Ketene stannyl acetal

Penta-coordinated stannates undergo the Michael reaction with enones and nitroalkenes or cyanoalkenes due to the high nucleophilicity (Schemes 3-201, 3-202, and 3-203). This strategy is applicable to ketene stannyl acetals, which are less reactive than ketene silyl acetals due possibly to the easy equilibrium between 0-Sn and C-Sn tautomers, the C-Sn tautomers being predominating at temperatures above 0 Normally, Qf-stannyl esters are much less reactive with electrophiles. However,... 

Kiigelrohr apparatus. Flash column chromatography (hexane) of the residue afforded ketene stannyl(telluro) acetals as yellow liquids. 

General procedure for the synthesis of a-bromovinyl tellurides from ketene stannyl (telluro) acetals To a solution of the appropriate ketene stannyl(telluro) acetal (1.0 mmol) in CH2CI2 (10 mL) cooled at -78°C (at 0°C for 5 h) was added dropwise a solution of NBS (0.445 g, 2.5 mmol) in CH2CI2 (25 mL). Th reaction mixture was stirred for 6 and 12 h (R=H). It was transferred to an Erlenmeyer flask and treated with a solution... 

The low oxidation potentials of stannyl compounds gave us a clue to develop the selective cross-coupling reaction between the a-posi-tions of two carbonyl compounds. Generally, silyl enol ethers or ketene silyl acetals are employed for this purpose to prepare 1,4-di-... 

Cyclopropanated allylboration reagents have been used to homoallylate and homocrotylate aldehydes. A zinc-mediated a-prenylation of aldehydes and ketones has been reported conventional conditions have yielded mainly the y-adduct to date. " A racemic allene has been hydroborated in an enantioconvergent manner the enantioenriched crotylborane then reacts with aldehydes in high ee to give ( j-stannyl-homoallylic alcohols. A copper-catalysed y-selective and stereospecific allylic alkylation of ketene silyl acetals has been reported. ... 

Arylacetate esters have been generated by coupling aryl bromides with stannyl enolates generated from silyl ketene acetals. 

Telluro(seleno)ketene acetals, 1-seleno-2-telluro-ethenes, telluro ketene acetals, telluro(stannyl)ketene acetals and telluro(thio) ketene acetals... 

Following the precedent methodologies, telluro(stannyl) ketene acetals are achieved by the hydrozirconation of stannyl acetylenes and successive reactions with butyl tellurenyl... 

Protic-acid-catalyzed Michael additions (59) are subject to most of the limitations of base-catalyzed Michael additions (regioselectivity and stereoselectivity of enol generation, polyaddition, etc.), and hence, the stereochemistry has been little studied (60). At low temperatures silyl and stannyl enol ethers,+ ketene acetals, and allyl species are unreactive to all but the most reactive activated olefins. However, it was discovered by Mukaiyama and co-workers that enol ethers and ketene acetals react with a,/f-unsaturated carbonyl compounds in the presence of certain Lewis acids (4,61,62). Sakurai, Hosomi, and co-workers found that allylsilanes behave similarly (5,63,64). 

With the substrate (83), the 0-stannyl ketene acetal (84) can be made by 1,4-hydrostannation. Normally, addition of tin hydride to alkenic esters gives the C-stannylated compounds. An example is the reaction of (85) with tri-n-butyltin hydride. ... 

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