Steric and Electronic Factors in 1,3-Dipolar Cycloadditions. The Stereochemical Course of the Addition of Dimethyl Aryl- and Alkyldiazomethylphosphonates to Norbornadiene

Abstract

The addition of 14 dimethyl aryl- and alkyldiazomethylphosphonates, RC(N 2 )P(O)(OCH 3 ) 2 , to norbornadiene has been studied and the stereochemistry of the resulting exo-Δ 1 -pyrazolines determined by n.m.r. The anti/syn ratio of the cycloadducts is discussed in terms of steric and electronic factors. For alkyldiazomethylphosphonates steric factors are the dominant ones, while with aryldiazomethylphos-phonates electronic factors seem to be of importance.