Total synthesis of a protected form of 2,6-anhydro-5-azido-3,5-dideoxy-2-C-hydroxymethyl-L-allo-heptose; a potential precursor of analogs of C-glycosides of neuraminic acid

The title aldehyde (-)-3 and its enantiomer (+)-3 have been prepared starting from furfuryl alcohol and acetone. The method involves the diastereoselective [4+3]-cycloaddition of 2-[(benzyloxy)methyl]furan and 1, 3-dibromo-2-oxyallyl cation giving adduct (+/-)-4 that was converted with high yield into (+)(2RS, 5RS, 6SR)- 5-azido -2-[(benzyloxy)methyl] -2, 3,5,6-tetrahydro-2, 6-bis (hydroxymethyl) -4H-pyran-4-one ((+/-)-9). Ketone (+/-)-9 was then transformed with high selectivity into (+/-)-(2RS,4RS,5SR,6RS)-5-azido-2-[(benzyloxy)methyl]-2, 3,5,6-tetrahydro-4-[(triethylsilyl)oxy]-6-{[(triisopropylsilyl)oxy]methy l}-2H-pyran-2-methanol (+)-3 that was resolved by the Alexakis-Mangeney method (column chromatography of aminals derived from (1R,2R)-1,2-diphenylethylenediamine). The absolute configuration of (-)-3 was established by circular dichroism and the Dale-Mosher method on derivatives. (C) 2001 Elsevier Science Ltd. All rights reserved.