REGIOSELECTIVITY, STEREOSELECTIVITY, AND ENANTIOSELECTIVITY IN THE ELECTROPHILIC REACTIONS OF 2-AMINO-4-PHENYL-3-BUTENENITRILES

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.