Triphenyltin hydrides

Triphenyltin chloride, 7.49 g. (0.019 mole) in 150 ml. of purified monoglyme, is allowed to react with sodium boro-hydride (3.3 g., 0.087 mole) in 150 ml. of purified monoglyme 

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The wide variety of methods available for the synthesis of orga-noselenides,36 and the observation that the carbon-selenium bond can be easily cleaved homolytically to give a carbon-centered radical creates interesting possibilities in organic synthesis. For example, Burke and coworkers have shown that phenylselenolactone 86 (see Scheme 16), produced by phenylselenolactonization of y,S-unsaturated acid 85, can be converted to free radical intermediate 87 with triphenyltin hydride. In the presence of excess methyl acrylate, 87 is trapped stereoselectively, affording compound 88 in 70% yield 37 it is noteworthy that the intramolecular carbon-carbon bond forming event takes place on the less hindered convex face of bicyclic radical 87. 

It is important to emphasize that the hydroxy dithioketal cyclization can be conducted under mild reaction conditions and can be successfully applied to a variety of substrates.15 However, the utility of this method for the synthesis of didehydrooxocane-contain-ing natural products requires the diastereoselective, reductive removal of the ethylthio group. Gratifyingly, treatment of 13 with triphenyltin hydride and a catalytic amount of the radical initiator, azobisisobutyronitrile (AIBN), accomplishes a homolytic cleavage of the C-S bond and furnishes didehydrooxocane 14 in diastereo-merically pure form (95 % yield), after hydrogen atom transfer. 

Trimethyltin hydride has been shown to add to trimethylvinyltin, and triethyltin hydride to triethylvinyltin, to give both the 1,1- and the 1,2-distannylethanes, whereas triphenyltin hydride reacts with triphenyl vinyltin to give only the 1,2-adduct (180). 

Similarly, triphenyltin hydride reacts with diethylzinc or diethyl-cadmium in a strongly solvating solvent, such as oxolane (tetrahydro-furan) or 1,2-dimethoxyethane, to give the solvated, metal-metal-bonded products (272). 

Likewise, triphenyltin hydride reacts with ethylzinc chloride, or triphenyltin chloride with metallic zinc, to give the compound PhaSnZnCl, which is stable in the presence of a strongly coordinating ligand, but, in its absence, apparently undergoes an intermetallic shift of the organic group, so that protic acids react to liberate benzene (272). 

Aldehydes and ketones can be converted to ethers by treatment with an alcohol and triethylsilane in the presence of a strong acid or by hydrogenation in alcoholic acid in the presence of platinum oxide. The process can formally be regarded as addition of ROH to give a hemiacetal RR C(OH)OR", followed by reduction of the OH. In this respect, it is similar to 16-14. In a similar reaction, ketones can be converted to carboxylic esters (reductive acylation of ketones) by treatment with an acyl chloride and triphenyltin hydride. " ... 

The nucleophilic displacement of the iodine moiety in 2-iodoben-zoates mediated by triphenyltin hydride and di-n-butyltin dichloride in aqueous solution has been demonstrated (Eq. 6.16).33 For example, 2-iodobenzoic acid reacts with a toluene solution of Ph3SnH/l,3-(N02)2 C6H4/aq. NaHC03 to give 89% yield of salicylic acid. 

An example of asymmetric synthesis involving cycloaddition of an azide to dimethyl acetylenedicarboxylate is depicted in Scheme 172. Thus, asymmetric auxiliary 1042 reacts with styrene and sodium azide to generate azide 1043 in 90% yield and 94% diastereomeric purity. The following reaction (Scheme 172) with dimethyl acetylenedicarboxylate converts azide 1043 into triazole 1044 in 75% yield. Finally, the bond with selenium is cleaved by treatment with triphenyltin hydride and AIBN to furnish triazole 1045 in 80% yield and preserved optical purity (94%) <2003AGE3131>. 

The few cases in which thermodynamic control is not effective appear to be dominated by steric effects39. Thus, trapping of radical 25 with triphenyltin hydride regioselec-tively yields product 26, in which the double bond is separated from the ester through a methylene bridge (equation 12). 

Monohalomonohydrotin compounds can be prepared in excellent yields by reactions of triphenyltin hydrides with dialkyl- or diphenyltin dihalides345 ... 

John and coworkers78 also observed cyclization to a five-membered ring heterocycle in their hydride reduction of methyl 6/i-isothiocyanatopenicillanate with both tributyltin hydride and triphenyltin hydride (Scheme 16). John and coworkers also found this type of ring closure when an isocyanide was reduced with tributyltin deuteride. The mechanism of this arrangement (Scheme 17) has been confirmed by deuterium labelling. 

