Chiral biscinchona alkaloid promoted asymmetric allylic alkylation of 3-substituted benzofuran-2(3H)-ones with Morita-Baylis-Hillman carbonates

A highly diastereo- and enantioselective asymmetric allylic alkylation reaction with respect to prochiral 3-substituted benzofuran-2(3H)-ones and MBH carbonate by a chiral biscinchona alkaloid catalyst was investigated. The corresponding adducts, containing a quaternary center at the C3-position of the benzofuran-2(3H)-one as well as a vicinal tertiary center, were generally obtained in high yields (up to 97%) with very good diastereo- (up to 98:2 dr) and enantioselectivities (up to 95% ee).     

Asymmetric Michael addition reactions of 3-substituted benzofuran-2(3H)-ones to nitroolefins catalyzed by a bifunctional tertiary-amine thiourea

The current work reports an organocatalytic strategy for the asymmetric catalysis of chiral benzofuran-2(3H)-ones bearing 3-position all-carbon quaternary stereocenters. Accordingly, highly enantioselective Michael addition reactions of 3-substituted benzofuran-2(3H)-ones to nitroolefins have been developed by utilizing a bifunctional tertiary-amine thiourea catalyst. The reactions accommodate a number of nitroolefins and 3-substituted benzofuran-2(3H)-ones to give the desired chiral benzofuran-2(3H)-one products with moderate to excellent yields (up to 98%) and moderate to very good selectivities (up to 19?:?1 dr and up to 91% ee). Theoretical calculations using the DFT method on the origin of the stereoselectivity were conducted. The effect of the nitroolefin substituent position on the stereoselectivity of the Michael addition reaction was also theoretically rationalized.     

苯并呋喃-2,3-二酮和丙酮的不对称Aldol反应

以脯氨酸作为催化剂催化苯并呋喃-2,3-二酮与丙酮的不对称Aldol反应, 高选择性地合成了一系列3位含有手性季碳中心的苯并呋喃酮类化合物.     

Elaboration of phosphoramidite ligands enabling palladium-catalyzed diastereo- and enantioselective all carbon [4+3] cycloaddition

A palladium-catalyzed diastereo-and enantioselective all carbon [4+3] cycloaddition of trimethylenemethane was developed by employing the elaborate tetrahydroquinoline-derived phosphoramidite ligand. The exclusive regioselectivity was realized by using the aromatization-driven diene indole-2,3-quinodimethanes, affording biologically important cyclohepta[b]indoles with excellent diastereo-, and enantioselectivities(up to 20:1 dr, 99% ee). Furthermore, the more challenging pyrrolidone-3,4-dienes, in the absence of aromatization force, were also compatible inthereaction, providing novel cyclohepta[c]pyrrol-1(2H)-ones with excellent regio-, diastereo-, and enantioselectivities(up to 20:1 rr, 20:1 dr, 99% ee).     

Chiral Lewis base-assisted Brønsted acid (LBBA)-catalyzed enantioselective cyclization of 2-geranylphenols

Chiral Lewis base-assisted Br?nsted acids (Chiral LBBAs) have been designed as new organocatalysts for biomimetic enantioselective cyclization. A salt of a chiral phosphonous acid diester with FSO(3)H catalyzes the enantioselective cyclization of 2-geranylphenols to give the desired trans-fused cyclized products with high diastereo- and enantioselectivities (up to 98:2 dr and 93% ee).     

A novel reaction of the ‘Huisgen zwitterion’ with benzofuran-2,3-diones: an efficient strategy for the synthesis of spirocyclic benzofuran-2-one derivatives

The nitrogen-based nucleophile generated from azodicarboxylate and triphenylphosphine displayed good reactivity toward benzofuran-2,3-diones to generate a variety of spirocyclic benzofuran-2-one derivatives. The reactions accommodate a number of benzofuran-2,3-diones and different dialkylazodicarboxylates to give the enriched functionalized 3-spirooxadiazole benzofuran-2-ones with moderate to good yields (up to 93%).     

Chirality transfer from guanidinium ylides to 3-alkenyl (or 3-alkynyl) aziridine-2-carboxylates and application to the syntheses of (2R,3S)-3-hydroxyleucinate and D-erythro-sphingosine

[Reaction: see text]. Reaction of chiral guanidinium ylides with alpha,beta-unsaturated aldehydes gives 3-(alpha,beta-unsaturated) aziridine-2-carboxylates in high diastereo- and enantioselectivities (up to 93% diastereomeric excess and 98% enantiomeric excess). 3-(1-methylvinyl)- and 3-[(E)-pentadec-1-enyl]aziridine-2-carboxylates were successfully employed to prepare (2R,3S)-3-hydroxyleucinate and d-erythro-sphingosine, respectively.     

