Theoretical Investigation on Asymmetric Diels?Alder Reactions of 2,4-Dienones Catalyzed by Trienamine Catalyst

초록

The mechanism and the origin of selectivity of asymmetric Diels-Alder reactions of 2,4-dienones have been investigated by B3LYP method with 6-31G* level. Calculations indicate that 9-amino-9- deoxyepiquinine reacts with dienone to form a key trienamine catalytic species, which could act as a diene in the DA reaction with an electron-deficient dienophile. The acidic additive (salicylic acid or trifluoroacetic acid) plays a key role to produce preferred conformation of trienamine by H atom transfer from δ-substituted methyl group to quinuclidine moiety in quinine. The protonated tertiary N atom of quinine activates dienophile substrate by hydrogen bonding. The transition state with the lowest energy barrier corresponds to the product with endo selectivity, which is in good agreement with experimental observations.