Synthesis of 2-deoxy-2-c-alkyl glycal and glycopyranosides from 2-hydroxy glycal ester.

A method to convert 2-hydroxy glycal ester to the corresponding 2-deoxy-2-C-alkyl glycal in a facile manner, through key reactions including (i) C-allylation at C-1, (ii) Wittig reaction, and (iii) Cope rearrangement of a 1,5-diene derivative, is reported. The α-anomer of the 1,5-diene derivative underwent Cope rearrangement to afford 2-deoxy-2-C-glycal derivative, whereas the β-anomer was found to be unreactive. Employing this sequence, 3,4,6-tri-O-benzyl-2-O-acetyl-1,5-anhydro-d-arabino-hex-1-enitol was transformed to 3,4,6-tri-O-benzyl-2-deoxy-2-C-alkyl-1,5-anhydro-D-arabino-hex-1-enitol. 2-Deoxy-2-C-alkyl glycal derivative is a suitable glycosyl donor to prepare 2-deoxy-2-C-alkyl glycosides, mediated through haloglycosylation and a subsequent dehalogenation. A number of 2-deoxy-2-C-alkyl glycosides, with both glycosyl and nonglycosyl moieties at the reducing end, are thus prepared from the glycal.