A new insight into palladium-catalyzed reaction of 2-alkynylphenol with carbon monoxide

A novel and efficient pathway for the generation of 3-(benzofuran-3-ylmethylene)benzofuran-2(3H)-ones via a palladium-catalyzed carbonylative reaction of 2-alkynylphenol with carbon monoxide is described. The reaction proceeds through a double insertion of triple bonds during the reaction process. The products are obtained in good yields with high selectivity. A one-pot synthesis starting from 2-iodophenol and alkyne is presented as well.     

Rhodium-catalyzed Michael addition of arylboronic acids to 3-alkylenyloxindoles: asymmetric synthesis of functionalized oxindoles

The rhodium-catalyzed diastereo- and enantioselective Michael addition of arylboronic acids to 3-alkylenyloxindoles has been developed with (R)-binap as a ligand. A wide variety of the desired functionalized oxindoles are smoothly obtained in high yields (up to 99%) with high enantioselectivities (up to 92% ee) and good diastereoselectivities (up to 82:18).     

Diastereo- and enantioselective [3 + 2] cycloaddition reaction of Morita-Baylis-Hillman carbonates of isatins with N-phenylmaleimide catalyzed by Me-DuPhos

A Me-DuPhos-catalyzed efficient asymmetric [3 + 2] cycloaddition reaction between Morita-Baylis-Hillman carbonates of isatins and N-phenylmaleimide has been developed. This reaction constructs three chiral centers in one step to afford spirocyclopentaneoxindoles in good yields (up to 84%) with excellent diastereo- and enantioselectivies (up to 99% ee).     

Chiral phosphine-catalyzed asymmetric allylic alkylation of 3-substituted benzofuran-2(3H)-ones or oxindoles with Morita-Baylis-Hillman carbonates

An efficient chiral phosphine-catalyzed asymmetric substitution reaction of MBH carbonates with 3-substituted benzofuran-2(3H)-ones or 3-substituted oxindoles has been described in this context, giving the corresponding allylic alkylation products bearing adjacent quaternary and tertiary stereogenic centers in high yields, moderate diastereoselectivities and high enantioselectivities under mild conditions.     

Flexible Synthesis of Benzofuranones from ortho-Alkynyl Phenols or Benzofurans

Benzofuranones are attractive synthetic targets in medicinal and natural products. The cycloisomerization of o-alkynyl phenol to benzofuran-3(2H)-one is reported here using gold(I) and Selectfluor. This benzofuranone can also be obtained from benzofuran without a gold catalyst. This study presents two appealing synthetic methods for benzofuran-3(2H)-ones that use readily available starting materials, have high chemoselectivity and operate under very mild conditions.     

Synthesis of 3-aryl-2-arylamidobenzofurans based on the Curtius rearrangement

The synthesis of novel 3-aryl-2-arylamidobenzofurans has been accomplished via a Curtius rearrangement strategy in four steps from benzofuran-2-carboxylic acids. The requisite Suzuki-Miyaura cross-coupling, with benzyl 3-bromobenzofuran-2-ylcarbamate or 2-arylamido-3-bromobenzofurans, revealed an unusual reductive debromination process due to the presence of the free NH group. This dehalogenation can be suppressed by N-alkylation. DMAP is an efficient reagent for the one-pot conversion of benzyl benzofuran-2-ylcarbamates into the corresponding benzofuran-2-arylamides through aroylation, thus acting both as an acyl transfer reagent and a deprotecting agent of the Cbz group. A mechanism is postulated.     

Novel fungi-catalyzed reduction of α-alkyl-β-keto esters

A screening of 15 fungi and yeast strains was carried out in fermentation processes to perform the diastereo- and enantioselective reduction of ethyl 2-methyl-3-oxobutanoate, to the corresponding (R¹,S¹)-3-hydroxy-2-methyl esters. Overall, biotransformations led to excellent conversions, as well as good to excellent diastereo- and enantioselectivities. A strain of Aureobasidium pullulans (CCM H1) was found to be the most efficient biocatalyst in terms of conversion (100%), syn:anti ratio (3:97), and enantiomeric excess (94% anti-(2S,3S) isomer). This biotransformation was successfully carried out on a preparative level as well. Other microorganisms, such as Fusarium graminearum (CCM HH 224), Aspergillus terreus (BFQU 121), Geotrichum candidum (CCM H38), Trichoderma koningii (ATCC 76666), and Aspergillus niger (CCM H21) also showed excellent diastereo- and enantioselectivities, combined with high conversions (>95% conversion, ?95% ee, and excellent syn:anti ratios). Many of the strains used in this work had scarcely been described as oxido-reducing agents, or had never been used with the substrates reported herein.     

