Alkene oxides hydration

Carbocation intermediates are not involved m hydroboration-oxidation Hydration of double bonds takes place without rearrangement even m alkenes as highly branched as the following... 

Hydroboration-oxidation (Sections 6 11-6 13) This two step sequence achieves hydration of alkenes in a ste reospecific syn manner with a regiose lectivity opposite to Markovnikov s rule An organoborane is formed by electro philic addition of diborane to an alkene Oxidation of the organoborane inter mediate with hydrogen peroxide com pletes the process Rearrangements do not occur... 

Together with glutathione conjugation, hydration is a major pathway in the inactivation and detoxification of arene oxides. Exceptions to this rule will be treated when discussing polycyclic aromatic hydrocarbons. Arene oxides are good substrates for microsomal EH, as evidenced in Table 10.1, where hydration of selected arene oxides, alkene oxides, and cy-cloalkene oxides by purified rat liver epoxide hydrolase is compared. The hy- ... 

As explained in the Introduction, alkene oxides (10.3) are generally chemically quite stable, indicating reduced reactivity compared to arene oxides. Under physiologically relevant conditions, they have little capacity to undergo rearrangement reactions, one exception being the acid-catalyzed 1,2-shift of a proton observed in some olefin epoxides (see Sect. 10.2.1 and Fig. 10.3). Alkene oxides are also resistant to uncatalyzed hydration, thus, in the absence of hydrolases enzymes, many alkene oxides that are formed as metabolites are stable enough to be isolated. 

Hydration means, in general, addition of the elements of water to a substance. Most of these reactions are non-catalytic or homogeneously catalysed processes. In this section, only hydration of olefins to alcohols, of acetylene to acetaldehyde, and of alkene oxides to glycols will be treated, since they are typical reactions where the application of solid catalysts has become important. 

The fatty acid oxidation pathway comprises a sequence of steps frequently encountered in biology (1) oxidation of an alkane to produce an alkene (2) hydration of the alkene to form a hydrojcyl group and (3) oxidation of the hydroxyl group to form a kelo group. This three-step sequence is also found in the Krebs cycle and the isoJeucine catabolic pathway. 

Kapitulnik J, Levin W, Lu AYH, et al. 1977. Hydration of arene and alkene oxides by epoxide hydrase in human liver microsomes. Clin Pharmacol Ther 21 158-165. 

The oxidative hydration of alkenes to aldehydes or ketones is most often achieved on the laboratory scale in two steps by hydroboration followed by oxidation of the intermediate alcohol. 

D. Hydration Epoxide hydratase (EC 4.2.1.64), also called epoxide hydrase or hydrolase Epoxides (arene and alkene oxides) Epoxides are hydrated to dihydrodiols. Product glycols which are stereochemically fixed by a ring structure invariably have the /ra/i5-configuration... 

The result of hydroboration and subsequent oxidation of an alkene is hydration of the carbon-carbon double bond, here illustrated by the hydroboration-oxidation of 1-hexene to give 1-hexanol. 

Organic acids Hydration of fumaric acid, oxidation of alkenes, oxidation of isobutyric acid, reduction of 3-chloroacetic acid ester, aminolysis of histidine Hasegawa (1982)... 

Oxidation of tridecylborane gives 1 decanol The net result is the conversion of an alkene to an alcohol with a regioselectivity opposite to that of acid catalyzed hydration... 

The mechanistic complexity of hydroboration-oxidation stands m contrast to the simplicity with which these reactions are carried out experimentally Both the hydrobo ration and oxidation steps are extremely rapid reactions and are performed at room tern perature with conventional laboratory equipment Ease of operation along with the fact that hydroboration-oxidation leads to syn hydration of alkenes and occurs with a regio selectivity opposite to Markovmkov s rule makes this procedure one of great value to the synthetic chemist... 

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