SYNTHESIS OF UNSYMMETRICAL 1,4-DIETHERS OF BUTADIENE - READY ACCESS TO NORMAL AND ETHER-TYPE DISACCHARIDES WITH THE BETA-GULO-CONFIGURATION

The Wittig condensation of 3-benzyloxyacrolein with the phosphorane ROCH=PPh3 derived from 'diacetoneglucose' ROH, 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-menthyl 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'.