NEW REACTIONS AND INTERMEDIATES INVOLVING THE ANOMERIC CENTER

The chemistry of new carbohydrate derivatives, involving the anomeric center and leading to glycosyl carbanions, radicals, radical anions, oxonium ions and to glycosylidene carbenes is presented. Derivatives generated on the way to 1-nitroaldoses involve hydroximolactones, halonitroso ethers and halonitro ethers. Hydroximolactones from spiro-isoxazolidines and some of their carbamates are enzyme inhibitors. Halonitroso ethers are reactive and diastereoselective dienophiles. Halonitro ethers from C,C bonds via radical anions. Nitroaldose-derived carbanions undergo 1,2- and 1,4-additions. In the products, the nitro group can be replaced by HO, RO, H, nucleobases and alkyl groups. Nitroaldoses form 1-nitroglycals. 1,4-addition of O-, N- and C-nucleophiles to 1-nitroglycals generate C(2) substituted carbanions which may react, inter- or intramolecularly, to chain-elongated or annelated products. The newly prepared alkoxydiaziridines (1-hydraziglycoses) rearrange to glyconolactone hydrazones and are oxidized to 1-aziglycoses, which react via glycosylidene carbenes. O-Benzylated 1-aziglycoses react preferentially with acidic hydroxy compounds to yield glycosides in a reaction which appears insensitive to steric hindrance and which allows regioselective glycosidations. Proton transfer to glycosylidene carbenes is evidenced by the formation of C-aryl glycosides as byproducts, of orthoesters from O-acylated and of oxazolidines from 2-acetamido derivatives. 1,2-trans O-arylglycosides are the main products from phenols. Participation of a C(2)-benzyloxy group is postulated and evidenced by the glycosidation of 1-azi-1,2-dideoxyglycoses. Spiro-cyclopropanes are formed from O-alkylated and from O-acylated 1-aziglycoses. Reaction with Ph2PH yields glycosylphosphines and, hence, phosphine oxides.