Fujimoto–Belleau reaction

The Fujimoto–Belleau reaction is a chemical reaction that forms cyclic α-substituted α,β-unsaturated ketones from enol lactones. The reaction was discovered in 1951 by George I. Fujimoto and Bernard Belleau. Belleau used this reaction to synthesize 1-methyl-3-keto-1,2,3,9,10,10a-hexahydrophenanthrene from a ketoacid starting material and Fujimoto demonstrated that steroids could be synthesized from naturally occurring lactone species using this method as well.

The reaction starts with opening the ring by the attack of the Grignard reagent, forming an enolate. A proton transfer occurs, forming another enolate via deprotonation of the carbon atom attached to the R group. Using the enolate, an aldol condensation then occurs with aqueous or acidic workup—i.e., aldol addition followed by an E1cB elimination of hydroxide occurs.