Tetrahedron

Ethoxyacetylene and ethyl vinyl ether, dipolarophiles of opposite regiochemistry in diazomethane cycloadditions

R Sustmann, W Sicking, M Felderhoff

Index: Sustmann, Reiner; Sicking, Willi; Felderhoff, Michael Tetrahedron, 1990 , vol. 46, # 3 p. 783 - 792

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Citation Number: 26

Abstract

Diazomethane adds to ethoxyacetylene to give a 96: 4 mixture in favor of 4-ethoxypyrazole (3) which had been identified as the only product in a previous study. This result contrasts the behavior of ethyl vinyl ether which gives 3-ethoxy-1-pyrazoline (2). Transition structures for the four possible regioisomers are determined by MNDO-PM3 calculations. The regioselectivity is explained on the basis of the PM3 calculations and their perturbational ...