Silanes, homoallylic intermolecular acylation

Three types of products have been observed in intermolecular acylations of homoallylic silanes, the major one being cyclopropylmethyl ketones, along with minor amounts of 3-butenyl ketones and -chlo-ro ketones. It is likely that all derive from the carbenium ion formed by acylation of the double bond, which then undergoes cyclodesilylation or hydride transfer followed by 3-elimination (Scheme 14). The former leads to the cyclopropane, which can ring open to give the chloro products. The latter pathway gives the butenyl ketone, and is supported by location of substituent positions on methylated substrates. However, the direct acylation of the carbon-silicon bond should not necessarily be excluded in consideration of more general cases. Titanium tetrachloride seems the preferred catalyst in these cyclodesilyl-ations, and low temperatures minimize the formation of the chloro by-products. Intramolecular versions... 

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