Abstract
AbstractThe 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)
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