Regio-, stereo-, and enantioselectivity in the electrophilic reactions of 2-amino-4-phenyl-3-butenenitriles
摘要:
The allylic anion generated from 2-(N-methylanilino)-4-phenyl-3-butenenitrile (1) reacted with iodomethane and 3-bromo-1-chloropropane in THF/HMPA to give the gamma-substitution products exclusively, predominantly in the 2Z-configuration. Substitution of the N-methylanilino group with the methyl ether of L-(-)-ephedrine resulted in the generation of chiral aminonitrile 2. Lithiated 2 reacted sluggishly in THF with allyl bromide and benzyl chloride in the absence of HMPA to give the gamma-substitution products predominantly in the 2Z-configuration, with little diastereoselectivity. The aminonitrile 3 prepared from cinnamaldehyde, L-(-)-ephedrine, and KCN was lithiated with 2 equiv of LDA resulting in high facial selectivity (76-100% diastereomeric excess) in alkylations in the presence of HMPA and LiI. Lithiated 3 reacted with propionaldehyde, benzaldehyde, and p-bromobenzaldehyde at-78-degrees-C to give the gamma-addition products, predominantly in the 4R-configuration (64-78% de). The stereochemistry of the isomers of each product was determined by chemical correlation and spectral methods including analyses of the CD spectra and X-ray diffraction. A bicyclic transition state C wherein lithium is chelated by both amino and alkoxy groups is proposed to interpret the observed stereoselectivity.
Regio-, stereo-, and enantioselectivity in the electrophilic reactions of 2-amino-4-phenyl-3-butenenitriles
摘要:
The allylic anion generated from 2-(N-methylanilino)-4-phenyl-3-butenenitrile (1) reacted with iodomethane and 3-bromo-1-chloropropane in THF/HMPA to give the gamma-substitution products exclusively, predominantly in the 2Z-configuration. Substitution of the N-methylanilino group with the methyl ether of L-(-)-ephedrine resulted in the generation of chiral aminonitrile 2. Lithiated 2 reacted sluggishly in THF with allyl bromide and benzyl chloride in the absence of HMPA to give the gamma-substitution products predominantly in the 2Z-configuration, with little diastereoselectivity. The aminonitrile 3 prepared from cinnamaldehyde, L-(-)-ephedrine, and KCN was lithiated with 2 equiv of LDA resulting in high facial selectivity (76-100% diastereomeric excess) in alkylations in the presence of HMPA and LiI. Lithiated 3 reacted with propionaldehyde, benzaldehyde, and p-bromobenzaldehyde at-78-degrees-C to give the gamma-addition products, predominantly in the 4R-configuration (64-78% de). The stereochemistry of the isomers of each product was determined by chemical correlation and spectral methods including analyses of the CD spectra and X-ray diffraction. A bicyclic transition state C wherein lithium is chelated by both amino and alkoxy groups is proposed to interpret the observed stereoselectivity.
A serial of imidazolium chiral ionic liquids starting from commercially available (â)-menthol as a chiral pool have been synthesized and successfully used for catalyzing conjugate umpolung of α,β-unsaturated aldehydes to stereoselectively synthesize γ-butyrolactones. The catalytic activities of these ionic liquids are examined and compared. The reaction of trans-cinnamaldehyde and p-methoxycarbonyl benzaldehyde as a model has been investigated in detail, and the reaction conditions have been optimized. Under the selected conditions, the ionic liquid catalyst can catalyze the annulations of trans-cinnamaldehyde with different aromatic aldehydes to afford differently substituted γ-butyrolactones. The recyclability of the ionic liquid catalyst is investigated, and the results have indicated that the catalyst can be recycled six times without obvious activity decreasing.
An efficient and flexible synthesis of a new class of chiral bifunctional NHC catalyst has been reported. These new imidazolylidene NHCs, bearing a (thio)urea function as a hydrogenbonddonor promoted efficiently highly diastereoselective trans‐cyclopentannulation of enals and enones in moderate to good yields (up to 69 % yield) along with excellent enantioselectivity (up to 96 % ee). This methodology
An asymmetric homoenolate cross-annulation of enals and aldehydes with high enantioselectivity is realized by NHC-catalyzed chemoselective umpolung of enals. The reaction proceeds in a highly chemoselective manner, selectively generating the conjugated Breslow intermediates fromenals rather than aldehydes, enabling the homoenolate addition of enals to aldehydes in preference to competing acyl anion-mediated
Cu-Catalyzed Asymmetric Arylation of Enone Diesters with Arylboronic Acids
作者:Noritaka Kunitomo、Taichi Kano
DOI:10.1021/acs.joc.4c01045
日期:2024.8.2
The Cu-catalyzed asymmetric conjugate addition of arylboronic acids to enone diesters is reported. This operationallysimple and scalable reaction proceeded under mild conditions. The practical utility of this approach was demonstrated by the synthesis of structurally important γ-lactones and a cyclopentene that bear an aryl group. Mechanistic studies revealed that two different copper catalytic species