DIOLS, VICINAL, EPOXIDES FROM

Diols, meso-, enzymic oxidation to y-lactones, 63, 14 DIOLS, VICINAL, EPOXIDES FROM, 63, 140 m-D1oxane, 2-(2-bromoethyD- [33884-43-4], 62, 148... 

The activities of both haloalkanol dehalogenase (halohydrin hydrogen lyase) that catalyzes the formation of epoxides from alkanes with vicinal hydroxyl and halogen groups, and epoxide hydrolase that brings about hydrolysis of epoxyalkanes to diols are involved in a number of degradations that involve their sequential operation. 

OPTICALLY ACTIVE EPOXIDES FROM VICINAL DIOLS VIA VICINAL ACETOXY BROMIDES THE ENANTIOMERIC METHYLOXIRANES... 

Fatty acid diols can be formed via enzymic or non-enzymic hydrolysis of epoxy compounds (see above). In addition, vicinal diols may originate from the isomerization of hydroperoxy fatty acids, which may proceed without the intermediate formation of epoxides [59]. An acetone powder of the red alga Gracilariopsis... 

Oxirans. - The synthesis of l,2-anhydro-3,4-di-0-benzyl-6-deoxy-a-D-glucopyranose and its conformational analysis have been reported. A range of epoxides have been prepared by base treatment of bromohydrins, which were made by reaction of hydrogen bromide with aldonolactones. A one-pot conversion of vicinal diols into epoxides employs halohydrin ester intermediates generated from cyclic orthoacetates and either acetyl bromide or trimethylsilyl chloride. Levoglucosenone has been transformed into l,6 3,4-dianhydro-p-D-talopyranose by way of a trn/w-iodo-acetoxylation of the alkene moiety... 

Alkylation Reactions. DMF dialkyl acetals undergo a variety of reactions with 1,2-diols. For example, the reaction of trans-cyclohexane-l,2-diol with DMF dimethyl acetal leads to the formation of cyclohexane epoxide (eq 2) with inversion of configuration. Similarly, wej 0-l,2-diphenyl-l,2-ethanediol gives trans-stilbene epoxide stereospecifically (eq 3). This method has also been applied in the synthesis of cholestane epoxide from vicinal diols. If the intermediate 2-dimethylamino-1,3-dioxolane is treated with Acetic Anhydride, reductive elimination to the alkene occurs with retention of stereochemistry (eq 4). " ... 

Enantiopure epoxides and vicinal diols are important versatile chiral building blocks for pharmaceuticals (Hanson, 1991). Their preparation has much in common and they may also be converted into one another. These chirons may be obtained both by asymmetric synthesis and resolution of racemic mixtures. When planning a synthetic strategy both enzymic and non-enzymic methods have to be taken into account. In recent years there has been considerable advance in non-enzymic methods as mentioned in part 2.1.1. Formation of epoxides and vicinal diols from aromatics is important for the break down of benzene compounds in nature (See part 2.6.5). 

Epoxide rings are cleaved by treatment with acid just as other ethers are. The major difference is that epoxides react under much milder condition-because of ring strain. Dilute aqueous acid at room temperature is sufficiem to cause the hydrolysis of epoxides to 1,2-diols, also called vicina/glycols.(Th word vicinal means adjacent," and a glycol is a diol.) More than 3 millK tons of ethylene glycol, most of it used for automobile antifreeze, are produci each year in the United States by acid-catalyzed hydration of ethylene oxid Note that the name ethylene glycol refers to the glycol derived from ethylen just as ethylene oxide refers to the epoxide derived from ethylene. 

Epoxides can also be prepared from a variety of 3-functionalized alcohols such as p-hydroxy sulfoxides," p-hydroxysulfonium salts," P-hydroxy selenides" and vicinal diols. In the use of unsymmetri-... 

Over the past few years, an impressive array of epoxide hydrolases has been identified from microbial sources. Due to the fact that they can be easily employed as whole-cell preparations or crude cell-free extracts in sufficient amounts by fermentation, they are just being recognized as highly versatile biocatalysts for the preparation of enantiopure epoxides and vicinal diols. The future will certainly bring an increasing number of useful applications of these systems to the asymmetric synthesis of chiral bioactive compounds. As for all enzymes, the enantioselectivity of... 

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