Oxiranic ring rearrangement reactions

Diepoxy-p-menthane, 6, rearranges when heated with alumina in toluene 73). What is the product of this reaction An organic chemist would predict that acid treatment of the diepoxide 6 (Figs. 3 and 32) would induce one or other of the oxirane rings to open. But which of the two will be the more reactive, and would overall reaction necessarily involve such an initial step Furthermore, for each oxirane there are two possible C—O cleavages. 

The thermal ring closure reaction of a 1,3,5-triene to a 1,3-cyclohexadiene occurs by a concerted disrotatory electrocyclic mechanism. An example of the latter is the oxepin-benzene oxide equilibrium (7) which favors the oxepin tautomer at higher temperatures (Section 5.17.1.2). Oxepin (7) was found to rearrange to phenol during attempted distillation at normal pressure (67AG(E)385>. This aromatization reaction may be considered as a spontaneous rearrangement of the oxirane ring to the dienone isomer followed by enolization (equation 7). 

The BF3-promoted rearrangement of several 4,5-epoxy-9-trimethylsilyldecalines having different relative stereochemistry and substitution at the oxirane ring is described. The presence of the silicon at C(9) favours two different main reaction pathways... 

Furthermore, in respect to the regioselectivity of the ring opening reaction of oxiranes, electronic as well as steric factors can play a role. These general considerations stimulate the use of zeolites and non zeolitic molecular sieves as heterogeneous catalysts for such rearrangement reactions in the liquid or in the gas phase in a slurry reactor and in a continuous fixed bed reactor, respectively. 

Strained -oxidoalkyl i enyl selenoxides, such as l-oxido-l-(r-phenylsdenoxyalkyl)cyclopropanes, derived from oxaspiropentanes with tetraalkyl-substituted oxirane rings, and l-(r-hydroxyalkyl)-l-selenoxycyclobutanes, - obtained on oxidation of the corresponding selenides or on reaction of a-li-thioalkyl selenoxides with cyclobutenones, possess a high propensity to rearrange to cyclobutanones... 

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