Stereochemistry of the 1,3-dipolar cycloaddition reaction between N-(phenanthridin-5-io)benzamidate and olefins

Abstract

N-(Phenanthridin-5-io)benzamidate reacts with activated olefins such as N-methylmaleimide, maleic anhydride, dimethyl maleate, dimethyl fumarate, methyl acrylate, methyl methacrylate, and methyl trans-crotonate to give 1 : 1 cycloadducts, whose stereochemistry has been deduced from n.m.r. spectroscopic data. The adducts from N-methylmaleimide, maleic anhydride, and dimethyl maleate have the all-cis(2H,3H,3aH)-stereochemistry. These results are rationalised in terms of secondary molecular orbital interactions. With acrylates such stereospecificity is lost, suggesting that this effect is of lesser importance.