CHEMISTRY OF L-ASCORBIC-ACID - REGIOSELECTIVE AND STEREOCONTROLLED 2-C-ALLYLATION AND 3-C-ALLYLATION VIA THERMAL CLAISEN REARRANGEMENT

We report the convenient preparation of 3-O- and 2-O-allylated derivat ives of 5,6-O-isopropylidene-L-ascorbic acid (1) with various allyl su bstituents in high yield and their quantitative thermal Claisen rearra ngement to the corresponding 2-C- and 3-C-allylated derivatives with h igh regio- and stereoselectivity under relatively mild conditions. Thi s reaction will now allow the synthesis of heretofore unknown 3-C-ally lated derivatives of L-ascorbic acid in high yield. The high chiral in duction at the substituents of the allylic carbon, especially in the c ase of the 3-O-methyl-2-O-crotyl derivative, is intriguing. This gener al method of preparation of 2-C- and 3-C-allylated derivatives of asco rbic acid may have important applications in synthetic organic and pha rmaceutical chemistry.