REACTION OF TETRA-O-ACETYL-ALPHA-D-HEXOPYRANOSYL BROMIDES WITH SODIUM PARA-NITROPHENOXIDE IN N,N-DIMETHYLFORMAMIDE - FORMATION OF PARA-NITROPHENYL 2,3,4,6-TETRA-O-ACETYL-BETA-D-HEXOPYRANOSIDES VERSUS 2,3,4,6-TETRA-O-ACETYL-1,5-ANHYDRO-D-HEX-1-ENITOLS

The reaction of the four acetylated hexopyranosyl bromides (d-allo, d-gluco, d-gulo, and d-galacto) with sodium p-nitrophenoxide in N,N-dimethylformamide was investigated in order to determine their tendency for displacement at C-1 (to form the p-nitrophenyl 2,3,4,6-tetra-O-acetyl-β-d-hexopyranoside) or β-elimination (to give the 2,3,4,6-tetra-O-acetyl-1,5-anhydro-d-hex-l-enitol). The tendency for the formation of tetra-O-acetyl-1,5-anhydro-d-hex-l-enitols decreased in the following order: d-allo > d-gulo ≳ d-gluco > d-galacto, whereas the preference for the formation of p-nitrophenyl tetra-O-acetyl-β-d-hexopyranosides was in the reverse order (d-allo < d-gulo ≲ d-gluco < d-galacto). The conformations of the four tetra-O-acetyl-1,5-anhydro-d-hex-l-enitols (d-ribo, d-arabino, d-xylo, and d-lyxo) were determined from their 250-MHz >1H-n.m.r. data; the d-lyxo derivative was determined to exist in the H54(d) conformation, whereas the H45(d) conformation was demonstrated for the other three isomers. The yields of the four tetra-O-acetyl-1,5-anhydro-d-hex-l-enitols were found to be directly related to factors governing the stability of their conformations. © 1979.