Fujimoto–Belleau reaction

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.

The reaction can be employed in the syntheses of steroids such as cholestenone, testosterone, and cortisone.