Regioselectivity in the 1,3-dipolar cycloaddition of nitrile oxides to 3,3-methylene-5,5-dimethyl-2-pyrrolidinone

Abstract

Nitrile oxides add regioselectively to the carbon-carbon double bond of 3,3-methylene-5,5-dimethyl-2-pyrrolidinone (1), giving exclusively spiro-isoxazolines: 3-aryl-6-oxo-8,8-dimethyl-1-oxa-2,7-diazaspiro[4.4]non-2-enes3 a–l. The regiochemistry of the 1,3-dipolar cycloaddition to 1 seems to be controlled by the steric effect of the methyl groups at the ring junction and by frontier orbital interactions.