Reactions between lithiated 1,3-dithiane oxides and trialkylboranes

Abstract

Various 2-substituted-1,3-dithiane oxides (1-oxide and 1,3-dioxide) have been metalated and reacted for the first time with a trialkylborane (trioctylborane). The 2-chloro-1,3-dioxide results in migration of an octyl group from boron to carbon with the displacement of chloride and gives nonanoic acid after oxidation, but there is no evidence for a second migration involving displacement of a sulfenate group. The reaction involving lithiation of the 2-methoxy-1-oxide results in two migrations, with the displacement of both the methoxy group and the thiolate unit of the dithiane ring, giving dioctyl ketone after oxidation, but the yield is low, primarily because thiophilic addition of the lithiating agent predominates over lithiation. Again, there is no evidence for the displacement of the sulfenate unit. However, the intermediate prior to oxidation can be treated with trifluoroacetic anhydride to induce a Pummerer rearrangement, and the presumed trifluoroacetoxyalkylthiolate group then acts as a novel leaving group and is displaced, resulting in trioctylmethanol on oxidation, but the yield is again very low.