Stannyl anions reactions with

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... 

Stannyllithium compounds are important as sources of nucleophilic stannyl anions, and the dialkyltin lithium hydrides, R2SnLiH, have recently come to prominence as their reaction with electrophilic alkyl halides gives hydrides, R1R2SnH, with mixed alkyl groups (see Section 3.14.18.1).397... 

Bulky stannyl anions which are not available from stannyl hydrides (see Section I.A.l) were prepared by using the reaction of alkali metals with tin halides (equations 24 - 26)31,40 41. 

Cleavage with cesium fluoride was used in the case of stannylsilanes (equation 34)49. The generated stannyl anions are very effective in synthetic applications, mainly in abstraction of halogen to initiate organic 4 + 2 cycloadditions (equation 35)49, a reaction which constitutes one of its chemical characterizations. 

Another application of the direct alkylation of metal-14 anions is the synthesis of polymer-supported organotin hydrides. These were prepared by the reaction of stannyl group was separated from the phenyl ring of polystyrene by two, three or even four carbon spacers. These polymers were found to contain 0.8-1.4 mmol of Sn-H per gram. The reducing ability of the polymer-supported organotin hydrides was monitored by reactions with haloalkanes (Scheme 22)142. 

Stannyllithiums are synthetic equivalent of stannyl anions. The reaction of 2,6-di- 7 /-butyl-4-rncthylphcnyl(UI IT) esters with BuLi, followed by the addition of Bu3SnLi, and trapping of the resulting lithium enolate with phenyldi-methylchlorosilane leads to silyloxyvinylstannanes, which are allowed to the subsequent coupling with vinyl iodides (Equation (110)).279... 

Silyl, germanyl and stannyl alk-l-ynyl ketones have been prepared from 2-lithio-2-(trimethylsilylethynyl)-l,3-dioxolane 448. The deprotonation of the dioxane 447 with n-BuLi at — 65 °C afforded the acyl anion 448 which, after reaction with trimethylsilyl, trimethylgermanyl and trimethylstannyl chloride, gave the expected derivatives (Scheme 117)658. Hydrolysis of these products with 0.01 M sulfuric acid at room temperature in aqueous acetone gave the corresponding acyl derivatives 449. On the other hand, the reaction of the intermediate 448 with alkyl halides allows the synthesis of acetylenic ketones659. 

Several publications about oxidative addition of metal or organometal derivatives to stannylenes describe a new and efficient way to stannyl anions . The reaction of CpLi with Cl2Sn resulted in a mononuclear complex as colorless cubic crystals obtained in 48% yield (equation 53) °. Its structure was resolved by X-ray diffraction and shows a complete separation of the ion-pair . 

Trialkylsilyl higher-order cyanocuprates are prepared directly by trans-metallation of silylstannanes with higher-order dibutylcyanocuprates (Scheme 32) (101). In this method, steric bulkiness around silicion is essential for formation of the silylcuprates, so that the t-butyl or thexyl group is present on silicon otherwise, stannyl anion is formed. These reagents undergo typical silyl-cupration reactions, as mentioned earlier. 

In order to provide a modular route compatible with different lengths of the spacer (>2 carbon units), another route has been developed consisting of initial grafting of a terminal chloroalkyl spacer (on Amberlite XE 305). The addition of an appropriate stannyl anion followed by a halogenation reaction affords the polymer C (Scheme 5.5.4). ° ... 

A delocalized 0-stannyl radical anion can also be generated from the reaction of an a,/ -unsaturated ketone or aldehyde with tributyltin hydride and radical initiator AIBN [3, 4, 5a, 5b]. Thus, a,/ -unsaturated carbonyl compound 4 (R or R = H or alkyl), can be reacted with wBu SnH under standard free-radical conditions to give allylic O-stannyl ketyl species (5 6), shown in Scheme 2. After hydrogen atom transfer to the -position of 6, a synthetically useful tin(IV) enolate is produced [5b, 5d, 5g. Allylic 0-stannyl ketyls have both one- (radical) and two-electron (anionic) sites for reactivity. These reactions can proceed in a sequential manner - a rapidly-evolving methodology in organic synthesis [2, 5, 8j. If the one-electron reactivity in 6 is used with a radicophile, then the tin enolate or two-electron reactivity can be used in reactions with suitable electrophiles (E ). Note that the carbonyl species. 

