Unusual Rearrangements in the C₁₂H₁₂‐Manifold 1,5,9‐Cyclododecatriyne, 1,2:3,4:5,6‐Tricyclobutabenzene, Hexaradialene

Abstract

1,5,9‐Cyclododecatriyne has been synthesized by a bromination‐dehydrobromination sequence starting from all‐cis‐1,5,9‐cyclododecatriene. Its physical properties point to substantial interaction of the acetylenic groups through space and through bond although this effect does not result in significant homoaromatic stabilization. Attempts to convert the triyne to isolable 1,2:3,4:S,6‐tricyclobutabenzene failed, but condensed phase thermolysis in the presence of dimethylmaleate led to the isolation of a formal triadduct. Flash pyrolysis resulted in the formation of hexaradialene. The latter is an extremely air sensitive, polymerizable molecule, devoid of detectable aromatic stabilization, in accord with theoretical treatments. Thermochemical estimates are presented which indicate the exothermicity of the 1,5,9‐cyclododecatriyne → hexaradialene interconversion. The most likely intermediate in this transformation is 1,2:3,4:5,6‐tricyclobutabenzene, also in accord with group equivalent calculations, although other pathways cannot be.ruled out rigorously.

(1E,5E)-2,5-Dibromocyclododeca-1,5-dien-9-yne

“…Dibromocyclododecatriene has been prepared as intermediate for the selective synthesis of (Z,Z,Z)-cyclododecatriene (Trauer & Haufe, 1988) and cyclotridecatrienes (Trauer & Haufe, 1990). The former is a valuable intermediate for the preparation of cyclododecatriyne (Barkovich & Vollhardt, 1976) and hexaradialene (Barkovich et al 1980). Currently, strained alkynes are central coupling partners in click chemistry.…”