C-H insertion reactions of nucleophilic carbenes

Syntheses and characterizations are described for C-H insertion products de rived from 1,3-dimesityldihydroimidazol-2-ylidene (1) with acetylene. aceto nitrile, methyl phenyl sulfone, and chloroform. In the reaction with acetyl ene, both acetylenic H-atoms are reactive so that 1 : 1 and 2 :1 adducts ca n be obtained. The acetylene and methyl-phenyl-sulfone adducts are structur ally characterized by means of single-crystal X-ray structure determination s. The reactions of 1,3,4,5-tetramethylimidazolidin-2-ylidene (8) with chlo roform or chlorodifluoromethane are shown to yield 2-(dihaloalkyl)imidazoli um salts that arise from a failure of the intermediate 2-protioimidazolium salt to capture the initially formed halocarbanion.