Tributyltin halides

This material was used to show that tributyltin halides decompose into dibutyltin dihalides and butyltin trihalides in the environment. 

Trimethyltin halides are fairly soluble in water, and can often be washed out of a solution of the reaction mixture in an immiscible solvent. If the desired product is polar, it can be separated from tributyltin halides by partition between acetonitrile and hexanes, which are immiscible.52 53... 

Lithiation of the perhydro-2-methyl-l,3-oxazine (91) takes place at C-4, allowing the selective introduction of various groups at this position. Electrophiles such as alkyl, trimethylsilyl, and tributyltin halides all react with the lithiated oxazine to afford the corresponding derivatives, which can then be ring-opened to substituted 3-aminopropanols (92) (Scheme 21). Aldehydes give rise to the bicyclic oxazolones (93), whereas treatment with carbon dioxide, followed by acidic work-up, yields the 3-aminobutyrolactone (94) <93JOC823>. 

The tributyltin hydride-mediated carbon-carbon bond formation via radical addition and cyclization of alkyl halides with alkenes has often been a choice for construction of various organic molecules [1], However, the requirement for high-temperature initiators or photo initiation and the difficulties associated with purification of the products from tributyltin halides tend to limit the widespread use of these methods, despite the efforts to make the methods easier [Ic, 2], Recently, nickel-mediated radical additions and cyclizations have been introduced as promising alternatives to the tributyltin hydride methods. These are the nickel powder-acetic acid method for cyclization of haloamides to y-lactams, y -lactams and in-dolones, the borohydride exchange resin-nickel boride method for radical addition, nickel-catalyzed electroreductive cyclization and nickel-catalyzed Kharasch addition of polyhalo compounds. 

The hydrogenolyaia of cyclopropane rings (C—C bond cleavage) has been described on p, 105. In syntheses of complex molecules reductive cleavage of alcohols, epoxides, and enol ethers of 5-keto esters are the most important examples, and some selectivity rules will be given. Primary alcohols are converted into tosylates much faster than secondary alcohols. The tosylate group is substituted by hydrogen upon treatment with LiAlH (W. Zorbach, 1961). Epoxides are also easily opened by LiAlH. The hydride ion attacks the less hindered carbon atom of the epoxide (H.B. Henhest, 1956). The reduction of sterically hindered enol ethers of 9-keto esters with lithium in ammonia leads to the a,/S-unsaturated ester and subsequently to the saturated ester in reasonable yields (R.M. Coates, 1970). Tributyltin hydride reduces halides to hydrocarbons stereoselectively in a free-radical chain reaction (L.W. Menapace, 1964) and reacts only slowly with C 0 and C—C double bonds (W.T. Brady, 1970 H.G. Kuivila, 1968). 

Tin enolates of ketones can be generated by the reaction of the enol acetate 733 with tributyltin methoxide[60i] and they react with alkenyl halides via transmetallation to give 734. This reaction offers a useful method for the introduction of an aryl or alkenyl group at the o-carbon of ketones[602]. Tin enolates are also generated by the reaction of siiyl enol ethers with tributyltin fluoride and used for coupling with halides[603]. 

Alkyl halides can be reduced to alkanes by a radical reaction with tributyltin hydride, (C4H9)3SnH, in the presence of light (hv). Propose a radical chain mechanism by which the reaction might occur. The initiation step is the light-induced homolytic cleavage of the Sn— H bond to yield a tributyltin radical. 

Tributyltin hydride, reaction with alkyl halides. 358 Tricarboxylic acid cycle, see Citric acid cycle... 

For reviews of organotin hydrides, see Neumann, W.R Synthesis, 1987,665 Kuivila, H.G. Synthesis, 1970,499, Acc. Chem. Res., 1968,1,299. Tributyltin hydride also reduces vinyl halides in the prescence of a palladium catalyst. See Uenishi, J. Kawahama, R. Shiga, Y Yonemitsu, O. Tsuji, J. Tetrahedron Lett., 1996, 37, 6759. 

The coupling between an aryl halide or triflate and an amine is known as the Buchwald-Hartwig amination [138]. Originally it was described using a tributyltin amine [139,140] and was thus considered to be a coupling reaction. Subsequently, tributyltin amine was replaced by a standard amine and a strong base. It is a reaction of great academic and industrial interest [11]. 

COUPLING OF ALLYLIC HALIDES WITH TRIBUTYLTIN CHLORIDE ... 

Aryl halides can also be reduced by tin hydrides76,77, although these reactions always require initiators because the stronger C—X bonds in aryl halides are less reactive than the C—X bonds in alkyl halides. In fact, a series of meta- and para-substituted bromobenzenes, where X is either meta- or para-CH3O-, C=N, Cl, F, CF3, CH3, Bu-f or 2,6-dichloro, have been reduced by tributyltin deuteride (equation 60). It is worth noting that the more reactive bromide is reduced selectively in the presence of the less reactive chloride and fluoride groups (equation 61). 

Although the tin hydride reductions of alkyl halides seem simple, one must be careful because these reactions occur by a free radical mechanism. This is important, because the carbon radical produced in the reaction can isomerize68,78 and one often obtains two different stereoisomers from the synthesis. Another problem is that chiral centres can be lost in tin hydride reductions when an optically active halide is reduced. One example of this is the reduction of benzyl-6-isocyanopenicillanate with tributyltin deuteride78 (Scheme 14). The amount of isomerization depends on the temperature, the concentration of the tin hydride and the presence of and /-substituents78-82. However, some authors have reported tin hydride reductions where no racemization was observed78. 

