Brønsted acid-catalyzed stereoselective allylation of exo-glycals with allyltrimethylsilane
Quaternary stereocenter on carbohydrate scaffolds is an important motif due to its presence in natural products and biologically active compounds. However, the preparation of C,C-glycosides is a challenge, and to date, many studies have failed to exploit exo-glycals as starting materials. The allylation methodologies of sugar lactol and sugar lactone starting materials suffer from poor regio- and stereoselectivity. Recently, we have developed a synthetic method for the allylation of exo-glycals using allyltrimethylsilane. This Brønsted acid-catalyzed transformation for the preparation of C,C-glycosides occurs readily in the presence of a tetrafluoroboric acid diethyl ether complex. In contrast to previously reported procedures, this reaction proceeds in a diastereoselective manner to afford α-allyl substituted pyranose.