Quasi-Concerted Allylic Rearrangement in the Reaction of Allylic Chlorides with Methyltin Tris(methanethiolate)

Article abstract of DOI:10.1021/jo00189a023

trans-6-Chloro-4-decene (4), 3-chloro-1-heptene (7), and trans-1-chloro-2-heptene (9) are converted quantitatively into allylic methyl sulfides upon treatment with a molar equivalent of methyltin tris(methanethiolate) at 70 deg C in benzene-dichloromethane.Unlike the reactions of sodium thiolates with straight chain allylic chlorides, these nucleophilic displacements are accompanied by very significant amounts of allylic rearrangement, with the yields of rearranged sulfide being 78percent and 100percent for 4 and 7, respectively.In the case of 9, the yield of rearranged product drops from 33percent to 25percent when the extent of conversion increases from 40percent to 100percent.However, all of the product sulfides are stable under the reaction conditions, and the reactions seem to occur without concomitant dehydrochlorination or isomerization of the starting chlorides.Other salient features of these reactions are their autoaccelerating rates, a chloride reactivity order like that observed for S_N1 solvolysis, the production of internal double bonds that are exclusively trans, and the failure of methanethiol to react with 4 in a control experiment.An attractive reaction mechanism, not yet established conclusively, involves the discharge of unsymmetrical (allylic cation) MeSn(SMe)_nCl^-_4-n ion pairs (n = 1-3) via MeS ligand transfer.The implications of this investigation for the thermal stabilization of poly(vinyl chloride) are considered briefly, and the 13C NMR chemical shifts of several allylic chlorides and methyl sulfides are used to derive parameters that can be employed for shift predictions.