Diels-Alder Reactions in Micellar Media

Abstract

I. INTRODUCTION TO DIELS-ALDER REACTIONS The Diels-Alder reaction is a [4+2]cycloaddition in which a diene (four-π component) reacts with a dienophile (two-π component) to provide a six-membered ring (Fig. 1). Six new stereocenters are formed in a single reaction step. Because the conformations of the double bonds are usually fully retained, the reaction is stereospecific and consequently the absolute configuration of the two newly formed asymmetric centers can be controlled efficiently. The Diels-Alder reaction is of great value in organic synthesis and is a key step in the construction of compounds containing six-membered rings [1]. A historic account of this important conversion has been published by Berson [2]. Homo Diels-Alder reactions involve only hydrocarbon fragments. If the diene or dienophile possesses heteroatoms in any of the positions a-f (Fig. 1), heterocyclic ring systems are formed (hetero Diels-Alder reactions). Normal electron demand Diels-Alder reactions are promoted by electron-donating substituents in the diene and electron-withdrawing substituents in the dienophile. The opposite situation applies for inverse electron demand Diels-Alder reactions. Neutral Diels-Alder reactions are accelerated by both electron-withdrawing and electron-donating substituents.