Substituent effects in the generation and trapping of 1,2-dichloro-3,3-dialkylbut-2-en-1-ylidenes

The ring-opening of cyclopropenes (1) to carbenes (3) occurs more readily when X is an electron releasing group. The selectivity of carbenes (3, X = H, OMe) towards alkanes correlates well with that for tetrachloroprop-2-en-1-ylidene.