Organostannanes

Organostannanes are readily synthesized from the corresponding Grignard reagents and tributyltin chloride  

Ligand exchange reactions are an important reaction pathway for organostannanes, for example  

Coordination of Cl to the Sn in SnR4 results in an anionic five-coordinate Sn center, from which an R group can migrate. We thus end up with SnRClg and SnRgCl  

A similar process then leads to the final product, SnR2Cl2  

On account of the electronegativity difference between carbon and tin (Pauling electronegativities C 2.55, Sn 1.96), organostannanes add to carbonyl compounds, particularly 

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Aryl halides react with a wide variety of aryl-, alkenyl- and alkylstan-nanes[548-550]. Coupling of an aryl tritlate with an arylstannane is a good preparative method for diaryls such as 688. The coupling of alkenylstannanes with alkenyl halides proceeds stereospecifically to give conjugated dienes 689. The allylstannane 690 is used for allylation[397,546,551-553]. Aryl and enol triflates react with organostannanes smoothly in the presence of LiCl[554]. 

Arenediazonium salts are also used for the couplina[563], (Z)-Stilbene was obtained unexpectedly by the reaction of the ti-stannylstyrene 694 by addition-elimination. This is a good preparative method for cu-stilbene[564]. The rather inactive aryl chloride 695 can be used for coupling with organostannanes by the coordination of Cr(CO)3 on aromatic rings[3.565]. 

The intramolecular coupling of organostannanes is applied to macrolide synthesis. In the zearalenone synthesis, no cyclization was observed between arylstannane and alkenyl iodide. However, intramolecular coupling take.s place between the alkenylstannane and aryl iodide in 706. A similar cyclization is possible by the reaction of the alkenylstannane 707 with enol triflate[579]. The coupling was applied to the preparation of the bicyclic 1,3-diene system 708[580]. 

The intramolecular insertion of an internal alkyne into an aryl or alkenyl halide 727 generates aryl- or alkenylpalladium as an intermediate, which is trapped with an organozinc or organostannane to give 728. Overall cis addition to the alkyne takes place[595,596]. The reaction of the alkenylstannane 730 with the 2-bromomethylfuran 729 is used for the introduction of a prenyl group[597]. 

The late Professor J. K. Stille pioneered the development of a very effective and versatile palladium-mediated C-C bond forming method - the palladium-catalyzed cross-coupling of organic electrophiles with organostannanes.48 This process continues to enjoy much success in organic synthesis because it proceeds in high yields under mild reaction conditions and because it tolerates a... 

Concentration of perchloric acid, 2 vol. of which were added to 50 vol. of ethanol containing the organostannane. 

The Stille reaction has developed as a popular protocol for the formation of C-C bonds due to the air- and moisture-stability as well as functional group compatibility of organotin compounds. Together with the Suzuki-Miyaura coupling it is one of the most powerful methods for the synthesis of molecules containing unsymmetrical biaryl moieties. However, despite its efficiency, this versatile reaction has slowly been displaced by other procedures that avoid the use of highly toxic organostannanes. 

Procedures for the synthesis of ketones based on coupling of organostannanes with acyl halides have also been developed.211 The catalytic cycle is similar to that involved in coupling with aryl halides. The scope of compounds to which the reaction is applicable includes tetra-u-butylstannane. This example indicates that the reductive elimination step competes successfully with (3-elimination. 

Coupling of organostannanes with halides in a carbon monoxide atmosphere leads to ketones by incorporation of a carbonylation step.249 The catalytic cycle is similar to that involved in the coupling of alkyl or aryl halides. These reactions involve Reactions involving a migration of one of the organic substituents to the carbonyl carbon, followed by... 

Recently Carraher, Naoshima and coworkers effected the modification of polysaccharides employing organostannanes and bis(cyclopenta-dienyl)titanium dichloride, BCTD (20-25). Here we report the modification of dextran employing the interfacial condensation technique using various phase transfer agents utilizing BCTD and dibutyltin dichloride, DBTD. 

These results combined with the total suppression of copolymerization in the presence of hydroquinone as inhibitor indicate that hydrostannylation takes place upon the polyaddition of diorganostannane to the epoxyolefine by a radical mechanism accompanied by hydrogen atom migration in each chain propagation, No addition of organostannanes to the oxirane ring was observed 98>. 

The investigation of the mechanism of organoepoxypolystannane formation shows that radical hydrostannylation of epoxides proceeds mainly during the addition of organostannanes to the C=C bond according to the Former rule, the oxirane ring remaining unaffected 100>102). 

Two additional syntheses of 12 employed organostannane and organobo-rane chemistry. Marshall s synthesis of 12 was based on chiral organostannane A as shown in Scheme 20 [30], while Oehlschlager s one was based on chiral organoborane A (Scheme 21) [31]. 

Coleman established the hydroxypropyl stereochemistry via addition of a homochiral a-alkoxyalkyl organometallic species. This reagent was prepared in high enantiomeric excess using a Noroyi BINAL-H reduction of organostannane 33, which was transmetallated with ra-BuLi to achieve the desired organolithium reagent 35 (Scheme 7.5). Both enantiomers of 35 could be obtained via this route. 

The long reaction times under the action of classic heating were reduced to only a few minutes with single-mode heating at a power of 50-70 W. One example of the use of CH2CH2C6F13 (denoted F-13) -tagged organostannanes is presented in Eq. (11.30) [46],... 

The reaction of silicon organophosphorus betaines with bis(trimethyl-stannyl)methylamine occurs similarly.84,96 Amidobetaine 65, which is most likely formed as an intermediate, decomposes to form silaneimine 66, which is trapped immediately by bis(trimethylstannyl)methylamine. When a twofold excess of organostannane was used, the yield of compound 67 was 90% (Scheme 29). 

FIGURE 4. Configurational stability of chiral organostannanes according to H NMR analysis of diastereotopic methyl signals... 

The main method for the preparation of different types of organostannanes is the ancient Wilrtz reaction between triorganotin halides or diorganotindihalides. Reactions proceed with or without solvent. Usual solvents are benzene, toluene, xylene, diethyl ether and ethanol. Occasionally hquid ammonia is also used. The preferred metals for this reaction are sodium and lithium. In the case of triorganotin halides, the reaction leads to symmetric hexaorganoditin compounds72 ... 

Unsymmetric organostannanes can be prepared by the reaction of triorganotin sodium compounds in hquid ammonia with a triorganotin halide73,74 ... 

Another important route to obtain organostannanes is the hydrogenolytic cleavage of tin-nitrogen bonds96,97. This reaction obeys the general scheme... 

Acetylenic compounds and acetylenic organotin compounds are widely used in the synthesis of many organostannane derivatives of importance in further synthetic procedures. 

Hannon and Traylor158 used a specifically labelled organotin hydride, l/iiw-3-deutero-2-trimethylstannylbutane, to determine the mechanism and stereochemistry of the hydride abstraction from an organostannane by a carbocation (equation 101). 

The application of organostannanes in rhodium-catalyzed 1,4-addition reactions was first studied by Oi and co-workers.137,137a The treatment of enones or enolates with a slight excess of aryltrimethylstannane and catalytic amounts of [Rh(COD)(MeCN)2]BF4 generates the conjugate addition products in good yields. The use of protic additives enhanced the yield of the reaction (Scheme 48).138... 

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