Synthesis of 3,4-Bis(benzylidene)cyclobutenes

Abstract

The syntheses of several derivatives of 3,4-bis(benzylidene)cyclobutene are reported. Previously unknown 1,2-dibromo-3,4-bis(benzylidene)cyclobutene was obtained through in situ generation of 1,6-diphenyl-3,4-dibromo-1,2,4,5-tetraene followed by electrocyclic ring closure. Ensuing reduction and metal-catalyzed cross-coupling provided additional derivatives. The effects of ring strain on the geometry and electronics of these derivatives were examined by X-ray crystallography and 1 H NMR spectroscopy, respectively.

The chemistry of bisallenes

“…It isomerizes to the 3,4-dibromobisallene derivative next, especially under the influence of CuBr. The bisallene can subsequently undergo a CuBr-induced cyclization to a 1,2-dibromo-3,4-bismethylenecyclobutene derivative (see Section 1.4.1), thus providing a convenient route to these preparatively interesting four-membered ring compounds [64]. …”

“…Compounds of this general type, in which the three-membered rings are replaced by five- and six-membered rings, 450 and 451 respectively, have been prepared though [42,58–64]. The four-membered analogue of 449 is also unknown.…”