A MECHANISTIC STUDY OF THE REACTIONS OF GEMINAL DIHALIDES WITH LDA - EVIDENCE FOR A SINGLE-ELECTRON TRANSFER PATHWAY IN THE REACTION OF GEMINAL DIIODIDES

While the reaction of the geminal dichloride, 6,6-dichloro-5,5-dimethy l-1-hexene (8a) with LDA afforded only one product, wh:ich was derived from a chlorocarbene intermediate, the reaction of the corresponding geminal diiodide 8b resulted in the formation of a number of products that were accounted for by a single electron transfer (SET) initiated reaction. This difference in the reactivity patterns of the two substr ates shows that the reduction potential of 8b is more favorable than t hat of 8a and that LDA can function as a one-electron donor. Additiona lly, 8a was more reactive toward LDA than the already studied monochlo ro substrate (1a) with the same carbon skeleton. This enhanced reactiv ity is attributed to the increased acidity of the hydrogen atom attach ed to the carbon bearing the two chlorine atoms in 8a. The observation that 8b reacted with LDA at a faster rate, not only relative to 8a bu t also to the corresponding monoiodo compound 1c, indicates that the r eduction potential of 8b is more favorable than that of 1c for SET red uction by LDA. Based on the nature of the products formed in the react ions of 8a and 8b with LDA, evidence is presented that supports the no tion that, in addition to funtioning as a strong base, LDA can also fu nction as a one-electron donor toward the geminal diiodide 8b.