Synthesis and characterization of 2H-, 3H- and 4H-azepine: the first observation of the thermal distribution equilibrium of azepines

Abstract

Demethoxycarbonylation of methyl 2,5,-di-tert-butyl-1H-azepine-1-carboxylate using 1,8-diazabicyclo[5.4.0]undec-7-ene gives exclusively two isomers of 3H-azepine derivatives, while methyl 3,6-di-tert-butyl-1H-azepine-1-carboxylate gives a mixture of 2H-, 3H- and 4H-azepine derivatives under the same conditions because of a 1,5-hydrogen shift in the resulting triene system.