Cycloalkenes into alcohols

Ozonolysis of cycloalkenes.b Cycloalkenes are converted by ozonation in the presence of an alcohol (usually methanol) into an acyclic product with an aldehyde group and an a-alkoxy hydroperoxide group at the terminal positions. The products are usually difficult to purify, but they can be converted into useful products that retain differentiated terminal functionality. 

Allylic diethylboranes.1 These boranes (2) can be prepared from 1-methyl-cycloalkenes and 2-alkenes by metallation with trimethylsilylmethylpotassium2 followed by reaction with 1. The products react with acetaldehyde to form homoallylic alcohols (3), which can be converted into a,(3- and p,y-unsaturated ketones. 

The reduction of epoxides withborane is noteworthy as it gives rise to the less substituted alcohol as the major product (7.96), in contrast to reduction with complex hydrides (compare with Scheme 7.71). The reaction is catalysed by small amounts of sodium or lithium borohydride and high yields of the alcohol are obtained. With 1-alkylcycloalkene epoxides, the 2-alkylcycloalkanols produced are entirely cis, and this reaction thus complements the hydroboration-oxidation of cycloalkenes described in Section 5.1, which leads to trans products. Reaction with borane in the presence of boron trifluoride has also been used for the reduction of epoxides and for the conversion of lactones and some esters into ethers. 

Cycloalkenes are converted into a,B-unsaturated ketones using Bu "00H in the presence of catalytic amounts of [Cr(C0)g]. Some secondary alcohols have been shown to be inert to these oxidizing... 

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