ELECTRON-TRANSFER IN THE REACTIONS OF GEMINAL DIHALIDES WITH PH(2)P(-) - EVIDENCE FOR THE FORMATION OF A CARBENE INTERMEDIATE FROM A RADICAL PRECURSOR

The reactions of two sterically hindered geminal dihalides, 6,6-dichlo ro-5,5-dimethyl-1-hexene (5a) and 6,6-diiodo-5,5-dimethyl-1-hexene (5b ), with Ph(2)P(-) have been found to involve a single electron transfe r (SET) pathway. Since the corresponding monochloride reacts with Ph(2 )P(-) by a S(N)2 pathway, it is clear that adding a second chlorine at om on a carbon atom produces a more favorable reduction potential resu lting in a change in mechanism from S(N)2 to SET. Evidence is also pre sented that shows that the geminal dihalides produce carbene-derived p roducts and that the carbene was derived from a haloalkyl radical prec ursor.