Organylthio(silyl)carbenes

The title carbenes 5 can be generated either from diazo compounds 9 by copper‐catalyzed catalysis or from chloro(organylthio)methylsilanes 12 by base‐induced α‐elimination. This is confirmed by [2+1] cycloadditions with alkenes to give the cyclopropanes 4a – d and 14 . Product 4a is identical with the product obtained from carbanion 1c , phenyloxirane, and styrene, for which a carbene intermediate 5a had been invoked. On heating in the presence of copper triflate, cyclopropane 4a undergoes ring enlargement to the thiochroman 11 . With ( Z )‐ or ( E )‐alkenes 20 , carbene 5a gives stereospecific cyclopropane formation, although maleate turns out not to be a suitable indicator for a stereospecific cycloaddition. The suggested singlet character of 5 is confirmed by DFT calculations (B3LYP/cc‐pVTZ). The structures of cyclopropanes 4a and 23 , as well as those of thiochroman 11 and carbene dimer 15 , were confirmed by single‐crystal X‐ray investigations.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)