Synthesis of unsymmetrical 1,4-diethers of butadiene. A ready access to normal and ether-type disaccharides with the β-gulo-configuration

Abstract

The Wittig condensation of 3-benzyloxyacrolein with the phosphorane ROCHPPh₃ derived from ‘diacetoneglucose’ RO·H, gives in the presence of iodide ions and excess of bases a 78 : 22 mixture of the all-trans-(2) and 1,2-cis-3,4-trans-(3) unsymmetrical 1,4-diethers of butadiene, RO-CH:CH·CH:CH·O·CH₂Ph. From the cycloaddition products of L-menthy, glyoxylate onto the diene (2), three 1,4,5-trisubstituted 2,3-dihydro-6H-pyrans with the all-cis-disposition, (4)(13.5%), (6)(24%), and (8)(19%) could be isolated. These were converted in good yield into completely functionalized disaccharides by lithium aluminium hydride reduction of the ester function, followed by cis-hydroxylation with osmium tetraoxide. Thus were obtained, starting respectively from compounds (4) and (6), 3-O-(4-O-benzyl-β-D- and L-gulopyranosyl)-1,2;5,6-di-O-isopropylidene-α-D-glucofuranose, (10) and (12). On the other hand, compound (8) gave O-(benzyl 4-deoxy-β-D-gulopyranosid-4-yl)-(4→3)-1,2;5,6-di-O-isopropylidene-α-D-glucofuranose (14). Thus binding of the oxygen atom of the dienophile to the diene (2) occurs on the sugar side, to give compounds (4) and (6), with the β-D- and β-L-sugar configuration, and on the benzyl side to give an ether of a benzyl β-D-hexopyranoside (8). The introduction of a 4-benzyloxy-substituent does not appear to change the relative reactivity towards cycloaddition of the two faces of the buta-1,3-dien-1 -yl ether of ‘diacetone-glucose’.