In addition, Kozuka and Lewis measured the tritium isotope effect for the reaction between the n -hexyl, the 2-hexyl and the 2-methy 1-2-pentyl radicals with triphenyltin hydride and triphenyltin hydride-t see the last three entries in Table 11. The isotope effect of 2.55 found for the triphenyltin hydride-w-hexyl radical reaction was slightly smaller... 

Calculated using the expression k jk = riil/L)) 447 (Reference 170). Measured using triphenyltin hydride rather than tributyltin hydride. 

Addition to thionolactones cyclic ethers. A wide variety of alkyliithium reagents add to the C=S group of thionolactones. The adducts, after reaction with CH,I, can be isolated in high yield as mixed methyl thioketals. The methylthio group can be removed by reduction with triphenyltin hydride (AIBN) to give cyclic ethers. The reaction is not dependent on the ring size and can be stereoselective, as shown by the synthesis of the ether lauthisan (2) from a thionolactone (1). 

Phenyl aUcyl tellurides are reduced by triphenyltin hydride under mild conditions, giving the corresponding hydrocarbons in high yields. An excess of the reagent is necessary (2-2.8 equiv), but a radical initiator need not be employed. 

Bromonaphthalene has been reduced to naphthalene in good yield by hydrogenation over Raney nickel in methanolic potassium hydroxide, by triphenyltin hydride in benzene, by magnesium in isopropyl alcohol, by sodium hydrazide and hydrazine in ether, and by copper(I) acetate in pyridine. ... 

On treatment with benzeneselenenyl chloride two olefinic urethanes (214 and 217) underwent cyclization to afford piperidine derivatives (215 and 218, respectively) having the cis stereochemistry. Their reduction with triphenyltin hydride gave the same product (216). Removal of the blocking group from the nitrogen gave ( )-isosolenopsin A (Ic) (Scheme 6) (392). 

Heating the alkyne 9 in the presence of toluene results in the formation of the bicyclic P-lactam 10 in moderate yield (Scheme 1) <99CC1913>. However, reaction in benzene in the presence of AIBN and triphenyltin hydride results in the formation of 11 (R = SnPhs) as the Z isomer in almost quantitative yield. If triphenyltin is replaced by PhSH the yield of 11 ( R= SPh) is much reduced and both Z and E isomers are formed... 

The 4-hydroxy-(S)-proline-derived acid (232) was subjected to electrophilic lactoni-zation either with J2-KJ-NaHC03 to yield the iodolactone (233a), or benzeneselenyl chloride to give the phenylselenolactone (23b). Reductive removal of X from these products was achieved with tri-n-butyl- or triphenyltin hydride, followed by hydro-genolysis to yield (234) with at least 99% optical purity 231 j). 

The work so far described has been dependent on the Sn-H bond in tributyltin hydride. Triphenyltin hydride can also be employed [lie,Ilf], The unusual efficiency of triphenyltin hydride for the desulfnrization of thiocarbonyl compounds has only recently been reported [12]. There are specialized texts on organotin compounds [13] in which the properties of the Sn-H bond are discussed at length. 

Although tributyltin and triphenyltin hydrides are excellent reagents for radical chemistry, they have the disadvantage that they are costly and of relatively high molecular weight. For small operations, in the laboratory, this is not serious. However, there is a major additional problem, particularly for industrial use, because of the toxicity of these tin compounds and because of the difficulty of removing tin dimers that are formed as by-products [13]. Similar comments apply to germanium hydrides, which are even more expensive [21]. 

Tri-n-bytylin hydride 60,64,71,104 Trimethylsolfonium methylsulfate 143 Triphenyltin hydride 104 Tris(phenylthio)aluminium 20 T rithiocarbonates... 

The preceding compound (125 mg, 0.46 mmol) was stirred together with triphenyltin hydride (0.29 mmol, 1.15 mmol) and AIBN (5 mg) in toluene (8 ml) at reflux temperature for 20 min. Concentration and silica gel chromatography (2% ether in petroleum ether) gave the title ether (95.6 mg, 92%). 

Fluoro-l-phenylethanone is also reduced by triphenyltin hydride in a 2,2 -azobisisobutyroni-trile initiated reaction to yield almost exclusively acetophenone. The selectivity decreases as the solvent becomes more polar.96 Electrolytic reduction of 2,2,2-trifiuoro-l-phenylethanone (8) does not proceed to the expected trifluoromethylated pinacol, but results in acetophenone and/or acetophenone pinacol depending on the potential employed the reaction time controls the product ratio.97... 

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