Migration of silicon, from carbon to oxygen

When a solution of lithium enolate 68, prepared by the addition of A(Af-dimethyl-2-trimethylsilylacetamide 67 to a THF solution of LDA, is treated with an equivalent amount of propylene oxide 69, a single product 71 is obtained in 75% yield (equation 25) . This result is rationahzed by assuming an initial addition of 68 at the less substimted side of the epoxide, foUowed by the first observed 1,4-migration of silicon from carbon to oxygen (70 to 71). 

Alkynyl complexes. These complexes, which are readily available by reaction of an alkynyllithium with chromium carbonyl followed by methylation with CH3OSO2F, undergo facile Diels-Alder reactions with dienes to provide a general route to ,p-un-saturated chromium carbene complexes. The latter undergo benzannelation or cyclo-hexadienone annelation on reaction with an alkyne. A (trimethylsilyl)ethynyl complex is useful because benzannelation results in migration of silicon from carbon to oxygen to provide a protected phenol. 

A useful type 1 example is the Brook rearrangementa stereospecific intramolecular migration of silicon from carbon to oxygen that occurs for... 

Other processes established include the migration of halogen from silicon to metal (e.g., entries 1,9, and 12) and of fluorine from carbon to metal (entry 4). Ions containing silicon and oxygen are sometimes found (e.g., entries 2 and 16) while they may arise from adventitious hydrolysis, it seems probable that they are also the result of migration of silicon from metal to carbonyl oxygen (see Section III,F,2). 

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