Synthesis and reactivity of dibenzoselenacycloheptynes.

Dibenzoselenacycloheptynes were prepared in three steps from commercially available reagents and trapped in situ with benzyl azide to form the corresponding triazoles. Surprisingly, the dibenzoselenacycloheptynes also abstracted hydrogen atoms from solvents such as THF or toluene, forming dibenzoselenacycloheptene products. These alkenyl compounds arise from a hydrogen transfer reaction from solvent to the unisolable intermediate, and we postulate that the reaction proceeds via a radical mechanism originating from the strained alkynyl bond that has unusually high radical character.