C-Vinyl glycosides

Further, the olefinic alcohols (11a and 11b) derived from an (l )-glyceraldehyde derivative, upon PdCl2- and Pd(OAc)2-mediated cyclization, gave hitherto important 2-deoxy C-alkyl (12) and C-vinyl glycosides (13), respectively, albeit as 1 1 mixtures, due to the absense of anchimeric assistance in stereodefining (Scheme 22.4). 

In the first total synthesis of (+)-ambruticin (59), the left-hand ring was derived from methyl a-D-glucoside, with the p-C-vinyl glycoside link being established by coupling of a tran -vinylalane with a glycosyl fluoride. 

Scheme 2 illustrates a general route to 2-deoxy-2-C-vinyl glycosides by way of a cyclopropanation of glycals. Other configurated sugars are described, giving rise to stereochemically different products. ... 

L. Cottier, G. Remy, and G. Descotes, Photochemical synthesis of O-vinyl glycosides and their transformation into C-branched sugars, Synthesis p. 711 (1979). 

Furthermore, coupling to form C-aryl glucals, as precursors to C-aryl glycosides, was carried out both from the C-metallated glucal154 and onto the C-iodo glucal (equations 90 and 91)155. A synthesis of vineomycinone B2 methyl ester has resulted from this chemistry. A vinyl-vinyl coupling reaction has also formed the cornerstone of aryl steroid synthesis (equation 92)156. 

In the presence of a Pd catalyst, CIPd[P(Cf,Hvinyl iodide couples with mctalatcd aromatics, particularly arylzinc chloride or arylboronic acids. Aryl Grignard reagents, however, couple in very low yield. The resulting C-aryl glucals can be converted to C-aryl glycosides by functionalization of the enol ether double bond.2... 

Several C-glycosylated amino acids were obtained by 13-DC of (-)-menthonc-derived chiral nitrone (-)-90 and allyl- or vinyl glycosides. For instance the cycloaddition of (-)-90 and 91 occurred with complete diastereo- and regioselectivity to afford the isoxazolidine 92 in 92% yield. The a-amino acid moiety was then obtained by Sm(ll) mediated cleavage of the N-O bond followed by fV -acetal and amide hydrolysis <01OL1375>. 

C-(P-ketoalkyl) glycosides 43, 773 vinyl glycosides 43, 184 a-Glycosyl halides... 

Me glycoside, 4,6-benzylidene Methyl 4,6-0-benzylidene-2,3-dideoxy-2-C-vinyl-a-D-erythio-hex-2-enopyranoside [117514-02-0]... 

Sugar-derived /,5-unsaturated alcohols can he efficiently transformed into C-vinyl furanosides using an oxidative cyclization procedure (eq 75). Thus, treatment of a DMSO solution of the relevant substrate with catalytic quantities of Pd(OAc)2, sodium acetate and oxygen provides the expected cyclization products which serve as precursors to C-linked amino acids and glycosides. " ... 

---