ALPHA-HYDROGEN ELIMINATION IN SOME CARBOHYDRATE TRIFLATES

Treatment of 1,2;5,6-di-O-isopropylidene-3-O-triflyl-D-gluco- and D-al lo-furanoses (2 and 6) with MeLi (or BuLi) in diethyl ether afforded d ifferent products; the former gave a 3,4-unsaturated product (4), the latter a 3-methyl(or butyl)-D-allofuranose derivative (7, 8). Similar treatment of the 2-triflates (27, 30) of methyl 3-O-benzyl-4,6-O-benzy lidene-alpha- and -beta-D-gluco-pyranosides gave the corresponding 2-C -alkyl derivatives. The 3- and 4-triflates of similar pyranoside struc tures examined gave, in most cases, the corresponding unsaturated comp ounds. Both of the reactions (unsaturation and C-alkylation) are expla ined, in most cases, on the basis of alpha-elimination, that is, the r eactions commenced with abstraction of the hydrogen attached to the ca rbon bearing a triflyloxy group, this fact being confirmed by studies with deuterated analogs. Transition states for these reactions were al so studied by computer calculations. (C) 1996 Elsevier Science Ltd.