Investigations Concerning an Unexpected Reaction Between the Dimsyl Anion (= (Methylsulfinyl)methanide) and a γ,δ-Epoxy-ketone.

The reaction of 2,2-dimethyl-5-(1,2-epoxypropyl)cyclohexanone (7) with t-BuOK in DMSO furnished a small amount of 5-(1-hydroxyprop-2-enyl)-2,2-dimethylcyclohexanone (12) and the 4 unexpected products 13–16 which contain one to three additional C-atoms (Scheme 2). The relative configuration of the major product 1-(4′,4′-dimethyl-2′,3′-dimethylidenecyclohexyl)propane-1,2-diol (15) was shown to be 1RS, 2RS,1′SR via NOE measurements performed on a derivative thereof. A crossover experiment in DMSO/[13C2]DMSO 1:1 as solvent showed that the two additional C-atoms of this product originate from a single molecule of DMSO (Scheme 5). A tentative mechanistic scheme, consistent with all experimental observations, is proposed which involves a [2,3]-sigmatropic rearrangement of an (allylsulfinyl)methanide to a sulfenic acid as one of the key steps (V 24, Scheme 8). We corroborated part of this hypothetic scheme by taking recourse to a model compound (7-(methylsulfinyl)-p-mentha-1,8-diene (32/33), readily prepared in two steps from perilla alcohol (30)), which reacted as predicted by the proposed mechanism (Schemes 9 and 10).