Unexpected formation of derivatives of cyclobutene and thiacyclobutane from the reaction between dilithiated benzylacetylene and isothiocyanates

Reaction of dilithiated benzylacetylene PhCH(Li)-C=C-Li with one equivalent of an isothiocyanate RN-C=S followed by successive addition of r-BuOH, a solution of t-BuOK in DMSO and methyl iodide gives exclusively a cyclobutene or a thietane derivative if R=t-Bu or Ph, respectively, and mixtures of the expected thiophene. the cyclobutene and thietane derivatives if R = Me, (C) 2001 Published by Elsevier Science Ltd.