L. N. Domelsmith

Diels-Alder reactions between trans-1-N-acylamino-1,3-dienes and methyl acrylate. A correlation between diene photoelectron ionization potentials and reactivity, stereoselectivity, and regioselectivity

A quantitative study of the Diels-Alder reaction of a series of trans-N-acylamino-l,3-butadienes (1) and methyl acrylate is reported. The effect of the dienamide acyl substituent X on the rate, regioselectivity, and stereoselectivity of the cycloaddition reaction was determined. The photoelectron spectra of this series of dienes is also reported and analyzed. The relationship between these ionization potentials and theoretical Diels-Alder reactivities and stereoselectivities is summarized, and these theoretical estimates are compared with the experimental results. The Diels-Alder reaction is one of the best known and most useful organic reactions.2 It provides the synthetic chemist with one of his most powerful tools for constructing six-membered rings, and has a singular capability of establishing a large number of stereochemical centers in one synthetic step. Although the reaction has been successfully employed by chemists for decades, it is only within the last few years that a fundamental understanding of the reactivity, stereoselectivity, and regioselectivity phenomena of the Diels-Alder reaction has begun to emerge.3s4 Frontier molecular orbital theory, in particular when combined with quantitative experimental data about unsaturated systems, has proven notably successful in this regard.3 A variety of 1,3-dienes with N-acylamino substitution at either the 1 or the 2 position are available as a result of recent investigations in our l a b ~ r a t o r y . ~ These dienes are useful synthetic intermediates, and their application to solve stereochemical problems in the area of alkaloid total synthesis has been reported.6 In the parent 1,3-butadiene series, for example, trans1-N-acylamino substituted 1,3-butadienes (1) (a, X =

The relative rates of electron-rich and electron-deficient alkene cycloadditions to benzyne. Enhanced electrophilicity as a consequence of alkyne bending distortions.

Abstract Benzyne reacts more rapidly with electron-rich alkenes than electron-deficient alkenes, a result of the abnormally low energy LUMO of benzyne, which results from the acetylene bending enforced by the benzyne geometry.