Hydride, tributyltin

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). 

The /3,7-unsaturated aldehyde 407 is prepared in good yields by the carbo-nylation of an allylic chloride under mild conditions using tributyltin hydride as a hydride source[261]. Aldehydes are obtained in moderate yields by the reaction of CO and H2[262],... 

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

Methylation of avermectins B and B2 leads to the corresponding derivatives of the A series (49). A procedure involving the oxidation of the 5-methoxy group with mercuric acetate and NaBH reduction of the 5-keto-intermediate allows the conversion of the A to the B components (50). The 23-hydroxy group of the "2" components, after selective protection of the other secondary hydroxy groups, is converted to a thionocarbonate, which can be elirninated to give the 22,23-double bond of the "1" components alternatively it can be reduced with tributyltin hydride to the 22,23-dihydro derivatives (= ivermectins) (51). 

Cyclopropenone was flrst synthesized " by the hydrolysis of an equilibrating mixture of 3,3-dichlorocyclopropene and 1,3-dichloro-cyclopropene (prepared by reduction of tetrachlorocyclopropene with tributyltin hydride). This procedure has been adapted - to prepare... 

Alkyl halides can be reduced to alkanes by a radical reaction with tributyltin hydride, (C4H9)3SnH, in the presence of light (hv). Propose a radical chain mechanism by which the reaction might occur. The initiation step is the light-induced homolytic cleavage of the Sn— H bond to yield a tributyltin radical. 

Tributyltin hydride, reaction with alkyl halides. 358 Tricarboxylic acid cycle, see Citric acid cycle... 

The reaction of 5-chloro-l,4-benzoxazepine (4), whose preparation is described below, with tributyltin hydride catalyzed by tetrakis(triphenylphosphane)palladium(0) gives 1,4-benzox-azepine (5).32... 

A solution of 3.7I g (0.013 mol) of tributyltin hydride in 10 mL benzene is added dropwise to a solution of 3.09 g (0.011 mol) of S-[(S)-4-(benzyloxy)-3-pentenyl] 5-methyl carbonodithioate in 25 mL of degassed, anhyd benzene under an atmosphere of argon, followed by 5 mg of AIBN. The mixture is heated under reflux for 2.5 h and then is concentrated under reduced pressure. Flash chromatography of the residue using ht,0/petroIeum ether 1 50 containing 1 % triethylamine as eluant gives a colorless oil yield 3.87 g (78%) [a] - 26 (e = 1. CHCl3). 

A solution containing 447 mg (1.38 mmol) of 3-(4-mcthylphenylsulfonyl)-1-nonene, 928 mg (3.19 mmol) of tributyltin hydride, and 10 mg of AIBN. in dry benzene is heated under reflux under an atmosphere of nitrogen for 2 h. Concentration under reduced pressure and chromatography on neutral alumina using benzene as eluant gives the product yield 443 mg (65%) further purification by distillation, bp 136-142X/0.003 Torr. 

Stannylation of lithiated allyl ethers gives (Z)-3-alkoxyallylstannanes (1)115,116, whereas mixtures of (Z)- and ( )-tributyl(3-methoxy-2-propenyl)stannanes (2) were obtained from free-radical addition of tributyltin hydride to l-methoxy-l,2-propadienel16. 

Radical Diels-Alder reactions have been used mainly to synthesize polycyclic molecules. These reactions, like those that involve cations and anions as components, proceed quickly but generally do not give high yields. Thus, the tricyclic enone 14 is the result of an intramolecular Diels-Alder reaction of quenched vinyl radical intermediate 13 obtained by treating the iododienynone 12 with n-tributyltin hydride/2,2 -azobisisobutyronitrile (AIBN) [28] (Equation 1.11). 

The reaction of tributyltin hydride with ring-substituted benzyl chlorides gives a Hammett p-factor of -1-0.81, confirming the "nucleophilic character of the BusSn- radical (303). 

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. 

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. 

Quebrachitol was converted into iL-c/j/roinositol (105). Exhaustive O-isopropylidenation of 105 with 2,2-dimethoxypropane, selective removal of the 3,4-0-protective group, and preferential 3-0-benzylation gave compound 106. Oxidation of 106 with dimethyl sulfoxide-oxalyl chloride provided the inosose 107. Wittig reaction of 107 with methyl(triphenyl)phos-phonium bromide and butyllithium, and subsequent hydroboration and oxidation furnished compound 108. A series of reactions, namely, protection of the primary hydroxyl group, 0-debenzylation, formation of A-methyl dithiocarbonate, deoxygenation with tributyltin hydride, and removal of the protective groups, converted 108 into 7. 

The stereospecific base-cleavage of the trimethylsilyl group in 1,3-dithiane 1-oxides 499 enables to obtain the specifically deuteriated products 500 (equation 303), A nitro group in y-nitroalkyl sulphoxides 501 (obtained by the Michael addition of nitroalkanes to a, j8-unsaturated sulphoxides) is replaced by hydrogen by means of tributyltin hydride (equation 304). This reagent does not affect the sulphinyl function. The overall procedure provides an efficient method for the conjugate addition of alkyl groups to a, -unsaturated sulphoxides . ... 

The 8-methyl-8,14-cycloberbine 364, derived from the protoberberine 324 via the betaine 363, was reduced with sodium borohydride or lithium aluminum tri-tert-butoxyhydride to give a diastereoisomeric mixture of cis-and trans-alcohols (7.8 1 or 1 7.8, respectively) (Scheme 64).t)n exposure to formaldehyde the mixture underwent N-hydroxymethylation and subsequent intramolecular substitution on the aziridine ring to give the oxazolidine 365. Removal of the hydroxyl group in 365 was accomplished by chlorination followed by hydrogenolysis with tributyltin hydride. Reductive opening of the oxazolidine 366 with sodium cyanoborohydride afforded ( )-raddeanamine (360), which has already been converted to ochotensimine (282) by dehydration. 

---