Chemistry of L-Ascorbic Acid: Regioselective and Stereocontrolled 2-C- and 3-C-Allylation via Thermal Claisen Rearrangement

We report the convenient preparation of 3-O- and 2-O-allylated derivatives of 5,6-O-isopropylidene L-ascorbic acid (1) with various allyl substituents in high yield and their quantitative thermal Claisen rearrangement to the corresponding 2-C- and 3-C-allylated derivatives with high regio- and stereoselectivity under relatively mild conditions. This reaction will now allow the synthesis of heretofore unknown 3-C-allylated derivatives of L-ascorbic acid in high yield. The high chiral induction at the substituents of the allylic carbon, especially in the case of the 3-O-methyl-2-O-crotyl derivative, is intriguing. This general method of preparation of 2-C- and 3-C-allylated derivatives of ascorbic acid may have important applications in synthetic organic and pharmaceutical chemistry