alkenes in Air
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An efficient method for C7‐position‐selective alkenylation of N‐substituted indolines with alkenes is reported. Various 7‐alkenylindolines were obtained in moderate to excellent yields in air in the presence of catalytic amounts of [Cp*IrCl2]2, AgOTf, and Cu(OAc)2. The protocol relies on the use of a carbonyl or carbamoyl group on the nitrogen atom of indoline as a directing group and is potentially applicable to the synthesis of 7‐alkenylindoles and 7‐alkylindoles. 相似文献
13.
Hugo Quintela‐Varela Cooper S. Jamieson Qianzhen Shao K. N. Houk Dirk Trauner 《Angewandte Chemie (International ed. in English)》2020,59(13):5263-5267
The combination of electrocyclizations and cycloadditions accounts for the formation of a range of fascinating natural products. Cascades consisting of 8π electrocyclizations followed by a 6π electrocyclization and a cycloaddition are relatively common. We now report the synthesis of the tetramic acid PF‐1018 through an 8π electrocyclization, the product of which is immediately intercepted by a Diels–Alder cycloaddition. The success of this pericyclic cascade was critically dependent on the substitution pattern of the starting polyene and could be rationalized through DFT calculations. The completion of the synthesis required the instalment of a trisubstituted double bond by radical deoxygenation. An unexpected side product formed through 4‐exo‐trig radical cyclization could be recycled through an unprecedented triflation/fragmentation. 相似文献
14.
An expedient concise total synthesis of (+)‐7‐epigoniodiol, (?)‐8‐epigoniodiol, and (+)‐9‐deoxygoniopypyrone is accomplished. The key transformations include a catalytic hydroxylation and base‐mediated N‐(acetyl)oxazolidinone addition reactions, which could set the consecutive OH motif that is either syn,syn or syn,anti with high diastereoselectivity. Moreover, this approach envisioned to facilitate the synthesis of other representatives of the family with structural and stereochemical variation. 相似文献
15.
Dr. Peter K. Dornan Zachary K. Wickens Prof. Robert H. Grubbs 《Angewandte Chemie (International ed. in English)》2015,54(24):7134-7138
A stereoselective synthesis of anti‐1,2‐diols has been developed using a multitasking Ru catalyst in an assisted tandem catalysis protocol. A cyclometalated Ru complex catalyzes first a Z‐selective cross‐metathesis of two terminal olefins, followed by a stereospecific dihydroxylation. Both steps are catalyzed by Ru, as the Ru complex is converted to a dihydroxylation catalyst upon addition of NaIO4. A variety of olefins were transformed into valuable, highly functionalized, and stereodefined molecules. Mechanistic experiments were performed to probe the nature of the oxidation step and catalyst inhibition pathways. These experiments point the way to more broadly applicable tandem catalytic transformations. 相似文献
16.
Thomas Kull Dr. José Cabrera Dr. René Peters Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(30):9132-9139
The development of the first trans‐selective catalytic asymmetric [2+2] cyclocondensation of acyl halides with aliphatic aldehydes furnishing 3,4‐disubstituted β‐lactones is described. This work made use of a new strategy within the context of asymmetric dual activation catalysis: it combines the concepts of Lewis acid and organic aprotic ion pair catalysis in a single catalyst system. The methodology could also be applied to aromatic aldehydes and offers broad applicability (29 examples). The utility was further demonstrated by nucleophilic ring‐opening reactions that provide highly enantiomerically enriched anti‐aldol products. 相似文献
17.
《中国化学》2017,35(8):1231-1238
The double Michael reactions between benzofuran‐3‐one or 1‐indone and symmetric dienones in the presence of catalytic ionic liquids were successfully developed and spiro[benzofuran‐2,1’‐cyclohexane]‐3‐one or spiro[cyclohexane‐1,2’‐indene]‐1’,4(3’H )‐dione derivatives containing a spiro quaternary stereogenic center, which widely exist in biologically active products and building blocks in organic synthesis, were obtained in excellent yields (up to 99%). This catalytic system was also extended to the double Michael reaction of less reactive 1‐indone and the desired products were also obtained in 31%‐62% yields. The catalytic system was highly active and efficient for a broad of substrates under mild conditions. 相似文献
18.
A convenient synthis for 4‐substituted and 3,4‐disubstituted 1,7‐naphthyridine‐2(1H)‐thiones 7 has been developed. The method is based on the electrocyclic reaction of 4‐(1‐arylalk‐1‐enyl)‐3‐isothiocyanatopyridines 6 , generated in situ by the treatment of the respective isocyanides 5 with S8 in the presence of a catalytic amount of selenium. The isocyanides 5 can be easily prepared from commercially available pyridin‐3‐amine by conventional organic reactions. 相似文献
19.
Matthew V. Joannou Brandon S. Moyer Matthew J. Goldfogel Prof. Simon J. Meek 《Angewandte Chemie (International ed. in English)》2015,54(47):14141-14145
A catalytic protocol for the diastereoselective synthesis of anti‐1,2‐hydroxyboronates is described. The process provides access to secondary alkyl organoborons. The deborylative 1,2‐addition reactions of alkyl 1,1‐diborons proceed in the presence of a silver(I) salt with either KOtBu or nBuLi as an activator. The catalytic diastereoselective protocol can be extended to aryl, alkenyl, and alkyl aldehydes with up to 99:1 d.r. 相似文献
20.
《应用有机金属化学》2017,31(11)
The synthesis, characterization and catalytic activity of chloroaluminate ionic liquid‐modified silica‐coated magnetic nanoparticles ([SiPrPy]AlCl4@MNPs) are described. The prepared magnetic nanocatalyst was characterized using Fourier transform infrared spectroscopy, elemental analysis, vibrating sample magnetometry, scanning and transmission electron microscopies, X‐ray diffraction and inductively coupled plasma analysis. The results showed that the ionic liquid had been successfully immobilized onto the magnetic support, and the resulting nanoparticles exhibited high catalytic activity for the synthesis of a diverse range of dihydropyrano[3,2‐b ]chromenediones via a one‐pot, three‐component and solvent‐free reaction of aromatic aldehydes, 1,3‐diones and kojic acid. This catalytic system also showed excellent activity in the selective synthesis of mono‐ and bis‐dihydropyrano[3,2‐b ]chromenediones from dialdehydes. The procedure gave the products in excellent yields and in very short reaction times. Moreover, the catalyst could be reused eight times without loss of its catalytic activity. 相似文献