Tributyltin chloride, reduction

The allylstannane 474 is prepared by the reaction of allylic acetates or phosphates with tributyltin chloride and Sml2[286,308] or electroreduction[309]. Bu-iSnAlEt2 prepared in situ is used for the preparation of the allylstannane 475. These reactions correspond to inversion of an allyl cation to an allyl anion[3l0. 311], The reaction has been applied to the reductive cyclization of the alkenyl bromide in 476 with the allylic acetate to yield 477[312]. Intramolecular coupling of the allylic acetate in 478 with aryl bromide proceeds using BuiSnAlEti (479) by in situ formation of the allylstannane 480 and its reaction with the aryl bromide via transmetallation. (Another mechanistic possibility is the formation of an arylstannane and its coupling with allylic... 

Lithium butyldimethylzincate, 221 Lithium sec-butyldimethylzincate, 221 Organolithium reagents, 94 Organotitanium reagents, 213 Palladium(II) chloride, 234 Titanium(III) chloride-Diisobutylalu-minum hydride, 303 Tributyltin chloride, 315 Tributyl(trimethylsilyl)tin, 212 3-Trimethylsilyl-l, 2-butadiene, 305 Zinc-copper couple, 348 Intramolecular conjugate additions Alkylaluminum halides, 5 Potassium t-butoxide, 252 Tetrabutylammonium fluoride, 11 Titanium(IV) chloride, 304 Zirconium(IV) propoxide, 352 Miscellaneous reactions 2-(Phenylseleno)acrylonitrile, 244 9-(Phenylseleno)-9-borabicyclo[3.3.1]-nonane, 245 Quina alkaloids, 264 Tributyltin hydride, 316 Conjugate reduction (see Reduction reactions)... 

Generating tin hydride in situ by using a catalytic amount of tributyltin chloride and sodium cyanoborohydride [24] did not solve the problem. Although this method inherently produces the desired low concentration of n-BujSnH to promote cyclization over direct reduction of the starting material and reduces drastically the amount of tin residue, a displacement reaction between solvent and the benzylic hydroxyl group takes place. Eventually, the best method was the use of high dilution conditions at approximately 70 °C in benzene followed by the KF workup. 

The reductive desulfonylation of a-sulfonyl esters with tin hydrides only succeeds with n-deficient heterocyclic sulfones (Eq. 104).175 These sulfones are inert under standard procedures using Al/Hg or Na/Hg, but undergo facile C-S cleavage with tin hydrides. Substitution of //-liu3Snl) for n-Bu3SnH gives access to a-deuterated esters.58 A catalytic version of the reaction is carried out with substoichiometric amounts of tributyltin chloride and an excess of poly(methyl-hydrosiloxane) (PMHS) in the presence of potassium fluoride. This method has been employed for the synthesis of 2-fluoroalkanoates (Eq. 105).58... 

The magnesium-mediated reductive trifluoromethylation also works for other structurally diverse chlorosilanes. Chlorotriethyl-silane, f-hutyldimethylsilyl chloride, and tris(trimethylsilyl)silyl chloride have been applied to prepare corresponding trifluoro-methyl-containing silanes. However, the reductive trifluoromethylation did not take place with other electrophiles such as aldehydes, ketones, allyl bromide, benzyl chloride, or tributyltin chloride. Even tributyltin hydride and allyltrimethylsilane showed no reactivity The reason for such behavior is not clear. Probably, chlorosilanes play an important role during the reductive trifluoromethylation both as a silylating agent and a single-electron transfer promoter. 

A full paper on the use of the palladium-catalysed tributyltin hydride reduction of acyl chlorides to aldehydes has appeared. The importance of the palladium species in these reactions is clearly seen during the reduction of the acid chloride (1), which gives citronellal in the presence of catalyst, but yields menthone in its absence (Scheme 3). 

The deamination of primary amines RNH2 (R = CsHn, PhCH2, PhCHMe or PhCH=CHCH2) to the corresponding hydrocarbons is accomplished by conversion into the benzimidoyl chlorides, followed by reduction with tributyltin hydride in the presence of AIBN (equation 121)398. 

Crich and Rumthao reported a new synthesis of carbazomycin B using a benzeneselenol-catalyzed, stannane-mediated addition of an aryl radical to the functionalized iodocarbamate 835, followed by cyclization and dehydrogenative aromatization (622). The iodocarbamate 835 required for the key radical reaction was obtained from the nitrophenol 784 (609) (see Scheme 5.85). lodination of 784, followed by acetylation, afforded 3,4-dimethyl-6-iodo-2-methoxy-5-nitrophenyl acetate 834. Reduction of 834 with iron and ferric chloride in acetic acid, followed by reaction with methyl chloroformate, led to the iodocarbamate 835. Reaction of 835 and diphenyl diselenide in refluxing benzene with tributyltin hydride and azobisisobutyronitrile (AIBN) gave the adduct 836 in 40% yield, along with 8% of the recovered substrate and 12% of the deiodinated carbamate 837. Treatment of 836 with phenylselenenyl bromide in dichloromethane afforded the phenylselenenyltetrahydrocarbazole 838. Oxidative... 

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).]... 

Reduction of acyl chlorides. The known reduction by tributyltin hydride of acyl chlorides to aldehydes (1, 1193) and esters2 when conducted in the presence of Pd[P(CtH5)3]4 is completely selective in favor of the former products and is much more rapid. Yields of aldehydes are 75-95%, even on a preparative scale. 

Reductive coupling of carbonyls to alkenes Titanium(IV) chloride-Zinc, 310 of carbonyls to pinacols Titanium(III) chloride, 302 Titanium(IV) chloride-Zinc, 310 of other substrates Samarium(II) iodide, 270 Reductive cyclization 2-(Phenylseleno)acrylonitrile, 244 Tributylgermane, 313 Tributyltin hydride, 316 Triphenyltin hydride, 335 Trityl perchlorate, 339 Reductive hydrolysis (see Hydrolysis) Reductive silylation Chlorotrimethylsilane-Zinc, 82... 

Finally, when the selective reduction of secondary centers is desired over primary centers, free radical chemistry provides the answer. Unlike ionic mechanisms, the formation of free radicals occurs more readily at tertiary centers, with secondary radicals being more stable than primary radicals. As shown in Scheme 6.72, tributyltin hydride sequentially removed the secondary chloride with complete reduction of both chlorides over extended reaction times [111]. 

O Scheme 26) [196]. Tetra-0-acetyl-D-galactono-l,4-lactone 75 yields 3-deoxylactone 77 through the unsaturated lactone 76. Because of the facial selectivity in the hydrogenation, the 2-acetate group in the product is always cis to the side chain. 2,3-Unsaturated aldono-lactones can also be saturated by 1,4-reduction with tributyltin hydride, copper(I) iodide, and trimethylsilyl chloride [197]. Under these conditions other isolated olefins are not affected. 

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