Stannyl anions ethers

This method was applied to the diastereoselective synthesis of vinyl ethers from readily available a-alkoxy aldehydes9. Reasonable selectivity in favor of the syn-adduct is observed when the stannyl anion is modified by softer metal salts such as zinc halides or copper(I) bromide. 

In the presence of a nucleophile like a bromide ion, stannyl enol ethers are converted into anionic pentacoordinate stannates, which nucleophilically react with organic halides to give or-alkylated carbonyl compounds. In contrast, such penta-coordinated tin species hardly react with carbonyl electrophiles. The higher coordinated species is also generated by treatment of tin(IV) enol ethers with not only Bu4NBr but an aprotic polar solvent like Such pentacoordinate stannates add in a similar... 

SET photochemistry is involved in the reaction between the enones (371) and the a-stannyl ethers (372) in methanol. The products are the 3-sub-stituted cycloalkanes (373) which arise from addition of aryloxymethyl radicals to the enones. Irradiation (X > 400 nm) of the stannanes (374) in the presence of the ketones and aldehydes (375) affords two products identified as (376) and (377). The former of these is dominant and the reaction arises by an electron transfer from the stannane to the ketone. The resultant stannane radical-cation undergoes fission to yield an alkoxy allyl radical and the tin cation. The alkoxyalkyl radical adds to the carbonyl radical-anion with a preference for... 

Enol stannyl ethers have recently been used as synthetic equivalents of enolate anions. However, or-ganotin enol ethers usually exist as mixtures of C- and (7-metallated species, irrespective of the methods of preparation. Nevertheless, the two tautomers (71) and (72) often show similar reactivity and can be considered collectively as tin enolates . 

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