Carbene chemistry. Part II. Migration in fluoroalkylcarbenes

Photolysis of 4-diazo-1,1,1,2,2,3,3-heptafluoropentane gives heptafluoropropyl(methyl)carbene, in which migration of hydrogen takes place to give 3,3,4,4,5,5,5-heptafluoropent-1-ene in high yield. Migration of fluorine or of the pentafluoroethyl group is not observed. The photolysis of 3-diazo-1,1,2,2-tetrafluoropropane gives the corresponding carbene in which migration of the difluoromethyl group is the major reaction; other minor products are believed to arise from a cyclopropane in an excited state, formed by insertion into the γ-CH bond.The exploration of routes to 2-diazo-1,1-difluoroethane and 2-diazo-1-fluoropropane, and the n.m.r. spectra of a number of compounds containing the CHF2·CF2· group are also reported.