Uncatalyzed Cationic Olefin Cyclizations of N-Vinylic α-Chloro-α-thioacetamides. Formation of β- and γ-Lactams

Article abstract of DOI:10.1016/0040-4020(95)00056-E

N-Vinylic α-chloro-α-thioacetamides were found to cyclize without a catalyst in two different manners depending upon the nature of the substituents at the terminus of the N-vinylic bond.Thus, bis(phenylthio)-substituted enamides 8a-c cyclized in a 4-exo-trig manner to give 4-methylene-β-lactams 10a-c, whereas mono(phenylthio)-, monophenyl-, and dialkyl-substituted congeners 23a,b, 28, and 38 cyclized in a 5-endo-trig manner to give γ-lactams 26a,b, 30, and 39, respectively.The product 38 was transformed into an anticonvulsant agent ethosuximide (42).