Synthesis of Bicyclic O- and N-Bridged Piperazines

Significance

The preparation of four structurally interesting bicyclic piperazines 1-4 is described. Starting from N,N-dibromobenzenesulfonamide and ethyl acrylate, the double addition product is obtained by a light-induced reaction. Interestingly, but unfortunately, only the minor meso isomer (25%) undergoes double diplacement reaction with benzylamine to give the desired piperazine, whereas the racemic isomer (60%) undergoes decomposition. After functional group interconversion, treatment with another equivalent of ben­zylamine leads to the bicyclic piperazine core structure 1. Surprisingly, with an excess of ben­zylamine and higher reaction temperature, a significant amount of isomer 3 is found.