Steric Effects on the Regioselectivity in Two-Step Diels–Alder Reactions of 1,2,4,5-Tetrazines with 2-Cyclopropylidene-4,5-dihydro-1,3-dimethyl-imidazolidine
作者:Klaus-Peter Hartmann、Manfred Heuschmann
DOI:10.1016/s0040-4020(00)00346-x
日期:2000.6
The regioselectivity of the two-stepDiels–Alderreaction of unsymmetrically substituted tetrazines 4 with 2-cyclopropylidene-imidazolidine 6 is investigated. The first reversible step of the cycloaddition affording zwitterions 7 and 8 is controlled by steric effects, which are explained using a simple model. The overall regioselectivity, however, is determined in the second step of the cycloaddition