Synthesis of Alfaprostol Key Intermediate Ynol via Br/Mg Exchange

Abstract

We have developed an improved approach to the protected Corey lactone bromoalkyne with a significant increase in yield (35% and 37% in four steps) in comparison with our previous approach (18% over five steps). These compounds serve as starting materials for a novel, simple and reliable synthesis of alfaprostol key intermediate ynol via Br/Mg exchange (72%). The stereoselective effect of BINOL was investigated. We found that influencing stereoselectivity is possible; as to the matter of the S/R isomer ratio, however, a significant reduction in yield of targeted intermediates was observed.