Addition of Diphenylmethylene to 1,2-Dichloroethylenes. New Chemical Evidence for a Carbene Singlet-Triplet Equilibrium

Article abstract of DOI:10.1021/ja00539a023

Addition of diphenylmethylene to cis- and trans-1,2-dichloroethylene gives the corresponding 1,2-dichloro-3,3-diphenylcyclopropane with greater than 90percent stereospecificity.A product of addition with rearrangement, 3,3-dichloro-1,1-diphenyl-1-propene, is also obtained, and this is the major product from trans olefin.The cyclopropane product is believed to arise principally from concerted addition by the singlet carbene, while the rearrangement product is assigned to the triplet carbene.This result confirms earlier indications that dihaloethylenes can provide a clear chemical distinction between singlet and triplet carbenes by yielding quite different products from the two spin states.Neither competition from another olefin nor moderation by hexafluorobenzene alters the product ratio from addition of diphenylmethylene to dichloroethylenes, and this is new chemical evidence for the establishment of a singlet-triplet equilibrium for diphenylmethylene under the conditions employed for olefin addition reactions.