MECHANISTIC STUDY OF THE REACTIONS OF 1,1-DIHALO-2-METHYL-2-PHENYLPROPANES WITH LDA - EVIDENCE FOR RADICAL AND CARBENE PATHWAYS

An attempt was made to determine the mechanisms involved in the reacti ons of the model systems 1,1-dichloro-2-methyl-2-phenylpropane (1) and 1,1-diiodo-2-methyl-2-phenylpropane (2) with LDA. These systems were chosen as ones capable of providing evidence for the formation of radi cal as well as carbene products. The techniques employed in investigat ing the mechanistic features of these reactions involved studying the effect of the leaving group, the effect of radical and carbene trappin g agents on the product distribution, and isotopic tracer experiments using labeled solvent (THF-d(8)) and nucleophile (LDA-d(2)). The major product of the reaction of the geminal dichloride (1) is thought to b e derived from a chlorocarbene, whereas the geminal diiodide (2) appea rs to form products derived from both carbene and radical intermediate s. On the basis of the results of radical trapping experiments and tho se of deuterium-labeling experiments, evidence is presented to support the notion that products A, E, and H are derived from a radical precu rsor. In addition, products A and H are also believed to be formed fro m the vinylic halide D (or B) and the monoiodide E, respectively. Reas onable mechanisms for the formation of the other products formed in th ese reactions have been proposed on the basis of the available data.