Stannyl formates, decarboxylation

The formation of a hexaalkyldistannane by heating together the hexaalkyl-distannoxane and formic acid (equation 18-20, R = Bu, Bu1, Oct) similarly involves the reduction of SnX by SnH.20 The stannyl formate is formed, and decarboxylates to give the tin hydride, which then reduces the distannoxane. Residual formate can be extracted into methanol, in which the distannanes (ca. 65-70% yields) are insoluble. 

Stannyl- (and -silyl-) carboxylic acids undergo oxidative decarboxylation with LTA under mild conditions to provide the corresponding alkenes. This represents an improvement on the well-known alkene-forming decarboxylation of acids with LTA, which requires thermtd or photochemical conditions, for example. The directing metal effect leads to improved yields and regioselectivity. However, stereo-specific alkene formation did not occur and this could imply free radical involvement or transmetallation (Pb for Sn) (stereochemistry ) followed by cation formation, see for example Scheme 27. 

Diketene similarly reacts readily with tributyltin oxide in THF at room temperature47 to give the stannyl 3-stannyloxybut-3-enoate which rearranges to the 2-enolate this enolate will then give an ene reaction with an aldehyde,48 or react with an alkyl halide,49 followed by decarboxylation, providing a route to ketones, enones, and ketoaldehydes. Similar reactions with bromomethyl P- or y-lactones result in the formation of P-hydroxy-y-lactones or y-hydroxy-5-lactones. 

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