Preparation of Stabilized Phosphorus Ylides via Multicomponent Reactions and Their Synthetic Applications

Triphenylphosphine (TPP), dialkyl acetylenedicarboxylates (DAAD), and acids such as phenols, imides, amides, enols, oximes and alcohols react with each other via a multicomponent reaction to produce stabilized phosphorus ylides. The reactions take place easily, through formation of intermediate formed by the Michael addition of the triphenylphosphine to dialkyl acetylenedicarboxylates and concomitant protonation of the intermediate by an acid leads to vinyltriphenylphosphonium salts. The salts are unstable intermediates and undergo a subsequent Michael addition leads to stabilized phosphorus ylides. In some cases ylide products are stable, but in other cases they cannot be isolated and appear to occur as intermediates on the pathway to an observed product. The stabilized phosphorus ylides are able to take part in the normal intramolecular Wittig reactions and produce a variety of heterocyclic or carbocyclic compounds, but they are not able to participate in the intermolecular Wittig reactions.