A Facile Synthesis of 2,6-Dideoxy 6,6,6-Trifluorinated Carbohydrate Analogues

The syntheses of 2,6-dideoxy-6,6,6-trifluoro-DL-arabino-hexose (4) and the corresponding glycoside, ethyl 2,6-dideoxy-6,6,6-trifluoro-DL-arabino-hexopyranoside (11), are described. The key step in the synthesis of (4) involved the Lewis acid catalysed hetero-Diels–Alder reactions of (E)-4-benzyloxy-1,1,1-trifluorobut-3-en-2-one and benzyl vinyl ether. Hydroboration of the resulting cycloadduct, and hydrogenylitic debenzylation gave (4) in a 59% overall yield. The ethyl glycoside (11) was prepared in a similar manner from ethyl vinyl ether. A single-crystal X-ray diffraction study confirmed the structural assignment of (11). The O-glycosides (17) and (18) were formed from the boron trifluoride etherate promoted reaction of the per-acetate of (4), i.e. (16), and 2-naphthol. However, a similar reaction between 5-hydroxy-1,4-dimethoxynaphthalene and (16) gave the disubstituted C-glycoside (19) in 52% yield.