Epoxide ring migration

Entry 8 involves a migration initiated by epoxide ring opening. This reaction involves migration of a vinyl substituent. Entry 9 is a stereospecific migration of the aryl group. The DiBAlH both promotes the rearrangement and reduces the product aldehyde. 

Direct and regioselective transformation of oxaspirohexanes into cyclopentanones is best achieved with lithium iodide.69 Mechanistically, this isomerization occurs via initial opening of the epoxide ring by nucleophilic addition of lithium iodide and is followed by regioselective migration of the more substituted carbon atom of the cyclobutane ring.69-73... 

J. G. Buchanan, Migration of epoxide rings and stereoselective ring opening of acetoxyepoxides, Methods Carbohydr. Chem., 6 (1972) 135-141. 

The enol ether double bond is epoxidized by the peracid. Relief of the epoxide ring strain drives the rearrangement with migration of the silyl group to give the silylated a-hydroxy ketone product. 

Halazy and Krief showed that substituents on the epoxide ring are tolerated, and analogous migration selectivity was exhibited by substrates having one substituent on the cyclobutane and one on the epoxide (equation 127). Substrates with more than two substituents at the pertinent positions have apparently not been examined. 

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