Azido-1,2-diols

Epoxide openings performed with azidotrimethylsilane and di-ethylaluminium fluoride in dichloromethane afforded 3-azido-1,2-diols with good stereo- and regio-selectivities (C2 N2 C2-N2 83 17... 

Interestingly, treatment of 5 with diisopropoxytitanium diazide furnishes 19 and 20 as a nearly 4 1 mixture of regioisomers which are readily separated by silica gel chromatography. The major component of the mixture is azido diol 19 derived from C-3 attack. 

The azido group is again introduced by a titanium mediated reaction. The regioselective ring opening of 10 with diisopropoxy-titaniumdiazide in benzene at 72 °C affords the azido diols 34 and 35 as an inseparable 3 1 mixture. 

However, the catalytic reduction of the azido functionalities in the presence of B0C20 yields the corresponding BOC-protected hydroxy amine which is easily separated by silica gel chromatography. The variation of the conditions did not improve the mixture ratio of the azido diols. However, 11 could be isolated in 60 % yield in that two step sequence. 

Ring opening of 3-cyclohexyl-2,3-epoxypropan-l-ol (39) with sodium azide over H-X gave an 85% yield of the isomeric azido diols, 40 and 41, with the vicinol diol, 40, the almost exclusive product. With other zeolites and clays, the yields were lower but the regioselectivity still favored the formation of 40 (Eqn. 22.39). 6... 

A l-0-silyl-2,5-cyclohexylidene derivative has been transformed into condur-itol E and 2-deoxy-a//o-inositol in which chirality was introduced using a Sharpless asymmetric epoxidation reaction, and 1,4- and 1,3-cyclohexadienes have been bis-epoxidized and the epoxide rings cleaved with azide to afford di-azido diol compounds which were asymmetrized enzymatically. ... 

The DKR of functionalized alcohols such as diols, hydroxy esters, hydroxy aldehydes, azido alcohols and hydroxy nitriles was also taken up as the synthetic uhlity of the products is very high besides such a study will bring out the effect of multifunctional substrates under these reaction conditions to broaden the scope of DKR. Initially, the DKR of diols was achieved with diruthenium catalyst 1... 

If , if , 4 )- (lf , 3S, 4 )-4-Acetoxy-3-3-hydroxy-2-oxocyclochexyl acetate (1,2,4)-4-Acetyl-1 -methylcyclohexane-1,2-diol 3-Azido-2-hydroxy-l-phenylpropan-l-one -t3-Azido-2-hydroxy-l-phenylpropan-2-one... 

Cleavage of 2 -epoxy alcohols.3 The combination of (QHs AlF (1 equiv.) and N3Si(CH3)3 cleaves these epoxides regio- and stereoselectively to provide anti-3-azido-l,2-diols. 

In general, the method of enzymatic cyanohydrin synthesis promises to be of considerable value in asymmetric synthesis because of the synthetic potential offered by the rich chemistry of enantiomerically pure cyanohydrins, including their stereoselective conversion into other classes of compounds such as a-hydroxy carboxylic acids or respective esters, w c-diols, / -aminoalcohols, aziridins, a-azido(amino/fluoro)nitriles, and acyloins [501, 516]. 

Advantageous use of homochiral cyclohexadiene-cis-l,2-diol, available by means of biocatalytic oxidation of chlorobenzene with toluene dioxygenase, has enabled the synthesis of all four enantiomerically pure C18-sphingosines (Nugent, 1998), which are known inhibitors of protein kinase C and important in cellular response mediation for tumor promoters and growth factors. The four requisite diastere-omers of azido alcohol precursors were accessed by regioselective opening of epoxides with either azide or halide ions. 

However, regiopure azido 1,2-diol 19 is converted to the corresponding azido carboxylic acid 22 by oxidative glycol cleavage with periodic acid in the presence of catalytic amounts of ruthenium trichloride. Interestingly, the use of sodium periodate instead of periodic acid resulted in a 10-15 % epimerization of the C-5 stereocenter. 

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