Organoalane-mediated isomerization of ascorbic and isoascorbic acid derivatives

Article abstract of DOI:10.1016/0957-4166(96)00427-2

Derivatives of L-ascorbic acid 2a, 10a/11a and D-isoascorbic acid 2b, 10b/11b, when treated with triisobutylaluminium, partly epimerize to give the corresponding derivatives of L-isoascorbic acid ent-2b, ent-10b or D-ascorbic acid ent-2a, ent-10a, ent-11a, respectively. Complete removal of the protecting groups is effected by hydrogenolysis of the benzylidene acetals ent-10 and ent-11a. This reaction leads to D-ascorbic acid ent-1a or L-isoascorbic acid ent-1b, respectively. Furthermore, the four acetonides 2 were converted by ozonolysis, transesterification and finally catalytic hydrogenation to the threonic and erythronic acid ketals 9. Copyright (C) Elsevier Science Ltd.