Stereodirecting effects in the characterization of ylide intermediates in reactions of singlet methylene with an allylic ether and an allylic chloride

The stereodirecting effects of substrate substituents were examined in addition of (1):CH2 to the double bonds of 3-methoxycyclohexene (3a), 3-chlorocyclohexene (3b), and 3-methylcyclohexene (3c) in pentane solution at temperatures from 23 degrees C ro: -50 degrees C. A preference for addition syn to the directing substituent was observed in reactions of 3a and 3b and was attributed to a reversible interaction of carbene and substituent. In the reaction with 3a this interaction was not obviously ylide formation. (C) 1997 Elsevier Science Ltd.