Oxiranes oxidative cleavage

The K-region -oxirans (63) and (64), of interest in studies of chemical carcinogenesis, have been prepared by cyclization with TDAP of the dialdehydes obtained by oxidative cleavage of the parent hydrocarbons.54... 

Using the MTO/H2O2 system in terf-butanol, both compounds are degraded to yield vanillin in almost quantitative yield. This oxidative cleavage is proposed to proceed via MTO-catalyzed epoxidation followed by hydrolysis of the oxirane ring and subsequent MTO-catalyzed cleavage of the diol (Scheme 5) [89]. 

This chapter will define an oxidation in general terms. Various reagents will be introduced that oxidize an alcohol to an aldehyde or to a ketone. In some cases, alcohols may be oxidized to a carboxylic acid. Oxidation of alkenes will be revisited—specifically, for the oxidation of an alkene to an oxirane or to a 1,2-diol. Oxidative cleavage with ozone will be revisited, and new methods for oxidative cleavage will be introduced. 

Oxirane on thermolysis or photolysis suffers C—O homolysis to give a plethora of products (Scheme 2). Substituted oxiranes behave similarly on thermolysis although some C—C cleavage is observed (Scheme 3). Cyclopentene and cyclohexene oxides undergo only C—O cleavage (Scheme 4). 

Oxygen donors like peroxy acids, ozone, and pyridine IV-oxides cause carbon-carbon cleavage, perhaps by formation of a perepoxide (43 Scheme 30) (81JCS(P1)1871). Other oxidants have also been reported to react with oxiranes (64HC( 19-1)228). 

---