Level 2 — Case 18 Unusual Diels-Alder Reactivity of Acyclic 2-Azadienes

Abstract

Azadiene 1, bearing an electron-withdrawing substituent (CO2Me), is expected to be electron-deficient and, therefore, more likely to react with electron-rich dienophiles in an inverse electron demand Diels-Alder reaction. However, for a diene, 1 shows a very unusual reactivity, since it participates in cycloadditions with both electron-rich and electron-deficient dienophiles. As an example, reaction of azadiene 1 with diethyl fumarate yields pyridine 2 whereas in the presence of N-cyclopenten- 1-ylpyrrolidine, tetrahydropyridine 3 is obtained (Scheme 18.1).