2,3-Unsaturated glycosides, synthesis

F E R R I E R Chiral cyclohexanone synthesis Transtormatlon o< unsaturated glycosides into cyclohexanone derivatives by heating in aqueous acetone with mercury (II) salts... 

Iodo compounds were utilized in a further, new synthesis of unsaturated glycosides of this series. Thus, treatment of methyl 3,4,6-tri-0-acetyl-2-deoxy-2-iodo-/3-D-glucopyranoside and the a-o-manno isomer with sodium cobalt tetracarbonyl and carbon dioxide in ether caused eliminations, and afforded methyl 4,6-di-0-acetyl-2,3-dideoxy-/3- and a-D-ert/t/iro-hex-2-enopyranoside, respectively.80,1... 

A RUCI3 3H2O catalyst has been reported for the synthesis of 2,3-unsaturated-glycosides (Scheme 165). " ... 

Claisen rearrangement of 3,4-unsaturated glycosides to C4-branched derivatives provided useful intermediates for the total synthesis of thromboxanes (Scheme 20). First reported independently by Corey et al. [41] and Hernandez [42],both the Eschenmoser amide acetal and the Johnson orthoester procedure afforded good results for the conversion of allylic alcohol 99 (R = Me, R = H) to the respective amide or ester 100. Corey et al. further transformed the former compound to lactone 101, previously described as a precursor for the total synthesis of thromboxane B2 (102). A number of further derivatives 100 (R = allyl, R = H or TBDMS, R = NMe2 or OEt) and its C2-epimer were prepared in a similar manner during later thromboxane synthetic studies [43,44]. 

Aiming at the total synthesis of the antibiotic and antitumor agent nogal-omycin, Vatele [47] studied the Claisen rearrangement of 4,5-unsaturated glycosides 107 and 109 as an efficient method for the stereoselective formation of a quarternary chiral center (Scheme 22). The a, -unsaturated ester 110 was formed by elimination of the sulfinyl group subsequent to rearrangement of ke-tene acetal 109. 

Unsaturated compounds continue to be of value in glycoside synthesis - see some examples given in Chapter 13. 

P. Tiwari, G. Agnihotriand, and A. K. Misra, Synthesis of 2, 3-unsaturated C-glycosides by HC104-Si02 catalyzed Ferrier rearrangement of glycals, Carbohydr. Res., 340 (2005) 749-752. 

Fig. 30 Synthesis of 2,3-unsaturated allyl glycosides or glycosyl cyanides...

A base-catalyzed, elimination reaction was a key step in a synthesis of D-ribose from L-glutamic acid.188 In that work, L-glutamic acid was converted, by a series of reactions, into 5-0-benzyl-2,3-dideoxy-D-glycero-pentofuranose (157) from compound 157, a mixture of glycosides was obtained which, on treatment with bromine and calcium carbonate, gave the monobromo derivative 158 as a mixture of diastereoisomers. Base-catalyzed dehydrobromination of 158 afforded the unsaturated derivative 159. Hydroxylation of 159 with potassium permanganate or with osmium tetraoxide gave a mixture of methyl 5-0-benzyl-/3-D-ribofuranoside and methyl 5-O-benzyl-a-D-lyxofuranoside. 

J. Herscovici, S. Delatre, and K. Antonakis, Enantiospecific naphthopyran synthesis by intramolecular Diels-Alder cyclisation of 4-keto 2,3-unsaturated C-glycosides, Tetrahedron Leu. 32 1183 (1991). 

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