Lengthening of the carbon chain of sugars by the Ch(NO 2·CH(OEt) 2 fragment a route to higher 2-amino-2-deoxyaldoses

Abstract

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-isopropylidine-α- d- galacto-hexodialdo-1, 5-pyranose ( 1) with 1,1-diethoxy-2-nitroethane in the presence of Et 3N, Bu 4NF ·3H 2O, and tBuMe 2SiCl yielded 7-deoxy-1,2:3,4-di- O-isopropylidene-7-nitro- l- threo-α- d-galacto -octodialdo-1, 5-pyranose diethyl acetal ( 3a) and a diastereoisomer 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-7deoxyl-1,2:3,4-di- O-isoprpylidene- l- threo-α- 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.