Enantioselective total synthesis of (+)-colletoic acid via catalytic asymmetric intramolecular cyclopropanation of an α-diazo-β-keto diphenylphosphine oxide

The enantioselective total synthesis of (+)-colletoic acid, a potent naturally occurring 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) inhibitor, is described. This total synthesis features a highly enantioselective catalytic asymmetric intramolecular cyclopropanation of an α-diazo-β-keto diphenylphosphine oxide and five highly stereoselective reactions (cyclopropane opening, Diels-Alder reaction, iodolactonization, alkene formation, and reduction of α,β-unsaturated carboxylic acid).