Synthetic approaches to bicyclic diazenium salts.

Bicyclic diazenium salts have been prepared from α-chloroazo species via a Lewis acid-mediated intramolecular cycloaddition. An alternative, more direct, route to these salts by the reaction of hydrazones with dimethylsulfonium ditriflate is also described. Terminal olefins provided mixtures of fused and bridged bicyclic diazenium salts. The ratio of the fused and bridged species was observed to depend on the electronics of the N-aryl substituent, which is explained by considering a concerted asynchronous cycloaddition mechanism.