Endo and regioselectivity in 1,3-dipolar cycloaddition of pyridazinium N-ylides with a non-symmetrical cyclic olefin

Abstract

The 1,3-dipolar cycloaddition between pyridazinium N-ylides 3 and 3-methyl-Nphenylmaleimide was studied. In the case of pyridazinium phenacylides 4a-c the reaction was endo and regioselective, while in the case of carbomethoxymethylide 4d the cycloaddition gave two endo isomers in a 2:1 ratio. The stereochemistry of the adducts 6a-c and 7a,b was determined by NMR spectroscopy and confirmed by X-ray analysis for a representative compound, namely 6b.