Origins of Regioselectivity in the Reactions of .alpha.-Lactams with Nucleophiles
摘要:
Regioselectivity in the reaction of alpha-lactams with nucleophiles results from two competing steps. Nucleophilic addition to the carbonyl group of the alpha-lactam, which yields rearranged, acyl-substituted products, is dependent on the nucleophilicity and the concentration of the nucleophile. Ring opening of the alpha-lactam to an ion pair intermediate, which gives nucleophile incorporation at C-2, is dependent on electronic effects of substituents at C-2. Groups which can stabilize positive charge at C-2 speed up ion pair formation, whereas electron-withdrawing groups slow the ring opening and give more carbonyl addition product. These factors are used to control the regioselectivity and produce a series of unsymmetric urea peptide mimetics in high yields and with complete regiochemical control.