4? Participation of 1-Aza-1,3-butadienes in Cycloaddition Reactions: Intramolecular Diels-Alder Reactions of α,β-Unsaturated N-Sulfonylimines

Article abstract of DOI:10.1021/jo00060a022

The 4? participation of α,β-unsaturated N-sulfonylimines in intramolecular Diels-Alder reactions with unactivated dienophiles is detailed in studies which further extend the scope of the <4 + 2> cycloaddition reactions of this new class of 1-aza-1,3-butadienes.Similar to observations made in the intermolecular <4 + 2> cycloaddition reactions, a strong endo diastereoselectivity (>20:1) was observed to dominate in the cycloaddition reaction of 5b versus 5a and 5c.This endo specific reaction may be attributed to the combination of a pronounced, stabilizing secondary orbital interaction and preferred cycloaddition through an anti-endo transition state in which the lone pair on nitrogen and the C-aryl bond of the dienophile lie trans periplanar to one another benefiting from stabilization analogous to the ground-state anomeric effect.