Methyleneketenes and methylenecarbenes. XI. Rearrangements of cycloalkylidenecarbenes

Abstract

The products of flash vacuum pyrolysis of the cycloalkylidene derivatives (3) of Meldrum's acid at 480-640° are rationalized in terms of formation of the cycloalkylidenecarbenes (1; ring size n = 4-8)and their rearrangement to cycloalkynes, to bicyclic cyclopropenes (e.g. (7)), or to further products derived from these. Pyrolysis of the 3,3-dimethylcyclobutylidene derivative (3h) gave 3,5-dimethylphenol, probably formed by cyclization of the (Z)-hexatrienone (22).    

The tetrahydrofuran-3-ylidene derivative (3i) gave butatriene and formaldehyde as major products of pyrolysis; these may be formed by retro-Diels-Alder fission of the heterocycloalkyne (27).