1,2-DICHLORO-3,3-DIMETHYLCYCLOPROPENE AS A SOURCE OF 1,2-DICHLORO-3-METHYLBUT-2-ENYLIDENE AT AMBIENT TEMPERATURE

Article abstract of DOI:10.1016/S0040-4020(01)85133-4

Reaction of 2-bromo-1,1,2-trichloro-3,3-dimethylcyclopropane with one mol.equiv. of methyl lithium at -90 to 0 deg C leads to 1,2-dichloro-3,3-dimethylcyclopropene.This is stable for several hours at 20 deg C in chloroform or benzene solution but in the presence of an electron-rich or electron-poor alkene reacts in 15 m to 2 h under these conditions to give products apparently derived by reaction of these with 1,2-dichloro-3-methylbut-2-en-1-ylidene (4).The corresponding products are also obtained when 1,1,2-trichloro- or 1,1,2,2-tetrachloro-3,3-dimethylcyclopropanes are treated with methyl lithium in the presence of alkenes at 0 - 20 deg C.The cyclopropene (3) is stable in ether solution for more than 10 days at -30 deg C, but at ambient temperature reacts in 18 h to give the product of insertion of the carbene (4) into the C-H bonds adjacent to oxygen.