LENGTHENING OF THE CARBON-CHAIN OF SUGARS BY THE CH(NO2).CH(OET)2 FRAGMENT - A ROUTE TO HIGHER 2-AMINO-2-DEOXYALDOSES

Nitroaldol (Henry) reactions promoted by trialkylsilyl chlorides have been applied to the preparation of chain-extended nitro and amino sugars. The one-pot reaction of 1,2:3,4-di-O-isopropylidene-alpha-D-galacto-hexodialdo-1,5-pyranose (1) with 1,1-diethoxy-2-nitroethane in the presence of Et3N, Bu4NF .3H2O, and tBuMe2SiCl yielded 7-deoxy-1,2:3,4-di-O-isopropylidene-7-nitro-L-threo-alpha-D-galaCto-oc-todialdo-1,5-pyranose diethyl acetal (3a) and a diasteteoisomer in the ratio 4:1. The structure of 3a was established by a single crystal X-ray diffraction study. Hydrogenation of 3a (Ni, H-2) afforded the corresponding 7-amino-7-deoxy-1,2 : 3,4-di-O-isopropylidene-L-threo-alpha-D-galacto-octodialdo-1,5-pyranose diethyl acetal (4a). Conversion of the latter compound into a trans-oxazoline derivative demonstrated that the L-threo configuration had been retained. Likewise, reaction of the aldehydo sugar 1 with 1-nitropropane was carried out in order to compare the efficiency of the new nitroaldol procedure here applied with that reported using trialkylsilyl nitronic esters as intermediates.