SYNTHESIS OF STEREOPENTAD SUBUNITS OF ZINCOPHORIN AND RIFAMYCIN-S THROUGH USE OF CHIRAL ALLENYLTIN REAGENTS

The anti,anti adduct 3, from addition of the allenic stannane (P)-2 to the alpha-methyl-beta-OBn aldehyde (S)-1 promoted by SnCl4, was conve rted to the stereopentad 6 by a sequence involving reduction to the (E )-allylic alcohol with Red-Al, Sharpless asymmetric epoxidation, and a ddition of the higher-order methyl cyanocuprate to the derived epoxide 5. Stereopentad 6 was converted to the acetonide acetal 15, an interm ediate in Danishefsky's synthesis of zincophorin. By a similar sequenc e, adduct ent-4 was converted, via diol 19, to stereopentad 22, an int ermediate in Kishi's synthesis of rifamycin-S. An alternative route to diol 19 was achieved from the MOM-protected derivative 28 of epoxy di ol 18.