Unexpected thorpe reaction of an α-alkoxynitrile

alpha-Alkoxynitrile 1 in the presence of tris(methylthio) methyllithium 2 at -78 degrees C gave the dimer 5 instead of the expected Ci-elongated product 3. The formation of compound 5 is explained in terms of anion formation and self-condensation, a variant of the Thorpe reaction. Scrutinizing the H-1 NMR spectra revealed that the enamine tautomer 5b is predominant over the imine 5a in the solvents investigated.