Like most aryl halides, furyl halides and furyl triflates have been coupled with a variety of organostannanes including alkenyl, aryl, and heteroaryl stannanes in the presence of catalytic palladium. Carbamoylstannane 66 was prepared by treating lithiated piperidine with carbon monoxide and tributyltin chloride sequentially. The Stille reaction of 66 and 3-bromofuran then gave rise to amide 67 [61]. In another example, lithiation of 4,4-dimethyl-2-oxazoline followed by quenching with MesSnCl resulted in 2-(tributylstannyl)-4,4-dimethyl-2-oxazoline (68) in 70-80% yield [62], Subsequent Stille reaction of 68 with 3-bromofuran afforded 2-(3 -furyl)-4,4-dimethyl-2-oxazoline (69). 

Radical homologation. This tin pinacolate is known to generate trimethyltin radicals at 60° and appears to be superior to tributyltin hydride as a source of stannyl radicals for addition of alkyl halides to O-benzylformaldoxime (equation I).1 Iodides, bromides, and selenides can be used as radical precursors. The same... 

Hexabutyldistannane, which is an important reagent in many organic syntheses, can be prepared very conveniently by reducing bis(tributyltin) oxide with sodium borohydride in ethanol at room temperature. After 5 min, the only tin species present is tributyltin hydride, but in 2 h, its decomposition is catalyzed by the ethoxide ion that is formed to give the distannane in 83% yield.444 Hexaalkyldistannanes, R3SnSnR3 (R = Et, Pr, or Bu), are obtained in ca. 50% yield when the corresponding trialkyltin halides are treated with zinc powder in THF.445... 

The silylated tin compound 199, obtained from tributyltin hydride and N-bis(trimethylsilyl)propargylamine (198) in the presence of a trace of AIBN (2,2/-azobisisobutyronitrile), is a versatile reagent for the preparation of allylic amines. Treatment with aryl bromides ArBr (Ar = Ph, 4-MeOCgH4, 4-O2NC6H4 etc.) under Pd(PPh3)4 catalysis yields the silylated amines 200, which are hydrolysed by acids to the free amines 201. 199 is converted into the lithium compound 202, which is transformed into 203 by aqueous ammonium chloride and into 204 by the action of alkyl halides RX (R = Me, Et or allyl) (equation 76)204. 

These observations do not, however, mean that TBT carboxylates and TBTCl are ionic in nature. After detailed analysis of the physical evidence such as the low specific conductance and dipole moment of trialkyltin halides, Neumann has concluded that they have no "salt-like constitution" (6). Bonding in the trialkyltin carboxylates also is essentially similar to that in covalent alkyl esters, as evidenced by the low dipole moment of 2.2D for tributyltin acetate in benzene, as compared to 1.9D for alkyl acetates (7). 

The same research group has further performed radical carbonylation reactions on the same microreactor system [36]. First, alkyl halides were initiated and effectively reacted with pressurized carbon monoxide to form carbonyl compounds. The principle was subsequently successfully extrapolated to the multicomponent coupling reactions. 1-Iodooctane, carbon monoxide and methyl vinyl ketone were reacted in the presence of 2,2 -azobis(2,4-dimethylvaleronitrile) (V-65) as an initiator and tributyltin hydride or tris(trimethylsilyl)silane (TTMSS) as catalyst (Scheme 15). 

Previously, vinyl radicals for cyclization reactions were produced by the reduction of vinyl halides with tributyltin hydride. In the present... 

The tributyltin radical abstracts a halogen atom from the alkyl halide and the chain is propagated as follows—... 

Radical carbonylation reaction serves as a powerful tool for the synthesis of a range of carbonyl compounds. Radical carbonylation has been successfully applied to the synthesis of functionalized ketones from alkyl, aryl, and alkenyl halides.The radical aminocarbonylation reaction of alkynes and azaenynes provided efficient routes to 2-substituted acrylamides, lactams, and pyrrolidinones. For example, the aminocarbonylation of 4-pentyn-l-yl acetate 318 initiated by tributyltin hydride (Bu"3SnH) (30mol%) with AIBN (20mol%) gave acrylamide 325 in 92% yield (Scheme 43).A proposed mechanism starts from the addition of tributyltin radical 319 to alkyne... 

Dr. Dessy Yes, and it indicates why you had such a difficult time with the kinetics. The solvent system that was used had hydrogen bonding possibilities with the halide ion. Henry Kuivila has decomposed tributyltin hydride in alcohol solvents with carboxylic acids, and there is no effect of halide ion. Apparently the tin under those conditions cannot compete with the solvent for the halide ion. Halide ion is all hydrogen bonded. 

In the presence of proton and/or Lewis acid and strong nucleophiles bicyclo[3.2.0]heptan-6-ones are converted to 3-substituted cycloheptanones (Table 15). Bicyclo[3.2.0]heptan-6-ones rearrange to give 3-iodocycloheptanones on treatment with iodotrimethylsilane. Zinc(II) iodide or mercury(II) halides as catalysts enhance the rate and the selectivity of the reaction.31 If a second, enolizable carbonyl group is present, an intramolecular alkylation may follow the ring enlargement under these reaction conditions.32 Consecutive treatment with tributyltin hydride/ 2,2 -azobisisobutyronitrile affords reduced, iodo-free cycloheptanones, whilst treatment with l,8-diazabicyclo[5.4.0]undecene yields cycloheptenones.33 Similarly, benzenethiol adds to the central bond of bicyclo[3.2.0]heptan-6-ones in the presence of zinc(II) chloride and hydrochloric acid under anhydrous conditions to form 3-(phenylsulfanyl)cycloheptanones.34... 

---