Stannyl esters

Stannyl esters have been prepared to protect a —COOH group in the presence of an —NH2 group [(n-Bu3Sn)20 or -Bu3SnOH, reflux, 88%]. Stannyl esters... 

Stannyl esters have been prepared to protect a -COOH group in the presence of an -NH2 group [( -Bu3Sn)20 or -Bu3SnOH, CgH, reflux, 88%]. Stannyl esters of A -acylamino acids are stable to reaction with anhydrous amines and to water and alcohols aqueous amines convert them to ammonium salts. Stannyl esters of amino acids are cleaved in quantitative yield by water or alcohols (PhSK, DMF, 25°, 15 min, 63% yield or HOAc, EtOH, 25°, 30 min, 77% yield). ... 

It is believed that this reaction involves the formation of the a-stannyl ester. Metals such as lithium that form ionic enolates would be more likely to reverse the addition step. 

In a,jS-unsaturated stannyl esters the acyl moiety is displaced by mercury(II) salts without affecting carbon-carbon double bonds, as shown in reaction 71322. 

Hata, T. and Sekine, M., Silyl- and stannyl-esters of phosphorus oxyacids — intermediates for the synthesis of phosphate derivatives of biological interest, in Phosphorus Chemistry Directed Toward Biology, Stec, W.J., Ed., Pergamon, New York, 1980, p. 197. 

Beim Erhitzen stochiometrischer Mengen Phosphinsaure-anhydrid und Stannoxan bzw. Diorganozinnoxid auf 100—150° in z.B. Toluol werden exotherm Phosphinsaure-stannyl-ester in guten Ausbeuten gebildet342 z.B. ... 

Transmetallation between stannyl esters and SnCl2 affords tin(ll) enolate equivalents. The reaction of cr-stannyl esters with a-alkoxy or hydroxyl ketones in the presence of SnCl2 gives aldol-type products with high selectivities in a chlelation-controlled manner (Equation (88)).245... 

The reaction of a-stannyl esters with a,/3-unsaturated ketones in the presence of SnCl2 and chlorosilanes gives 1,2-and 1,4-addition products, respectively (Equation (89)).246... 

A stannyl anion reacts with an unsaturated ester to give /3-stannylated esters. In this reaction, the intermediate is a silyl enolate. When a ketoester is employed, an intramolecular cyclization takes place (Equation (117)).289... 

This vanadium method enables the cross-coupling only in combinations of silyl enol ethers having a large difference in reactivity toward radicals and in their reducing ability. To accomplish the crosscoupling reaction of two carbonyl compounds, we tried the reaction of silyl enol ethers and a-stannyl esters based on the following consideration. a-Stannyl esters (keto form) are known to be in equilibrium with the enol form such as stannyl enol ethers, but the equilibrium is mostly shifted toward the keto form. When a mixture of an a-stannyl ester such as 45 and a silyl enol ether is oxidized, it is very likely that the stannyl enol ether will be oxidized preferentially to the silyl enol ether. The cation radical of 45 apparently cleaves immediately giving an a-keto radical, which reacts with the silyl enol ether selectively because of the low concentration of the stannyl enol... 

Reactions of a-stannyl esters and amides 45 with various olefinic compounds were carried out and the results are collected in Table 8. 

Table 8. Reactions of a-Stannyl Ester Derivatives (45) with Various...

Iodoacetoxy(tri-/i-butyl)tin. ICH2COOSnBu3 (1). The reagent is prepared by reaction of iodoacetic acid with bis(tri-n-butyl)tin oxide. The stannyl ester CH3CHICOOSnBu3 (2) is prepared in the same way. 

Triethylstannyl and tributylstannyl esters are prepared for temporary protection of the carboxy function of amino acids.P P l Stannyl esters of N-protected amino acids are stable to anhydrous amines as well as to water and alcohols. Aqueous amines convert them into the ammonium salts. Stannyl esters of N-unprotected amino acids are cleaved in quantitative... 

Several functionalized trialkyltin hydrides have been prepared and used in organic synthesis. For example, an optically active organotin hydride with binaphthyl as chiral center underwent hydrostannylation with methyl methacrylate leading to a -stannyl ester diastereoselectivity, however, was not sufficient [234]. Although a bowl-shaped organotin hydride with bulky aromatic substituents was prepared, the structurally novel tin hydride resulted in quite high chemoselectivity. When tris(2,6-diphenylbenzyl)tin hydride (TDTH) was used for competitive reduction of carbonyls under the influence of a Lewis acid it was observed that unsaturated carbonyl compounds such as benzaldehyde and a,/ -enones are highly resistant to TDTH reduction (Scheme 12.131) [235]. 

Useful alternative preparations of stannanes include palladium-catalysed decarboxylation of stannyl esters. ° Trialkylstannyl and trialkylsilyl anions are highly reactive and will displace halogen without the use of a catalyst. It is possible to directly silylate indoles and pyrroles via electrophilic substitution. ... 

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