Zinc tetrafluoroborate catalyzed α-stereoselective synthesis of pseudoglycals: efficient synthesis of digitoxin α-l-amicetose†

We report here an efficient, fast, and cost-effective strategy for synthesizing pseudoglycals by the reaction of glycals with alcohols or nucleophiles using zinc tetrafluoroborate. This mild, transition metal-free approach allowed the α-selective synthesis of pseudoglycals using a wide range of acceptors containing various protecting groups/functionalities. This method is exemplified by the synthesis of digitoxin α-L-amicetose, a known potential cardiac glycoside anticancer agent. The improved 3-step synthesis from L-rhamnal afforded an overall yield of 54%, thus representing a significant improvement over the previous method.