Tributyltin esters

TWO organometallic polymers previously developed, tributyl-tin methaczylate/methyl methacrylate copolymer (TBTM/MeM) and the tributyltin ester of methyl vinyl ether/maleic anhydride (TBT-MVEt-MAn), were selected for use as wood impregnants. Full Cell and Enpty Cell Methods were used to treat wood with TBTCVMeM in "Rule 66" mineral spirits and in combination with P13 creosote. Although the polymers seem to be miscible with the creosote, this combination results in only surface penetration of wood when... 

The esterification of bis(tri- -butyltin) oxide (TBTO) with acids leads to tributyltin esters ... 

The esterification of bis(tri-n-butyltin) oxide (TBTO) with carboxylic acids leads to tributyltin esters (n-but.)3Sn O-Sn(n-but.)3 + 2 R-COOH R-COO-Sn(n-but.)3 + H2O... 

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). 

Tributyltin hydride is used for hydrogenolysis of allylic esters[369-372]. 

Poller (498, 544) prepared a number of tributyl- and triphenyl-stan-nyl esters of sucrose hydrogenphthalate and succinate, and found that, as potential antifoulants, these were at least three times as effective against the marine alga, Enteromorpka, as bis(tributyltin) oxide, even though they contain almost one third the tin (see Table VIII). A new antifouling paint that also contains tributyltin compounds has recently been developed in Norway (545). 

Thermal decarboxylation of pyrimidylcarboxylic organotin esters is another means to prepare the corresponding stannylpyrimidines [33]. This method obviates the intermediacy of lithiated pyrimidine species that would undergo undesired reactions at higher temperatures. The decarboxylation occurs at the activated positions. Therefore, thermal decarboxylation of tributyltin carboxylate 62, derived from refluxing carboxylic acid 61 with bis(tributyltin) oxide, provided 4-stannylpyrimidine 63. Addition of certain Pd(II) complexes such as bis(acetonitrile)palladium(II) dichloride improved the yields, whereas AIBN and illumination failed to significantly affect the yield. 

Bis(tribuyltin) oxide reacts with carboxylic esters in ether at room temperature to give the corresponding tributyltin carboxylate and tributyltin alkoxide, and this reaction is recommended for removing protecting ester groups in the presence of other functional substituents.358-360... 

Intermediates such as 224 resulting from the nudeophilic addition of C,H-acidic compounds to allenyl ketones such as 222 do not only yield simple addition products such as 225 by proton transfer (Scheme 7.34) [259]. If the C,H-acidic compound contains at least one carbonyl group, a ring dosure is also possible to give pyran derivatives such as 226. The reaction of a similar allenyl ketone with dimethyl mal-onate, methyl acetoacetate or methyl cyanoacetate leads to a-pyrones by an analogous route however, the yields are low (20-32%) [260], The formation of oxaphos-pholenes 229 from ketones 227 and trivalent phosphorus compounds 228 can similarly be explained by nucleophilic attack at the central carbon atom of the allene followed by a second attack of the oxygen atom of the ketone at the phosphorus atom [261, 262], Treatment of the allenic ester 230 with copper(I) chloride and tributyltin hydride in N-methylpyrrolidone (NMP) affords the cephalosporin derivative 232 [263], The authors postulated a Michael addition of copper(I) hydride to the electron-... 

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 synthesis of valsartan (2) by Novartis/Ciba-Geigy chemists is highlighted in Scheme 9.5. Biphenylbenzyl bromide 18 is converted to biphenyl acetate 19 in the presence of sodium acetate in acetic acid. Hydrolysis of 19 followed by Swern oxidation delivered the biphenyl aldehyde 20, which underwent reductive amination with (L)-valine methyl ester (21) to give biphenyl amino acid 22. Acylation of 22 with penta-noyl chloride (23) afforded biphenyl nitrile 24, which is reacted with tributyltin azide to form the tetrazole followed by ester hydrolysis and acidihcation to provide valsartan (2). [See Biihlmayer et al. (1994, 1995).]... 

The short Sanofi route to irbesartan (3) is outlined in Scheme 9.6. Dihydroimidazolone 27, which is prepared from the reaction of 1-amino-cyclopentanecarboxylic acid ester (25) with ethyl pentanimidate (26) in the presence of acetic acid in refluxing xylene, is alkylated with biphenylbenzyl bromide 18 in the presence of sodium hydride in DMF to give 28. Finally, the synthesis of irbesartan (3) is completed by the tetrazole formation from reaction of the nitrile group of 28 with tributyltin azide in refluxing xylene. [See Bernhart et al. (1993a, b).]... 

