1.2- Diols, conversion into oxiranes

Industrial interest has been shown in the generation of oxirans from vicinal hydroxy-acetates (by elimination of acetic acid at temperatures of around 400 or from vicinal diols (through conversion into hydroxy-esters in situ... 

The deracemization of rac-1-methyl-1,2-epoxycyclohexane (64) (Fig. 18.23) has been demonstrated by cells of Corynebacterium sp C12 and Methylobac-terium sp. (Archer et al., 1996 Ueberbacher et al., 2005). A one pot combination of Corynebacterium C12 epoxide hydrolase and acid catalysed ring opening converted rac-1-methyl-1,2-epoxycyclohexane to (1-S, 2-5)-1-methyl-cyclohexane-1,2-diol. Alternatively, instead of the chemical conversion of the unreacted oxirane, the formed diol can be converted into the remaining epoxide (Monfort et al., 2004). 

Carbon-Oxygen Bond Formation. CAN is an efficient reagent for the conversion of epoxides into /3-nitrato alcohols. 1,2-cA-Diols can be prepared from alkenes by reaction with CAN/I2 followed by hydrolysis with KOH. Of particular interest is the high-yield synthesis of various a-hydroxy ketones and a-amino ketones from oxiranes and aziridines, respectively. The reactions are operated under mild conditions with the use of NBS and a catalytic amount of CAN as the reagents (eq 25). In another case, N-(silylmethyl)amides can be converted to A-(methoxymethyl)amides by CAN in methanol (eq 26). This chemistry has found application in the removal of electroauxiliaries from peptide substrates. Other CAN-mediated C-0 bondforming reactions include the oxidative rearrangement of aryl cyclobutanes and oxetanes, the conversion of allylic and tertiary benzylic alcohols into their corresponding ethers, and the alkoxylation of cephem sulfoxides at the position a to the ester moiety. 

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... 

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