Cascade Vinyl Radical Ipso-Cyclization Reactions and the Formation of α,β-Unsaturated-β-aryl-γ-lactams from N-Propargyl Benzamides

Various N-(2-bromo-allyl) benzamides were used as the starting materials to study vinyl radical cyclization reactions. The vinyl radicals underwent ipso-cyclization, fragmentation, and cyclization reactions to produce beta-aryl-gamma-lactams with the carbonyl group remaining intact. To further study this cascade radical reaction, vinyl radicals were generated by the addition of a tributyltin radical to alkyne moieties, followed by radical ipso-cyclization, fragmentation, cyclization, and beta-scission reactions with the production of a series of alpha,beta-unsaturated-beta-aryl-gamma-lactam derivatives. This new type of radical reaction was examined from the substituent effects on both the amino groups and the aryl groups. A bulky tert-butyl substituent on the amino group enhanced the formation of a Z-conformation of the benzamides and facilitated vinyl radical ipso-cyclization reactions. A synthetic method for preparing alpha,beta-unsaturated-beta-aryl-gamma-lactams from N-propargyl benzamides was developed.

Automated summary

Various N-(2-bromo-allyl) benzamides were used as starting materials for studying vinyl radical cyclization reactions, which produced beta-aryl-gamma-lactams without affecting the carbonyl group. The cascade radical reaction led to the synthesis of alpha,beta-unsaturated-beta-aryl-gamma-lactam derivatives, with the effects of substituents on the amino and aryl groups examined.