Control of regiochemistry in nitrone cycloadditions. Regioselectivity of the reactions of trisubstituted nitrones with electron-deficient and conjugated dipolarophiles
作者:Marina Burdisso、Remo Gandolfi、Paolo Grünanger
DOI:10.1016/s0040-4020(01)89503-x
日期:1989.1
temperatures. Under these latter conditions the 5-substituted isoxazolidine was clearly prevalent owing to its being sterically less congested than the 4-substituted derivative. Evaluation of relative cycloaddition rates for 1a showed that the activating effect of formyl (rel. rate = 1.5) and acetyl groups (1.00) is about five times higher than that of cyano (0.18) and methoxycarbonyl groups (0.22) whilst