A stereospecific pathway for the introduction of deuterium on the brassinosteroid skeleton by reductive dechlorination of chlorocarbonates

A new and efficient procedure for the preparation of brassinosteroids labeled with hydrogen isotopes was developed. A four-step reaction sequence started with the selective oxidation of a 2,3-diol group to an α-hydroxy ketone, which was converted stereospecifically into a chlorocarbonate by reaction with triphosgene. A subsequent Pd-catalyzed reductive dechlorination with deuterium gas yielded deuterium-labeled brassinosteroid 2,3-carbonates. The reaction sequence was completed by base-catalyzed hydrolysis of the cyclic carbonate.