Tributyltin hydride also

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. 

Acrylonitrile and trlbutyltin hydride were obtained from the Aldrich Chemical Company, Inc., and used without further purification. The use of a large excess of acrylonitrile reduced the amount of reduction by-product (2, 3, 4, 6-tetraacetyl-1, 5-anhydroglucitol). Because tributyltin hydride also reacts with acrylonitrile, a small excess must be used. 

The preparation of the branched C-pyranoside 27, which is structurally related to trichothecenes, has been carried out by treatment of the thionoformate 28 (prepared in several steps from 2,3,4,6-tetra-0-acetyl-2-hydroxy-D-glucal) with tributyltin hydride. Also described are the tricyclic compounds 29, prepared from an intermediate used for the synthesis of 27. 

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). 

Our group has also reported that the alkylation products of 4-cyano-l,3-diox-anes can serve as substrates for radical atom transfer reactions [41]. One such example is shown below (Eq. 17). Slow addition of tributyltin hydride/AIBN to a refluxing solution of cyanohydrin 115 generated the radical nitrile transfer product 116. This method, though somewhat limited in scope, can provide access to syn-l,3-diols which maybe unstable to the vigorous Li/NHg reduction conditions. 

Tributyltin hydride was freshly prepared by the method of Hayashi et al.4 Commercial iributyltin hydride (Aldrich Chemical Company, Inc.) can also be used, but in this case the yield of product is 5-7% lower. 

Tributyltin hydride reduction of carbonyl compounds. The reduction of carbonyl compounds with metal hydrides can also proceed via an electron-transfer activation in analogy to the metal hydride insertion into TCNE.188 Such a notion is further supported by the following observations (a) the reaction rates are enhanced by light as well as heat 189 (b) the rate of the reduction depends strongly on the reduction potentials of ketones. For example, trifluoroacetophenone ( re<1 = —1.38 V versus SCE) is quantitatively reduced by Bu3SnH in propionitrile within 5 min, whereas the reduction of cyclohexanone (Erea — 2.4 V versus SCE) to cyclohexanol (under identical... 

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 one study, Ingold and coworkers166 measured the rate constants for the reactions of several alkyl radicals with tributyltin hydride using a laser flash photolytic technique and direct observation of the tributyltin radical. They also used this technique with tributyltin deuteride to determine the primary hydrogen-deuterium kinetic isotope effects for three of these reactions. The isotope effects were 1.9 for reaction of the ethyl radical, and 2.3 for reaction of the methyl and n -butyl radicals with tributyltin hydride at 300 K. 

The same chemical transformation was also realized later by radical reaction using tributyltin hydride and azoisobutyronitrile <1999ACS913>, although the yield was moderate and the ratio of the reduced by-products was much higher (45%). 

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-... 

Chloropyridinecobaloxime(III) 279 also serves as a convenient source of nucleophilic cobalt, and as a means of promoting radical cyclizations [77]. For example, its reduction in the presence of a bromoalkyne such as 280 leads to the formation of a radical 281 which closes onto the alkyne, leading eventually to the ,Z-alkenes 283 and 284 in an 81% yield. Cyclizations of this type are obviously complementary to those effected using tributyltin hydride. 

In a radical reaction of 2-iodomethylpiperidine (112) with tributyltin hydride, 2-(3-phenyl-2-propenyl)piperidine (113) and a 1 1 mixture of epi-mers of perhydropyrido[l,2-6][l,2]thiazine-l,1-dioxide (114) were obtained in 18 and 47% yield, respectively (77TL635). An identical mixture of 113 and the two epimers of 114 was also obtained from a 7 4 mixture of the Z and E isomers of 112, indicating that the starting C=C geometry is not maintained in the product 114. 

The 2,5-dibromo-2,5-dideoxy-D-xylono-1,4-lactone (6) (Scheme 2) can also be selectively reduced to give 5-bromo-2,5-dideoxy-D-fhreo-pentonolactone (7) by reaction with either aqueous hydrazine as mentioned above, or by consumption of 1 mole of hydrogen [ 14]. Further reaction with hydrogen and Pd/C leads to 3-hydroxypentanoic acid by an initial reductive elimination [15]. Reduction of the primary bromine in these cases can be obtained by means of tributyltin hydride [25] to give 8. 

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. 

Vinylic radicals, generated by tributyltin hydride addition on triple bonds, also add on 2,3 double bonds [80,81]. One advantage of this method is the presence of a tributylstannyl-... 

To 244 mg (0.64 mmol) of the starting bromide (E/Z ratio 1 7) in dry toluene (0.015 M) under reflux was added 2.4 eq of tributyltin hydride and AIBN (catalytic amount) in 3 h through a syringe pump. The reaction mixture was cooled and the solvent was evaporated. The residue was dissolved in ether and 10% aqueous KF solution was added, and the mixture was stirred for 18 h. The organic phase was separated, dried, and evaporated. After flash chromatography (hexane-ethyl acetate, 90 10) of the residue gave the 134 mg (80%) of the product mp 75-77°C [a]D —61° (c 1.2, CHC13). Minor amounts of the noncyclized reduction product and the isomeric compound with an a-CHjCOjMe were also isolated. 

The conversion of dithioesters into aldehydes is also easily realized through reduction to a mixed dithioacetal by tributyltin hydride [264]. 

Tributyltin hydride, 316 Tributyltinlithium, 319 Trichloroacetonitrile, 321 Other carbohydrates (Diethylamino)sulfur trifluoride, 110 Triethyloxonium tetrafluoroborate, 44 Carbonates (see also Enol carbonates) Carbon dioxide, 65 Di-/-butyl dicarbonate, 94 Carboxylic acids (see also Dicarbonyl compounds, Unsaturated carbonyl compounds)... 

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