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.