PHOTOCHEMISTRY OF HECOGENINE ACETATE REVISITED

We were successful in optimizing the synthesis of the homoallylic alco hol 6 from hecogenine acetate 2 as an important precursor for our appr oach to cephalostatin analogues by doubling the yields. On this way we discovered that formation of homoallylic alcohol 6 proceeds via a dia stereoselective intramolecular Lewis acid catalysed ene reaction direc tly from lumihecogenine acetate 3. Finally we were able to elucidate t he structure of the already described but not clearly identified oxa-d imer 7.