2.3- Dimethylenecyclohexane-l,4-diyl

It would appear that the 2,3-dimethylenecyclohexane-l,4-diyl biradical is involved in this reaction, and it was generated independently by flash photolysis of the appropriate azo compound and ketone and found to give 3,4-dimethylene-1,5-hexadiene and bicyclo[4.2.0]octa-l,5-diene in a 1 2 ratio in solution with log = 16.5 - 24500/23RT (Scheme 9.71). ° ... 

Dimethylenebicyclo[2.2.0]hexane gave a 1 2 mixture 3,4-dimethylene-1,5-hexadiene and bicyclo[4.2.0]octa-1,5-diene at 100°C in the gas phase. The reaction appears to proceed via the 2,3-dimethylenecyclohexane-l,4-diyl (Scheme 9.72). In solution, dimers were formed that gave rise to CIDNP emission signals when formed in an NMR probe indicating triplet precursors. 

CBD = cyclobutadiene COT = cyclooctatetraene DMCHD = 2,3-dimethylenecyclohexane-l,4-diyl DMCPD = 4,5-dimethylenecyclopentane-1,3-diyl MBQDM = /n-benzo-quinodimethane TM = trimethylene TMB = tetramethylene-benzene TME = tetramethyleneethane TMM = trimethylene-methane TST = transition state theory. 

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