4,6-Benzylidene sugars

Reductions. Aldehydes. arom the presence of Bu,NF. Aluminum c reductive cleavage of 2-phenyl-1.3h1 from the 4,6-benzylidene sugars). ... 

Reductions. Aldehydes, aromatic acids and their esters are reduced by PMHS in the presence of Bu NF. Aluminum chloride is also an effective catalyst in the selective reductive cleavage of 2-phenyl-1,3-dioxanes and dioxolanes (e.g., 4-O-benzyl derivatives from the 4,6-benzylidene sugars).- ... 

The presence of hydroxyl groups in the benzylidene sugars does not interfere with the reaction and by-products are usually minor. Suitable solvents other than carbon tetrachloride, include benzene and tetra-chloroethane. Epoxide, amide, and other commonly encountered functionalities in sugar derivatives are unaffected under the reaction conditions. The corresponding 6-bromo-4-benzoates are valuable intermediates... 

The reaction involving 2,3-O-benzylidene sugars was then extended to a study of the behavior of 1,2-O-isopropylidene derivatives.272 Furanoid derivatives 262 and 263 gave, respectively, (+)-(S)-(E)-5-butyl-l-methoxy-3-nonen-2,5-diol (264) (yield 23%) and ( + )-2(R),3(S)-(E)-6-butyl-l,2-dimethoxy-4-decen-3,6-diol (265) (yield 21%). On the other hand, acetal derivatives of the D-arabino (266) and... 

Bemylidene-D-Erythrose.—The condensation of this benzylidene sugar with nitromethane80 constitutes the most satisfactory example of the reaction to date both with regard to yield of products and to the absence of marked epimeric preference in the formation of the two... 

Hanessian, S, Plessas, N R, Reaction of 0-benzylidene sugars with A-bromosuccinimide. HI. Applications to the synthesis of aminodeoxy and deoxy sugars of biological importance, J. Org. Chem., 34, 1045-1053, 1969. 

Hanessian, S, The reaction of O-benzylidene sugars with iV-bromosuccinimide, Carbohydr. Res., 2, 86-88, 1966. 

These methods have been applied to 1,2-0-benzylidene sugars and, in general good selectivity, can be achieved for cleavage at the anomeric side of the acetal to give the benzyl ether at the 2-positionA... 

O-benzylidene sugars is very valuable. Note that cleavage of benzyl esters with hydrosilane is catalyzed by PdfOAcli. ... 

Corey and Hase have found that 1,3-dithiolans and 1,3-dithians can be converted in good yields into dimethyl acetals, cyclic acetals, or thioacetals (or thioketals) upon reaction of the mono-5-methylated derivatives with methanol, ethylene glycol, and mercaptoethanol, respectively. These interchanges do not appear to involve the free carbonyl compound. The disulphonium salt prepared by the reaction of triethyloxonium tetrafluoroborate with 2-phenyl-l,3-dithiolan can be used to prepare benzylidene derivatives of 1,2-, 1,3-, and 1,4-diols (30— 80%) under basic conditions. This reaction appears to have considerable potential as a route to benzylidenated sugars. 

The 4,6-O-benzylidene group is also cleaved under these conditions, but the anomeric linkage between sugars is not affected. Anomeric trimethylsilyl-... 

Alkylation of enamines with epoxides or acetoxybromoalkanes provided intermediates for cyclic enol ethers (668) and branched chain sugars were obtained by enamine alkylation (669). Sodium enolates of vinylogous amides underwent carbon and nitrogen methylation (570), while vicinal endiamines formed bis-quaternary amonium salts (647). Reactions of enamines with a cyclopropenyl cation gave alkylated imonium products (57/), and 2-benzylidene-3-methylbenzothiazoline was shown to undergo enamine alkylation and acylation (572). A cyclic enamine was alkylated with methylbromoacetate and the product reduced with sodium borohydride to the key intermediate in a synthesis of the quebrachamine skeleton (57i). 

The Preparation of Bromodeoxy Sugars from O-Benzylidene Acetals... 

---