3,3-Dimethyl-l-(p-tolylsulfonyl)-2-(trimethylsilyl)cyclopropene was prepared by the 1,3-dipolar cycloaddition of 2-diazopropane with p-tolyl2-(trimethylsilyl)ethyyl sulfone followed by photoextrusion of nitrogen from the resulting 3H-pyrazole. Treatment of this material with sodium methoxide produced trans-l-methoxy-2-@tolylsulfonyl)-3,3-dimethylcyclopropane. No detectable quantities of the cis isomer were present in the crude reaction mixture. The cyclopropyl carbanion derived from deprotonation of the (methoxysulfony1)-substituted cyclopropane reacts smoothly with a variety of electrophiles to give a single stereoisomer. The observed stereoselectivity can be rationalized in terms of intramolecular chelation of the cyclopropyl lithiate w i t h the neighboring methoxy group. The presence of an electronegative P-sulfonyl group also facilitates cyclopropyl carbanion interconversion. In this case the observed stereoselectivity is probably related to an anomeric effect. The favored cyclopropyl carbanion corresponds to the stereoisomer that permits interaction of the carbanion lone pair with the vacant u* orbital on the adjacent carbon containing the electronegative atom.
A new nitrone-based synthesis of the Nuphar indolizidine 5-(3-furyl)-8-methyloctahydroindolizine was accomplished by a regiospecific cycloaddition of a nitrone with a 1,4-disubstituted butadiene.
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