SYNTHESIS OF (+ -)-AZAASCORBIC ACID

The synthesis of the hitherto unknown aza analog of ascorbic acid (+/- )-10a is described. Aldol type reaction of the tetramic acid derivativ e 4 with tert-butyldimethylsilyloxy acetaldehyde furnished a mixture o f the aldol (+/-)-5b and the diastereomeric O-Boc protected aldols (+/ -)-6a and (+/-)-6b. By X-ray structural analysis the major reaction pr oduct was shown to be the three isomer 6a. Desilylation of 6a led to t he alcohol 7. Removal of the remaining protective groups yielded racem ic azaascorbic acid 10a. Similar deprotection of the aldol 5b led only to impure azaisoascorbic acid (+/-)-10b which was characterized as th e dimethyl ether 12b.