Tributyl reactions

For solvent extraction of a tetravalent vanadium oxyvanadium cation, the leach solution is acidified to ca pH 1.6—2.0 by addition of sulfuric acid, and the redox potential is adjusted to —250 mV by heating and reaction with iron powder. Vanadium is extracted from the blue solution in ca six countercurrent mixer—settler stages by a kerosene solution of 5—6 wt % di-2-ethyIhexyl phosphoric acid (EHPA) and 3 wt % tributyl phosphate (TBP). The organic solvent is stripped by a 15 wt % sulfuric acid solution. The rich strip Hquor containing ca 50—65 g V20 /L is oxidized batchwise initially at pH 0.3 by addition of sodium chlorate then it is heated to 70°C and agitated during the addition of NH to raise the pH to 0.6. Vanadium pentoxide of 98—99% grade precipitates, is removed by filtration, and then is fused and flaked. 

Reactions involving ions can be favored to occur in the organic phase by use of phase-transfer catalysts. Thus the conversion of 1-chlorooctane to 1-cyanooctane with aqueous NaCN is vastly accelerated in the organic phase by 1.3 percent of tributyl (hexadecyl) phosphonium bromide in the aqueous phase. (Starks and Owens, J. Am. Chem. Soc., 95, 3613 [1973]). A large class of such promotions is known. 

Dissolve in Et20, add quinol (500mg for 300mL), dry over Na2S04, filter, evaporate and distil under dry N2. It is a clear liquid if dry and decompose very slowly. In the presence of H2O traces of tributyl tin hydroxide are formed in a few days. Store in sealed glass ampoules in small aliquots. It is estimated by reaction with aq NaOH when H2 is liberated. CARE stored samples may be under pressure due to liberated H2. [J Appl Chem 7 366 1957.]... 

Both allylstannane transmetalation and thermolysis of homoallyl stannoxanes have been used to prepare 2-butenyltin halides as (E)j(Z) mixtures44-45. The reaction between 2-butenyl-(tributyl)stannane and dibutyltin dichloride initially provides dibutyl(l-methyl-2-propenyl)tin chloride as the kinetic product by an SE2 process, but this isomerizes under the reaction conditions to give a mixture containing the (Z)- and (E)-2-butenyl isomers46. 

These observations were explained in terms of an SE reaction between the 2-butenyl-(tributyl)stannane and tin(IV) chloride, which competes with Lewis acid catalyzed carbonyl attack. The 1 -methyl-2-propenyltin trichloride so formed reacts with the aldehyde to give linear products, or isomerizes to give the more stable ( )- and (Z)-2-butenyltin trichlorides which then react74. Similar results were obtained with titanium(lV) chloride, except that the anti-ad-duct was the major product from the butenyltitanium intermediate74. 

Transmetalation to give l-methyl-2-propenylaluminum followed by isomerization to 2-butenyl isomers may be involved in reactions between aldehydes and 2-butenyl(tributyl)-stannane induced by aluminum(III) chloride in the presence of one mole equivalent of 2-propanol. Benzaldehyde and reactive, unhindered, aliphatic aldehydes give rise to the formation of linear homoallyl alcohols, whereas branched products are obtained with less reactive, more hindered, aldehydes66,79. 

Excellent chelation control was observed using tributyl(2-propenyl)stannane and a-benzyloxy-cyclohexaneacetaldehyde with magnesium bromide or titanium(IV) chloride, whereas useful Cram selectivity was observed for boron trifluoride-diethyl ether complex induced reactions of the corresponding ferr-butyldimethylsilyl ether89. 

The boron trifluoride-diethyl ether complex induced reaction of 2-butenyl(tributyl)-stannane and 3-(/er/-butyldimethylsilyloxy)-2-methylpropanal gave predominantly the nonchelation-controlled yyn-product93, whereas with the analogous 3-benzyloxyaldehyde, 2-propenyl-tin trichloride, generated in situ from tributyl(2-propenyl)stannanc and tin(IV) chloride, gave the chelation-controlled product93. 

The reaction between 5-methyl-2-(l-methyl-1 -phenylethyl)cyclohexyl 2-oxoacetate and 2-buteny](tributyl)stannane promoted by boron trifluoride-diethyl ether complex showed a strong preference for 57-facial attack, with syn selectivity69. 

The Lewis acid mediated addition of allylic tin reagents to nitroalkenes has been reported. The condensation reaction of tributyl[(Z)-2-butenyl]tin(IV) with (E)-(2-nitroethenyl)benzene or (L)-l-nitropropene catalyzed by titanium(IV) chloride proceeded with modest anti diastereoselectivity. Poorer diastereoselection resulted when diethyl ether aluminum trichloride complex was employed as the Lewis acid 18. 

These results are in accordance with the findings of Boothe and coworkers26, who found that the reactions of four diastereomeric 2-bromo-3-phenylsulfinylbutanes with tributyl-tin radicals generate /3-phenylsulfinyl sec-butyl radicals (8) which eliminate PhSO radicals to form the 2-butenes in a stereoselective manner. The stereoselectivities observed in this free radical elimination must result from the fact that the rate constant for elimination is greater than that for rotation about the C—C bond. Furthermore, a neighboring phenyl group on the radical center seems to stabilize the radical enough so that the internal rotation can compete with the -elimination reaction. It is also noteworthy that the small... 