Methoxy-substituted azomethine anions can also be generated by reaction of a-(tri- -butyl-stannyl)imidate esters, which undergo lithium-tin exchange on reaction with alkyllithium reagents. The adducts eliminate methanol, generating A -pyrrolenines (Equation (58)) <94TL264l>. 

Generation and Reactions of Metal-free Stannyl Anions from M SiSnBua and Highly Dissociated Fluorides. Aryl, vinyl, and allyl anions are easily generated by reactions of the appropriate precursor with Me3SiSnBu3 and a reactive fluoride source. Presumably, the reaction proceeds through a highly dissociated tributylstannyl anion. The examples (eqs 19-22) illustrate the use of various halide sources for the synthesis of these reactive intermediates. 

Photonucleophilic aromatic substitution reactions of phenyl selenide and telluride with haloarenes have also been proven to involve the S jlAr mechanism, with the formation of anion radical intermediates. Another photonucleophihc substitution, cyanomethylation, proves the presence of radical cations in the reaction mechanism. Liu and Weiss have reported that hydroxy and cyano substitution competes with photo substitution of fluorinated anisoles in aqueous solutions, where cation and anion radical intermediates have been shown to be the key factors for the nucleophilic substitution type. Rossi et al. have proposed the S j lAr mechanism for photonucleophihc substitution of carbanions and naphthox-ides to halo anisoles and l-iodonaphthalene. > An anion radical intermediate photonucleophilic substitution mechanism has been shown for the reactions of triphenyl(methyl)stannyl anion with halo arenes in liquid ammonia. Trimethylstannyl anion has been found to be more reactive than triphenylstannyl anion in the photostimulated electron- transfer initiation step. 

In a comparable way as outlined below for lead, Klinkhammer and coworkers obtained a number of oligosilanylated stannyl anions and radicals by reaction of oligosilanyl anions with diamino and diaryloxy stannylenes [246]. Scheschkewitz and coworkers found that the reaction of a disilenyl lithium species with Me2SnCl2 gave a chlorinated disilastanniranes (9) [247]. 

In a similar way as mentioned above for subvalent Ge(I) halides Schnepf and coworkers have also reported several reactions of Sn(I) halides with sUyl anions which gave silylated Zintl-type clusters 809 and Snio [248-251], In addition to these clusters smaller units such as the stannyl anion [ (Me3Si)3Si 3Sn] , the cyclotristannene [ (Me3Si)3Si 4Sn3], and the novel cluster [ (Me3Si)3Si 4 (Me3Si)2SiSii4] formed in the course of fliese reactions [252, 253]. 

The preparative potential of silyl- or stannyl-substituted polynuclear complexes is currently far from being exploited. Due to the reactivity of silyl ligands, selective cleavage of metal-silicon bonds is possible. In some cases this was observed during the reaction of an anionic silyl complex with metal... 

In the first systematic study on nucleophilic substitutions of chiral halides by Group IV metal anions, Jensen and Davis showed that (S )-2-bromobutane is converted to the (R)-2-triphenylmetal product with predominant inversion at the carbon center (Table 5)37. Replacement of the phenyl substituents by alkyl groups was possible through sequential brominolysis and reaction of the derived stannyl bromides with a Grignard reagent (equation 16). Subsequently, Pereyre and coworkers employed the foregoing Grignard sequence to prepare several trialkyl(s-butyl)stannanes (equation 17)38. They also developed an alternative synthesis of more hindered trialkyl derivatives (equation 18). 

Haloarenes have been found to undergo nucleopilic substitution when irradiated with the triphenyl stannyl anion46, reacting via a radical S l mechanism. In many cases the reaction will only occur under photochemical conditions. The reaction is found to proceed with chloro- and bromo-substituted arenes, but not iodo-compounds. The anion is produced either by treatment of triphenyltin chloride or hexaphenylditin with sodium metal in liquid ammonia, and will react with a wide variety of arenes (reaction 30). 

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