Regioselective protection stannyl activated

SCHEME 3.13 Examples of stannyl activated regioselective protection. 

Free radical additions of phenylthio or stannyl radicals to 2-alkenyl 2-siloxycyclo-propanes afford similar products although a completely different mechanism is operative 84). This direct generation of protected y-oxoesters 144 and 145 is of interest since the silyl enol ether function might be usable for regioselective C-C-bond formation and the allyl stannane moiety in 145 could be activated for subsequent transformations. Yet further examples have to demonstrate utility and scope of this mode of ring opening. 

Selective activation of hydroxyl groups by the stannylation procedure is an established practice to efficiently manipulate diols and polyols [53, 54]. Among the various reagents and methods, activation through dialkylstannylene acetals is noteworthy. This two-step protection method involves the conversion of dihydroxy substrates into cyclic dialkyl dioxastan-nanes which, in turn, are treated with suitable nucleophiles, to regioselectively afford the corresponding mono alkyl, silyl or acyl derivatives under neutral conditions. 

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