THE INTRAMOLECULAR NITRILE OXIDE CYCLOADDITION ROUTE TO FORSKOLIN

The ketone I, a potential precursor of forskolin (II), was prepd. in several steps from -damascone. A key step was the treatment of the Michael adduct III under Mukaiyama conditions to give 20% oxazole IV, which underwent acetalization and epimerization to give 55% acetal V. V was also obtained less directly, but more conveniently, from III by sequential redn., acetylation, intramol. cycloaddn., sapon., Moffatt oxidn., and acetalization.