Decarbonylation of unprotected aldose sugars by chlorotris(triphenylphosphine)rhodium(I). A new descent of series approach to alditols, deoxyalditols, and glycosylalditols

Unprotected C{sub n} aldose sugars are cleanly decarbonylated by 1 equiv of chlorotris(triphenylphosphine)rhodium(I) in 1-24 h at 130{degree}C in N-methyl-2-pyrrolidinone solution to give the corresponding C{sub n{minus}1} alditol in about 75-95% yields. This technique represents a useful variation on traditional carbohydrate descent of series reactions. The procedure is quite general and also works on a number of aldose derivatives, such as deoxy sugars, N-acetylated amino sugars, and disaccharides, providing convenient small-scale syntheses of deoxyalditols, (acetylamino)-deoxyalditols, and glycosylalditols, respectively. The reactions proceed with complete retention of stereochemistry, the only side products observed being a few percent of the C{sub n} lactones and the C{sub n{minus}2} alditol. Attempts to make the reactions catalytic have not yet been very successful.