Reductive opening of sugar epoxides by diborane-borohydride ion

Abstract

Carbohydrate epoxides were reduced selectively in the presence of sulfonyl ester, ketal, and acetal groups. Unlike more conventional reagents, such as aluminum hydride, alkoxyaluminum hydrides, and Raney nickel, this reagent permits the presence of a trans-(arylsulfony1)oxy group adjacent to the epoxide ring. The regioselectivity of the ring-opening reaction appears to be controlled primarily by the steric and polar factors. (11) (a) Baer, H. H.; Madumelu, C. B. Carbohydr. Res. 1975,39, C8. (b) Weissenberg, M.; Krinsky, P.; Glotter, E. J. Chem. SOC., Perkin Trans. I 1978, 565.Vinylmercuric chlorides readily react with rhodium(1) and rhodium(II1) catalysts and carbon monoxide to give excellent yields of divinyl ketones. The best reaction conditions are 0.5 mol % [Rh(CO),Cl], and 2 equiv of lithium chloride under 1 atm of carbon monoxide at room temperature. This rhodium catalyst also provides improved yields of diary1 ketones from arylmercurials at 70 "C under 1000-1500 psi of carbon monoxide pressure. Organorhodium compounds are presumed to be intermediates in these reactions.Divinyl ketones are employed in organic chemistry as and less frequently as singleg Michael acceptors.