Enantioselective synthesis of imidazolines with quaternary stereocenters by organocatalytic reaction of N-(heteroarenesulfonyl)imines with isocyanoacetates

An organocatalytic enantioselective Mannich-type reaction of isocyanoacetate with N-sulfonylimines catalyzed by chiral thioureas derived from quinine yielded 2-imidazolines with high diastereo- and enantioselectivities (up to >99:1 dr. and 96% ee). This reaction provided a convenient route to access various imidazolines and related α,β-diamino acids having a quaternary carbon center in high enantiomeric purities.     

SbCl3-catalyzed solvent-free Friedel–Crafts reaction of phenols with mandelic acids to 3-aryl benzofuran-2(3H)-ones: Synthesis of spirocyclic 2,3-dihydrobenzofuran-2-ones

A facile, SbCl₃-catalyzed, one-pot, tandem Friedel–Crafts/lactonization reaction of phenols and mandelic acids has been developed under solvent-free conditions to afford 3-aryl benzofuran-2(3H)-ones in good to high yields (52–90%). Additionally, the utility of 3-aryl benzofuran-2(3H)-ones is demonstrated by using them as precursors in the synthesis of a new class of spirocyclic benzofuran-2-ones using classical synthetic methodologies.     

Highly enantioselective 1,3-dipolar cycloaddition of imino esters with benzofuranone derivatives catalyzed by thiourea−quaternary ammonium salt

Highly enantioselective 1, 3-dipolar cycloaddition of 2-arylidene-benzofuran- 3(2H)-ones with imino esters catalyzed by thiourea?quaternary ammonium salts has been developed. This reaction provides efficient construction of a range of chiral spiro[benzofuran-2,3′-pyrrolidine] in high yields (up to 99%) and with good enantioselectivities (up to 99% ee) under mild conditions.     

Asymmetric Friedel-Crafts alkylation of indoles with 3-nitro-2H-chromenes catalyzed by diphenylamine-linked bis(oxazoline) and bis(thiazoline) Zn(II) complexes

An efficient diastereo- and enantioselective Friedel-Crafts alkylation of indoles with 3-nitro-2H-chromenes catalyzed by diphenylamine-linked bis(oxazoline) and bis(thiazoline) Zn(II) complexes has been developed. This asymmetric Friedel-Crafts alkylation led to medicinally privileged indolyl(nitro)chromans in good yields with high enantioselectivities (up to 95% ee) and diastereoselectivities under mild reaction conditions.     

5-(4-叔丁氧基羰基哌嗪基)苯并呋喃-2-甲酸乙酯的合成

5-溴苯并呋喃-2-甲酸乙酯与4-叔丁氧基羰基哌嗪进行Buchwald-Hartwig偶联反应,若催化剂是Pd(OAc)2/BINAP,碱是Cs2CO3,则产物主要是5-(4-叔丁氧基羰基哌嗪基)苯并呋喃-2-甲酸乙酯,转化率达70%;若催化剂是Pd(dba)2/P(t-Bu)3,碱是叔丁醇钾,则产物中几乎没有5-(4-叔丁氧基羰基哌嗪基)苯并呋喃-2-甲酸乙酯.文中讨论了影响这个Buchwald-Hartwig偶联反应的因素.     

Catalytic Asymmetric Syntheses of Alkylidenecyclopropanes from Allenoates with Donor-Acceptor and Diacceptor Diazo Reagents

The first diastereo- and enantioselective cyclopropanation reactions of electron-deficient allenes with donor-acceptor and diacceptor diazo reagents are described. The desired enantioenriched alkylidenecyclopropanes (ACPs) were obtained in high yields with high diastereo- and enantioselectivities in the presence of Rh₂((S)-TCPTAD)₄ or Rh₂((R)-BTPCP)₄ catalysts (up to 95 % yield, >95 : 5 d.r. and 99 : 1 e.r.). This methodology gave a direct access to ACPs bearing multiple electron-deficient substituents and allows to further expand the availability of ACPs chemistry. Interestingly, during the examination of the scope of this reaction, the asymmetric intramolecular C−H insertion reaction into tert-butyl group was observed as a side reaction with up to 94 : 6 e.r.