Glycosides by addition

Glycosides 5c, 5d and 5g together with glycosides 6, Fig. (6) and 7, Fig. (7) are characterized by additional acetoxy or hydroxy groups in the side chain. 

The tin hydride method is very valuable for forming a C-C bond by addition of a radical to a C-C multiple bond in intermolecular or intramolecular systems [1,10,11]. Since the general principles of the chain reaction are known, this method is easy to apply. Therefore, one can design the reaction conditions carefully, taking into account the rates of the competing reactions and how the reactivity of the radical and the alkene can be influenced by substituents. Actually, formation of C-glycosides is the first example of the tin hydride method [12,13]. 

Somewhat surprisingly, particularly in view of the proposed means of formation of the glycosid-3-ulose derivative 2,1,5-anhydro-2,3,4,6-tetra-O-benzoyl-D-arah/no-hex-1 -enitol (tetra-O-benzoyl-2-hydroxy-D-glucal) does not undergo bromination at the allylic C-3 atom the only products isolated following attempted photobromination with N-bromosucdnimide were two dibromides produced by addition reactions.50... 

Correlation of nucleophilic rate data for phenyldimethylsulfonium ions with common nucleophiles, with pX e values shows that the slopes of the lines, jS[ e, correlate qualitatively with the Edwards hardness parameter for the nucleophile and not with the Swain-Scott n parameter.144 cw,cw-2,4,6-Trimethyl-l,3,5-triaminocyclohexane is weakly basic in aqueous solution, because of steric inhibition to solvation of the conjugate acid.145 The three NH2 groups are axial and the steric effect also results in reduced reactivity as a nucleophile in, S n2 reactions. Highly stereoselective syntheses of N-. and O-glycosides have been carried out by addition of anionic nucleophiles to glycosyl iodides.146 5 n2 reactions are involved, but some substrates are susceptible to E2 elimination when treated with highly basic anions. 

Chalcones and Pihydrochalcones. Chalcones and dihydro-chalcones are Intensely sweet compounds (39) that are effective in raising the threshold at which the bitterness of naringin and limonin is perceived (46). As illustrated in Figure 5, chalcones are easily formed fromTlavanone glycosides by the addition of alkali and dihydrochalcones are formed from hydrogenated chalcones. Like the flavanone neohesperidosides, the chalcones and dihydrochalcones vary in the intensity of their taste response. 

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