In the frame of a medicinal project at J J Pharmaceutical Research and Development aimed at designing new potent and selective glycogen synthase kinase-3/i (GSK-3/3) inhibitors, the C-3 derivatization of the 1-methyl-4-[l-alkyl-lff-indol-3-yl]-lff-pyrrole-2,5-dione scaffold was explored [31]. Microwave-assisted Stille reaction of 3-chloro-l-methyl-4-[l-alkyl-lff-indol-3-yl]-lH-pyrrole-2,5-diones with (2,4-dimethoxy-5-pyrimidinyl)(tributyl) stannane at 200 °C yielded in 6 min the desired 3,4-diaryl-lff-pyrrole-2,5-diones in moderate yields (Scheme 12). 

The kinetics of the reactions of tributyl- and triphenylphos-phines with alkyl azides show that steric hinderance is not a sig-... 

Tributyl(4-methoxyphenyl)stannane (2) is added to the reaction flask via a 30-mL syringe. 

C. 4-Methoxy-4 -nitrobiphonyl (3). A dry, 500-mL, three-necked, round-bottomed flask equipped with a reflux condenser, magnetic stirring bar, nitrogen gas inlet, and rubber septum (Note 1) is charged sequentially with 300 mL of anhydrous N,N-dimethylformamide (Note 13), 15.0 g (55.4 mmol) of 4-nitrophenyl trifluoromethanesulfonate (1), 27.8 g (70.0 mmol) of tributyl(4-methoxyphenyl)stannane (2) (Note 14), 7.5 g of dry lithium chloride (Note 15), and 1.6 g (4 mol percent) of bis(triphenylphosphine)palladium(ll) chloride (Note 16). The rubber septum is replaced with a Teflon stopper and the yellow mixture is heated at 100-105°C for 2.5 hr. After approximately 20 min, the reaction turns dark brown. 

Chlorophenyl)-4-phenyl-l,2,5-thiadiazole 128 was prepared from 3-trifluoromethylsulfonyloxy-4-phenyl-1,2,5-thiadiazole 127 by palladium-catalyzed cross-coupling reaction with the tributyl(4-chlorophenyl)stannane (Equation 20) <1996H(43)2435>. The addition of lithium chloride improves the yield. The 3-chloro- and 3-bromo-l,2,5-thiadiazole derivatives were also reactive, but only the bromo compound gave the product in comparable yield (see Section 5.09.7.6). 

The reactions of dichlorocarbene with phosphorus ylides result in the corresponding olefins and phosphines.66-68 In the reaction of dichlorocarbene generated in situ with tributyl- and triphenylmethylenephosphoranes or triphenylethylidenephosphorane, the olefin yield increases as the nucleo-philicity of phosphorus ylide increases. According to,67 the reaction starts from the electrophilic attack of carbene at the a-C atom of phosphorus ylide. Then the intermediately formed betaine (28) (Scheme 14) decomposes to eliminate the phosphine molecule and form dichloroolefin (29). 

Iodoacetylene (prepared in situ from ethynylmagnesium bromide or tributyl (ethynyl)tin with iodine) was used as a dipolarophile in the 1,3-dipolar cycloaddition reactions with nitrile oxides to produce 2-(5-iodoisoxazol-3-yl)pyridine and 3-(4-fluorophenyl)-5-iodoisoxazole in good yield (70%-90%). Subsequently,... 

In the presence of a chiral promoter, the asymmetric aldol reaction of pro-chiral silyl enol ethers 71 with prochiral aldehydes will also be possible (Table 3-6). In this section, a chiral promoter, a combination of chiral diamine-coordinated tin(II) triflate and tributyl fluoride, is introduced. In fact, this is the first successful example of the asymmetric reactions between prochiral silyl enol ethers and prochiral aldehyde using a chiral ligand as promoter. 

Miki effected Pd-catalyzed cross-coupling between dimethyl 7-bromoindole-2,3-dicarboxylate and both tributylvinyltin and tributyl-1-ethoxyvinyltin to yield the expected 7-vinylindoles [197]. Hydrolysis of the crude reaction product from using tributyl-1-ethoxyvinyltin gave the 7-acetylindole. Sakamoto used dibromide 192, which was prepared by acylation of 7-bromoindole, in a very concise and efficient synthesis of hippadine [36]. The overall yield from commercial materials is 39%. Somewhat earlier, Grigg employed the same strategy to craft hippadine from the diiodoindoline version of 192 using similar cyclization reaction conditions ((Me3Sn)2/Pd(OAc)2), followed by DDQ oxidation (90%) [198]. 

Sakamoto described similar reactions of o-bromoaniline derivatives with (Z)-tributyl-2-ethoxyvinyltin and subsequent cyclization of the coupled product with TsOH to yield, for example, N-acetylindole (29% yield overall) [185], This research group also used this methodology to synthesize a series of azaindoles, an example of which is illustrated below [204]. Halonitropyridines were particularly attractive as coupling partners with tributyl-2-ethoxyvinyltin and precursors to azaindoles. Although the (Z)-isomer of 202 is obtained initially, it isomerizes to the ( )-isomer which is the thermodynamic product. This strategy represents a powerful method for the synthesis of all four azaindoles (l//-pyrrolopyridines). In fact, this method, starting with 2,6-dibromoaniline, is one of the best ways to synthesize 7-bromoindole (96% overall yield) [36]. 

The thermal decomposition of liquid tributyl phosphate at 178-240 °C may be followed by the rate of formation of dibutylphosphoric acid. Below 3% decomposition the reaction is first-order. At higher acid concentrations acid catalysis is observed. The main reaction seems to be dealkylation... 

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