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Branched-chain sugars reactions

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). [Pg.357]

Two branched-chain sugars, methyl 3-azido-4,6-0-benzylidene-2,3,-dideoxy-3-C-(fluoromethyl)-a-D-flraZ)/ o-hexopyranoside and methyl 2-azido-4,6-0-benzylidene-2,3-dideoxy-2-C-(fluoromethyl)-) -D-r/to-hexo-pyranoside have been prepared through the usual displacement reactions. [Pg.142]

The aqueous Heck coupling reaction was also used for the synthesis of unprotected branched-chain sugar. In the media of DMF-H2O (5 1) and the use of Pd(dba)2 and P(o-tol)3 the Heck reaction proceeded smoothly to give the coupling product with high yield (up to 84%) (Eq. 3.38).148... [Pg.74]

It has been suggested15 that apiose [3-(hydroxymethyl)-D-g cero-tetrose] (LVII), a branched-chain pentose,47 originates from the aldol reaction of dihydroxyacetone with glycolaldehyde. The origin of this and all other branched-chain sugars so far encountered in natural products is uncertain, but they may arise from intermediate branched-chain carboxylic acids which are believed to be formed in the fixation of carbon dioxide (see above). [Pg.237]

The general chemistry of branched-chain sugars has not been the subject of systematic investigation, mainly because of the scarcity of these compounds. Nevertheless, the totality of reactions employed for elucidating the unique structures of these compounds constitutes a body of valuable information which is basic for future developments. Lucid articles on the chemistry of streptose, by Lemieux and Wolfrom,1 and of apiose, by Hudson, have appeared in earlier volumes of this Series the present article will therefore not include information on these two sugars, except as regards comparison with other sugars and in reference to new developments. [Pg.264]

K. Sato and J. Yoshimura, Branched-chain sugars. XII. The stereoselectivities in the reaction of methyl 4,6-O-benzylidene-a- and -p-D-hexopyranosid-3-uloses with diazomethane, Bull. Chem. Soc. Jpn., 51 (1978) 2116-2121. [Pg.182]

B. Flaherty, S. Nahar, W. G. Overend, and N. R. Williams, Branched-chain sugars. XIV. Reactions of glycosulose derivatives with diazomethane. Ring expansion of glycosulose derivatives, J. Chem. Soc., Perkin Trans. I (1973) 632-638. [Pg.182]

The synthesis of type II branched-chain sugars should seem a more difficult task because it needs activation of a carbon atom on the sugar template and a control of the stereochemical course of the carbon-carbon bond formation. Probably because of this apparent difficulty several methods have been devised in the last decade, in particular, in the field of organo-metallic and free radical reactions. [Pg.215]

The recognition of the usefulness of radical reactions as a synthetic tool has prompted the exploration of this method for branched-chain sugars synthesis. Radical addition to an olefin is one of the most popular reactions yet investigated [10], Two approaches have been devised an intramolecular version, which is mostly a 5-exo cyclization and an inter-molecular version in which the radical is trapped by an activated olefin. [Pg.219]

Another route to create a carbon-carbon double bond on a ketosugar is the Knoevenagel reaction and its variants. It has been applied by Szarek and Ali to prepare olefin 133 (Scheme 45) suitable for the formation of a doubly branched-chain sugar [177] [see Section 1I.D]. [Pg.232]

Aldol reactions of sugar enolates have provided a good entry to C-C double bond branched-chain sugars [178]. As already mentioned, condensation of aldehydes, such as acetaldehyde or propionaldehyde, gives a mixture of aldol 120 of R,S configuration at the... [Pg.232]

M. L. Wolffom and S. Hanessian, Reaction of free carbonyl sugar derivatives with organo-metallics reagents. II 6-Deoxy-L-idose and a branched-chain sugar, J. Org. Chem. 27 2107 (1962). [Pg.252]

Carbohydrate chemistry is engaged in the synthesis and variation of deoxy sugar chains, where a wide set of protective groups and stereoselective glycosylation techniques are required. This contribution centers on stereoselective syntheses of mono-and oligosaccharides in the field of 2,6-dideoxy- and, in particular cases, branched-chain sugars, and summarizes modem synthetic glycosylation reactions which have been developed for this special kind of carbohydrate chemistry. [Pg.286]

J. Yoshimura, N. Kawauchi, T. Yasumori, K. Sato, and H. Hashimoto, Branched-chain sugars. 37. Synthesis of 2,3-anhydro-hexopyranosides and 3,4-anhydro-hexopyranosides having a methyl branch on the oxirane ring, and their reactions with some lithium methylcuprate reagents, Carbohydr. Res., 133 (1984) 255-274. [Pg.184]


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See also in sourсe #XX -- [ Pg.231 , Pg.250 ]




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Branched chain

Branched chain reactions

Branched-chain sugars

Branched-chain sugars Diels-Alder reaction

Branched-chain sugars Wittig reaction

Branched-chain sugars radical reactions

Branching chain reactions

Chain branching

Sugar, reactions

Sugars branched

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