Methyl exchange on silicon during the addition of methylmagnesium iodide to a cyanohydrin O-silyl ether

Reaction of [C-13]methylmagnesium iodide (99 atom% C-13) with cyanohydrin O -trimethylsilyl ether 1, followed by acidic hydrolysis, led to the formatio n of a methyl ketone derivative 2a that was only partially labelled (60 +/- 5 atom% C-13); this loss of labelling occurred through a methyl exchange r eaction on silicon as shown by the presence on intermediate 2b of [C-13]met hyl groups on silicon (30 atom% C-13).