XY–ZH systems as potential 1,3-dipoles. Part 7. Stereochemistry of the cycloaddition of imines of α-amino acid esters to fumarate and maleate esters

Abstract
Aryl imines of α-amino acid esters undergo 1,3-dipolar cycloadditions with maleate and fumarate esters in quantitative yield when heated in boiling toluene to give mixtures of mainly two pyrrolidines. The major isomer in each case arises from cycloaddition via an endo-transition state to the same kinetically formed dipole. In aryl imines of methyl phenylglycinate the kinetic dipole undergoes partial stereomutation giving ca. 3:1 mixtures of cycloadducts derived from the kinetic dipole and the stereomutated dipole. Structural assignments are based on 1H n.m.r. data including n.O.e. difference spectroscopy.
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