A facile synthesis of 6-[(4-nitrophenyl)thio]-substituted 2-methylene-2,3-dihydro-1,4-oxazepines from N-propargylic beta-enaminones

A one-pot process for the synthesis of 6-[(4-nitrophenyl)thio]-substituted 2-methylene-2,3-dihydro-1,4-oxazepines is reported. When reacted with 4-nitrobenzenesulfenyl chloride, N-propargylic beta-enaminones afforded alpha-sulfenylated N-propargylic beta-enaminones, which, in the presence of zinc chloride, underwent electrophilic cyclization to yield 6-[(4-nitrophenyl)thio]-substituted 2-methylene-2,3-dihydro-1,4-oxazepines. Process was found to be general for various N-propargylic beta-enaminones along with large substrate scope and high functional group tolerance. This operationally easy method may provide quick access to a library of functionalized 1,4-oxazepines of pharmacological interest.