Barton-McCombie deoxygenation is not always stereoselective the diastereo-meric ratios strongly depends on the nature of the protecting groups and of the ester moiety. However, in 2-C-trifluoromethyl-2-deoxyfuranose, the a compound is the major product of the reaction, due to steric hindrance of this a side. In 3-C-trifluoromethyl-3-deoxyfuranose, deoxygenation by tributyltin hydride yields only the a product, if it is performed with oxalate instead of thiocarbonate. Another possibility to obtain this selectivity is to perform the reaction with 1,2,5,6-di-O-isopropylidene-a-D-glucofuranose (Figure 6.34). ... 

The seemingly complex imidazolone (78-3) is in fact obtained in a single step by reaction of the amino-ester (78-1) with the iminoether (78-2) derived from capro-nitrile. The relatively acidic proton on the heterocyclic ring is next removed by reaction with sodium hydride. This anion is then alkylated with the same biphenyl-methyl bromide (77-2) that was used to prepare losartan to afford (78-4). The nitrile group is in this case converted to the tetrazole by means of tributyltin azide, a reagent that involves milder conditions than the traditional acidic medium used to generate hydrazoic acid. Thus, treatment of (78-4) with the tin reagent affords irbesartan (75-5) [82]. 

C. (Z)-3-Tributylstannylmethylene-4-iaopropyl-l, 1-eyclopentanediear-boxylie aoid, dimethyl ester (3). A flame-dried, 100-mL, round-bottomed flask equipped with a magnetic stirring bar is charged with argon, and 23.8 g (0.100 mol) of dialkylmalonate diester (2), 30.2 g (< 0.104 mol) of tributyltin hydride (Note 11), and 40 mg (0.25 mmol) of azobisisobutyronitnle (AIBN) (Note 12) are added neat (Notes 13, 14). The entire assembly is lowered into an oil bath maintained at 75-85°C, and the mixture is stirred. After an induction period of less than 30 min, an exothermic reaction occurs which produces a small amount of gas and a rise in the temperature of the oil bath (as much as 20°C for a small bath). After this point TLC shows that the reaction is essentially complete (Notes 15, 16, 17). Unpurified 3 thus obtained is suitable for protodestannylation. 

The cyclopropane is inert to tributyltin chloride, but reacts readily with more highly Lewis acidic tributyltin trifluoromethanesulfonate (triflate) [11]. The 3-stannyI ester 13 showed no sign of internal chelation Eq. (16). 

The tributyltin hydride reduction usually proceeds without complications. The most common byproduct is starting alcohol, which is postulated to be derived from a mixed thioacetal. Use of the phenyl thionocarbonate ester has been reported to minimize this side reaction in cases where it is a problem.6... 

The facile formation of the iodo compound, and the subsequent reduction with tributyltin hydride opens a new access to 2-amino-2,3-dideoxy-D-glucose (D-lividosamine) present in various aminoglycoside antibiotics [92], The same strategy been used in the synthesis of C-lO -C-l fragment of boromycin [93]. Displacement of the C-3 imidazylate ester of a 2-azido-2-deoxy-a-D-altropyranose derivative with benzoate occurred readily [94], compared with the corresponding tosylate [95],... 

The simple addition reaction in Scheme 19 illustrates how the notation is used. Ester (1) can be dissected into synthons (2), (3) and (4). Synthons for radical precursors (pro-radicals) possess radical sites ( ) A reagent that is an appropriate radical precursor for the cyclohexyl radical, such as cyclohexyl iodide, is the actual equivalent of synthon (2). By nature, alkene acceptors have one site that reacts with a radical ( ) and one adjacent radical site ( ) that is created upon addition of a radical. Ethyl acrylate is a reagent that is equivalent to synthon (3). Atom or group donors are represented as sites that react with radicals ( ) Tributyltin hydride is a reagent equivalent of (4). In practice, such analysis will usually focus on carbon-carbon bond forming reactions and the atom transfer step may be omitted in the notation for simplicity. 

The driving force for the fragmentation is formation of the C=0 double bond. If R reacts with Bu3SnH, a tributyltin radical is produced which continues the chain. Carried out in this manner this reaction is called the Barton deoxygenation of alcohols, since alcohols are precursors for the thiono esters. 

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