Heterocyclic analogues of cyclopentadienylidenecycloheptatriene derived from 1,3,4-oxadiazole and 1,2,4-triazole

Abstract

Heterocyclic systems having the same π-electron configuration as cyclopentadienylidenecycloheptatriene are of two types, covalent and dipolar. The stable covalent 2-fluoren-9-ylidene-3,5-dimethyl-Δ⁴-1,3,4-oxadiazoline (10) and 5-fluoren-9-ylidene-1,3,4-trimethyl-Δ²-1,2,4-triazoline (15) have been prepared starting with fluorene-9-carbohydrazide. The synthesis of the unstable dipolar anhydro-5-fluoren-9-yl-2,3-diphenyl-1,3,4-oxadiazolium hydroxide (20) and attempts to obtain its 5-diphenylmethyl analogue are described.