Chiral lithium amide base-mediated rearrangement of bis-protected meso-4,5-dihydroxy cyclohexene oxides:: enantioselective synthesis of (4R,5S)- and (4S,5R)-4,5-bis(tert-butyldimethylsilyloxy)cyclohex-2-enone

The asymmetric synthesis of(4R,5S)- and (4S,5R)-4,5-bis(tert-butyldimethylsilyloxy)cyclohex-2-enone are described, Such bis-protected enones are useful intermediates in synthesis, and compounds with (4S,SR)-stereochemistry have previously been prepared from D-(-)-quinic acid, This paper reports the first synthesis of enones with (4R,SS)-stereochemistry. The route to the bis-protected enones involves chiral base-mediated rearrangement of meso-cyclohexene: oxides to allylic alcohols followed by PDC oxidation, Two new chiral base reactions are described: rearrangement of a trans-epoxide generates an allylic alcohol of 76% ee (93% yield) whilst that of a cis-epoxide produces an allylic alcohol of 92% ee (38% yield); suggestions for the observed differences in yield and enantioselectivities are proposed.