Olefinic sugar

Schiff base complexes to aromatic silyl enol ethers/ " olefins/ sugars,Mn ° Schiff base complexes, " and rhenium(III) complexes " has been reported. Similar reactions are observed with the Mn (N)porphyrin complexes. The reaction products are dependant on the nature of the Schiff base ligand, both the yield and the enantiomeric excess being affected. " Salen nitridomanganese(V) complexes have been incorporated into Zeolite... 

Systematic studies of the dicyclopropanation of olefinic sugars have been published [194], Dichlorocarbene, generated under phase-transfer catalysis reacts with 2,3-unsaturated pyranosides, such as 161 to yield a single isomer of the expected cyclopropane 162 (Scheme 55). A typical procedure is given in Section IE. The reaction is also possible with an enol... 

Ketones are known to be usually unreactive towards resonance-stabilized phosphoranes, excluding ethoxycarbonylmethylenetriphe-nylphosphorane.z(f) L-Sorbose pentaacetate was, however, reported51 to react, although incompletely, with acetylmethylenetriphenyl-phosphorane and certain aroylmethylenetriphenylphosphoranes, giving branched-chain, olefinic sugars (69) in about 25% yield. 

Many examples have been presented for the generation of olefinic sugar derivatives. Given that olefins provide useful handles for further functionalization, discussion centered on the reduction of these compounds is warranted. In this section, both catalytic and boron-based reductions are addressed. 

Paulsen, H., and Bartsch, W., Phosphorus-containing carbohydrates. Part 12. Preparation of olefinic sugar phosphonates and allenic sugar phosphonates, Chem. Ber., 108, 1732, 1975. 

It has been claimed3 that no selectivity is observed in ethyl acetate, but, in recent work (see Section IV,2c, p. 128) selective hydrogenations have been achieved by using this solvent. Sodium borohydride in ethanol has also been found9111 to reduce the double bond of nitro-olefinic sugars selectively. 

An interesting study has been made of the photolysis of a nitro-olefinic sugar.148b Irradiation, at 253.7 nm, of an acetone solution of cis-6,7,8-trideoxy-l,2 3,4-di-0-isopropylidene-7-nitro-o-D-gflIocfo-oct-6-enose (135) gave a complex mixture from which there were isolated the trans isomer 136 and the cis and trans isomers of 6,8-dideoxy-l,2 3,4-di-0-isopropylidene-a-D-gaZacto-oct-5-enos-7-ulose (137 and 138). Insofar as the formation of the two ketones involves the loss of... 

Alcohols should, therefore, be avoided as solvents for the recrystallization of nitro-olefinic sugars. The high reactivity of 141 may, perhaps, be ascribed to an inductive effect of the acetal grouping at C-l it is known that 3,3,3-trichloro-l-nitropropene adds alcohols without the aid of a catalyst [I. Thompson, S. Lou-loudes, R. Fulmer, F. Evans, and H. Burkett, ]. Amer. Chem. Soc., 75, 5006 (1953)]. 

In view of the great facility with which base-catalyzed alkoxylations of nitro-olefinic sugars tend to occur, it might be suspected that side reactions involving the formation of methylated derivatives might accompany nitromethane cyclizations of sugar dialdehydes in methanolic medium. There is as yet no evidence for this, but special... 

Oxyamination of olefinic sugars using the Sharpless reaction (TSNHCI-OSO4) has been widely studied as a route to amino-sugars. Compounds of the general... 

Asymmetric induction can be also accomplished through the use of a chirally modified nitro olefin. Sugar-based nitroalkenes participate in thermal [4 + 2] cycloaddition to form enantiomerically pure nitronates [55,97]. Alternatively, diastereoselective cycloadditions are possible with chiral nitroalkenes as illustrated on Scheme 16.15 [47]. The tandem double intramolecular cycloaddition of enantiopure nitro-alkene 62 containing a single stereogenic center provides nitroso acetal 63 with high diastereoselectivity (relative to the existing center) in moderate yield. The product is isolated as a mixture of isomers that is formed due to epimerization of the intermediate nitronate (not shown) and used toward total synthesis of daphnilactone B. 

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