A-Allyl glycosides

C-Alkyl glycosides are useful carbohydrate mimetics, commonly employed as enzyme inhibitors. The formation of various C-alkyl glycosides was evaluated with phosphates 9 and 12 (Table 3). Mannosyl phosphate 9 was activated with TMSOTf and coupled to allyltrimethylsilane to provide a-allyl glycoside 2 (18) in excellent yield (93%). Coupling of 9 to the cyclopentanone derived trimethylsilyl enol ether 35 afforded 34 as a mixture of diastereomers in 84%... 

A novel latent-active glycosylation strategy was reported. This strategy is based on a rhodium-catalyzed isomerization of substituted allyl glycosides followed by a Lewis acid-mediated glycosylation reaction (Scheme 46).76 77... 

Therefore, taking into account the potentialities of such lactones as carbohydrate delivery synthons (vide infra), several routes leading to carboxymethyl glycosides (and thus subsequently to the lactones) were investigated, in order to get as many structural variations as possible for widening the scope of their use in synthesis. In addition to the isomaltulose oxidation method (route a), the oxidation of allyl glycosides (route b), and the anomeric alkylation with tert-butylbromoacetate (route c) were studied (Scheme 11). These three methods are detailed in the following sections. 

C-Allyl glycosides can be prepared by the reaction of glycal epoxides with allyltributyltin in the presence of tributyltin triflate as a Lewis acid,281 and aldonitrones can be allylated with trimethylsilyl triflate as a catalyst (Equations (101) and (102)).282... 

For a related addition of an allyl Grignard to a methyl glycoside see Danishefsky, S. DeNinno, M. Tetrahedron Lett., 1985, 823. 

Compound 10 was converted into allyl glycoside 11 in 73 yield in two steps, (a) Bu2Sn0CH2CH=CH2—SnCl,(4), and (b) MeONa—MeOH. Treatment of 11 with dimethoxypropane and TsOH, and then with benzyl bromide— NaH—DMF afforded compound 12 in 51% yield. Solvolysis of compound 12 in MeOH—AcOH, and then monobenzylation by the stannylation— alkylation method(5) gave the desired glycosyl acceptor 8 in 67% yield. Acetylation of compound 8 and then deallylation with PdCl2— AcONa in aq.AcOH(6) afforded a 93% yield of hemiacetal 13, which was treated with (a) SOCI2—DMF in dichloroethane(7) and (b) AgF— CH CN(8) to give the desired fluoride 9 in 73% overall yield. 

The allyl glycosides have been synthesized from allyl alcohol and the free carbohydrate, or the per-O-acetylglycosyl halide in the presence of acid, or mercury cyanide, as the catalyst. The condensation of the alcohol occurs with both anomers of the carbohydrate, and a mixture of the a- and /3-glycosides is obtained. The anomers can be separated by preferential, solvent extraction,12 or by chromatography on... 

The first investigation to realize a C-glycosidation through a cyclization reaction has been conducted by using the 3-allyl-3-deoxyglucose derivative 56 [28], The formation... 

---