Preparation of ginkgolide and F-seco-ginkgolide lactols: the unique reactivity of α-hydroxy lactones toward NaBH4

It has been found that NaBH4 smoothly reduces the α-hydroxy-lactone moieties in ginkgolide and F-seco-ginkgolides to lactols. The reaction is rapid and stops at the lactol stage; the coordination of NaBH4 to the conformationally rigid cage structure is involved in both the initiation and termination stages. This facile reduction of ginkgolide lactones yields a variety of new ginkgolide lactols.