The rearrangements of 1,4-disubstituted 4-chloromethyl-3,5-dicyano-2,6-dimethyl-1,4-dihydropyridines to 1,4-disubstituted 3,6-dicyano-2,7-dimethyl-1H-azepines

Abstract

An investigation of the rearrangements caused by the action of sodium t-butoxide on certain N-substituted 4-chloromethyl-4-methyl- and 4,4-bischloromethyl-3,5-dicyano-2,6-dimethyl-1,4-dihydropyridines (VII) to N-substituted 4-methyl- or 4-chloromethyl-3,6-dicyano-2,7-dimethyl-1H-azepines (VIII) has revealed the existence of two types of intermediate. The first type has been identified as substituted 2-methylene-3-azabicyclo[4,1,0]hept-4-enes [e.g.(X)] and the second type as substituted 2-methylene-2,5-dihydro-1H-azepines [e.g.(XII)]. These intermediates are rearranged by acids to derivatives of 4-methylene-4,5-dihydro-1H-azepine [e.g.(XIII)] which may undergo a slow rearrangement to the 1H-azepines under the influence of acid at room temperature. Kinetic measurements have eliminated mechanisms based on a simple ionisation of the 4-chloromethyl-1,4-dihydropyridines or on carbene intermediates. Alternative mechanisms are suggested.