Studies on Indian medicinal plants—XXXIX : Reinvestigation of the lactones and bromo derivative of betulinic acid

Isobornyloxy aluminium dichloride reduction of the ketolactone 2a of betulinic acid (1a) gave the axial alcohol 2b as the preponderant product. Hydroxylactone B of 1a therefore must have the equatorial OH function contrary to our previous conclusion. The so-called “hydroxylactone A” has been found to be the ring A rearranged product 3a. Reexamination of earlier work has shown that 1a yields a mixture of 2e and 5a in presence of HBr-AcOH, and a mixture of 2d and 3a with refluxing formic acid. Bromination of 1a affords 1e.