The primary and secondary alcohols of the dipyranoses 6 and Sa are used as implements for elaborating the upper pyranoside rings of the tripyranoses 27 and 28, respectively. Compound 27 contains seven of the eight chiral centers of rifamycin S, while 28 fixes seven of the nine chiral centers of streptovaricin A. For the synthetic procedures, the primary alcohol is oxidized to an aldehyde, which is subjected to olefination with a phosphorane of ...
