Phosphoramidites Are Efficient, Green Organocatalysts for the Michael Reaction. Mechanistic Insights into the Phosphorus-catalyzed Michael Reaction of Alkynones and Implications for Asymmetric Catalysis

Hexamethylphosphorous triamide (HMPT) and other phosphoramidites and phosphites have been found to be efficient catalysts for the Michael reaction of alkenones and alkynones with malonates, alpha-cyano esters, beta-keto esters, and nitro compounds. The relatively nontoxic, easily hydrolyzed HMPT catalyzes the Michael reaction within seconds at room temperature in the absence of a solvent, and the reaction is worked up simply by removing the catalyst in vacuo. The Michael reactions of alkynones, unlike those of alkenones, are shown to be irreversible. The implications for asymmetric catalysis are discussed.