Stereoselective synthesis of C24-hydroxylated vitamin D3 analogs: a practical and expeditius route to calcipotriol.

Abstract The synthesis of the clinically important drug calcipotriol ( 2 , MC903) is described as an example of a new and efficient approach to C24-hydroxylated analogs and metabolites of vitamin D 3 ( 1 ). The key step of the process is the generation of the C24 stereocenter by DAIB [(−)-3- exo -(dimethylamino)isoborneol]-catalyzed addition of the alkenylzinc derivative of alkyne 3 to cyclopropylcarboxaldehyde.