Glycols cycloalkene

Hundreds of VOCs are found in a typical nonindustrial indoor environment. Many of these compounds are aromatic hydrocarbons, alkenes, alcohols, aliphatic hydrocarbons, aldehydes, ketones, esters, glycols, glycolethers, halocarbons, cycloalkanes and terpenes [2] but amines hke nicotine, pyridine, 2-pi-coline, 3-ethenylpyridine and myosmine are also widespread, especially in smoking microenvironments [3]. Moreover, low molecular weight carboxylic acids, siloxanes, alkenes, cycloalkenes and Freon 11 are frequently encountered in typical nonindustrial indoor air [1]. 

Acid-catalyzed hydrolysis of an epoxide derived from a cycloalkene gives a trans glycol (hydrolysis of... 

In Section 6.5A, we studied oxidation of alkenes by osmium tetroxide in the presence of peroxides. This oxidation results in syn stereoselective hydroxylation of the alkene to form a glycol. In the case of cycloalkenes, the product is a cis glycol. The first step in each oxidation involves formation of a cyclic osmate and is followed immediately by reaction with water to give a glycol. 

At this point, let us compare the stereochemistry of the glycol formed by acid-catalyzed hydrolysis of an epoxide with that formed by oxidation of an alkene with osmium tetroxide (Section 6.5A). Each reaction sequence is stereoselective but gives a different stereoisomer. Acid-catalyzed hydrolysis of cyclopentene oxide gives trans-l,2-cyclopentanediol osmium tetroxide oxidation of cyclopentene gives ds-1, 2-cyclopentanediol. Thus, a cycloalkene can be converted to either a cis glycol or a trans glycol by the proper choice of reagents. 

Acid-Catalyzed Hydrolysis of Epoxides (Section 11.9A) Hydrolysis of an epoxide derived from a cycloalkene gives a trans glycol. The reaction involves initial protonation of the epoxide O atom followed by nucleophilic attack of water and then loss of a proton to give the trans diol.The reaction also occurs with alcohol nucleophiles, and when there is a difference, reaction of the nucleophile occurs predominantly at the more substituted carbon of the protonated epoxide. 

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