Dithioacetals aldehydo Sugars

Closely similar results were obtained with various diphenyl dithioacetal acetates (7), with the unsubstituted diethyl dithioacetals (8), and with the aldehydo-pentose peracetates (9) and the tetra-O-acetylaldo-pentose dimethyl acetals (10). Subsequent work in other laboratories has shown the same general principles for the methyl 5-hexulosonates (11) and the pentononitrile tetraacetates (12), two examples where a full series of stereoisomers has been studied. Other workers have investigated isolated examples or partial series (13, 14, 15, 16, 17, 18), and parallel work by x-ray crystallography (19, 20, 21, 22) on acyclic sugar derivatives in the solid state has shown excellent correlation with the general principles outlined here for the molecules in solution. 

The pentoses may be converted by the conventional sequence (5) of dithioacetal formation, acetylation, and demercaptalation into the respective aldehydo-oentose 2,3,4,5-tetraacetates, which afford by Wittig chain-extension (2) the desired dienophiles. Thus aldehydo-D-arabinose 2,3,4,5-tetraacetate reacted with Ph3PCHC02Me in boiling benzene to give 90% of the pure, crystalline E-unsaturated sugar derivative 6, and the corresponding enantiomer was likewise prepared from L-arabinose. 

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