Mannose dithioacetal, preparation

Methods of chain extensions generally use linear sugars with free aldehydes mostly prepared via dithioacetal formation, protection of the remaining hydroxyl groups and aldehyde recovery. This allows one to use all methods applicable to aldehydes. Among others, the condensation of ethyl diazoacetate has been studied in detail by L6pez-Herrera [207] in a new synthesis of KDO by a two carbon homologation of an open-chain mannose derivative. 

D-Arabinose 88 l-Deoxy-l,l-bis(ethylsulfonyl)-D-mannitol (1 g) (prepared by oxidation of D-mannose diethyl dithioacetal with peroxypropionic acid in dioxan) is made into a slurry with water (10 ml), and then concentrated aqueous ammonia solution (1 drop) is added. The sulfone dissolves rapidly and after 30 min the precipitated diethyl methylene disulfone is filtered off. The filtrate is extracted four times with chloroform (10-ml portions), and the aqueous phase is evaporated in a vacuum at 40°. The residue is treated with hot methanol (5 ml) and after being kept for 24 h at 4° affords / -D-arabinose (0.32 g, 86%), [a]D20 —102° (c 3.5 at equilibrium in water). 

The cyclohexylidenation of D-mannose diethyl dithioacetal aimed at the preparation of the fully 0-protected aldehydo-D-ma.nnose derivative 8 has been described. ... 

The diastereoisomeric 1-phenylethyl dithioacetals of arabinose, lyxose, fucose, rhamnose, galactose, glucose and mannose have been prepared and separated conventionally. 

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