Tributyltin hydride-2,2 -azobisisobutyronitril

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). 

In the presence of proton and/or Lewis acid and strong nucleophiles bicyclo[3.2.0]heptan-6-ones are converted to 3-substituted cycloheptanones (Table 15). Bicyclo[3.2.0]heptan-6-ones rearrange to give 3-iodocycloheptanones on treatment with iodotrimethylsilane. Zinc(II) iodide or mercury(II) halides as catalysts enhance the rate and the selectivity of the reaction.31 If a second, enolizable carbonyl group is present, an intramolecular alkylation may follow the ring enlargement under these reaction conditions.32 Consecutive treatment with tributyltin hydride/ 2,2 -azobisisobutyronitrile affords reduced, iodo-free cycloheptanones, whilst treatment with l,8-diazabicyclo[5.4.0]undecene yields cycloheptenones.33 Similarly, benzenethiol adds to the central bond of bicyclo[3.2.0]heptan-6-ones in the presence of zinc(II) chloride and hydrochloric acid under anhydrous conditions to form 3-(phenylsulfanyl)cycloheptanones.34... 

Other examples include the intramolecular radical cyclization of 3-bromoaIkyl-2(3fl)-oxazolones 192 and 196 with tributyltin hydride/azobisisobutyronitrile to give the pyrrolooxazolidinones 194,198, and 199. The 2,5-disubstituted pyrrolidine derivatives 195 are produced enantioselectively (Fig. 5.49). 

Intramolecular cyclization of unsaturated acyl chlorides. Tributyltin hydride reduces acyl chlorides to aldehydes by a free-radical chain reaction involving an acyl radical (I, 1193). Cekovic10 now finds that treatment of acyl chlorides with a double bond in the S- or 6-position with tributyltin hydride (azobisisobutyronitrile initiation) gives cyclohexanone derivatives. Thus 5-hexenoyl chloride (1) is converted into cyclohexanone (2), and citronelloyl chloride (3) is converted into menthone (4). 

Radical cyclization of the indole thioesters 107 and 110 with tributyltin hydride and 2,2 -azobisisobutyronitrile (AIBN) gives a mixture of products in each case the 6-< Wo-cyclization product (the indolonaphthyridine, 109 or 112) and the 5-f vv-cyclisation product (the spiro compound 108 or 111) are obtained in approximately equal yield (Equations 22 and 23) <20040L759>. 

A novel homolytic substitution yielded 2-(tributylstannyl)benzothiazole [35]. Thus, 2-(alkylsulfonyl)benzothiazole 49 was allowed to react with 2 equivalents of tributyltin hydride in the presence of catalytic azobisisobutyronitrile (AIBN) in refluxing benzene, affording 2-(tributylstannyl)benzothiazole along with tributylstannylsulfinate 50. 

The silylated tin compound 199, obtained from tributyltin hydride and N-bis(trimethylsilyl)propargylamine (198) in the presence of a trace of AIBN (2,2/-azobisisobutyronitrile), is a versatile reagent for the preparation of allylic amines. Treatment with aryl bromides ArBr (Ar = Ph, 4-MeOCgH4, 4-O2NC6H4 etc.) under Pd(PPh3)4 catalysis yields the silylated amines 200, which are hydrolysed by acids to the free amines 201. 199 is converted into the lithium compound 202, which is transformed into 203 by aqueous ammonium chloride and into 204 by the action of alkyl halides RX (R = Me, Et or allyl) (equation 76)204. 

A general method for the generation of aminyl radicals is by treatment of sulphenamides 340, prepared from secondary amines and A-benzenesulphenylphthalimide, with tributyltin hydride in the presence of AIBN (2,2/-azobisisobutyronitrile). The cyclopropyl derivative... 

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... 

Propargyl bromide Propyne, 3-bromo- (8) 1-Propyne, 3-bromo- (9) (106-96-7) Tributyltin hydride Stannane, tributyl- (8,9) (688-73-3) Azobisisobutyronitrile Propionitrile, 2,2 -azobis[2-methyl- (8) Propanenitrile, 2,2 -azobis[2-methyl- (9) (78-67-1)... 

Treatment of the tricyclic compound 133 with tributyltin hydride and 2,2 -azobisisobutyronitrile (AIBN) produces a radical which cyclizes to give 134 creating a new quaternary center (Equation 35) <2002JA2080>. 

Representative examples are listed in Table 11. Further examples are reported in refs 215 — 217. Similar ring enlargements were found for l-(3-halopropyl)-2-methylenecyclobutanes under the same reaction conditions.218 Thus, 4 is converted to 5 in refluxing benzene after slow addition of tributyltin hydride and catalytic amounts of 2,2 -azobisisobutyronitrile over a period of several hours. Further examples of this reaction are given in ref 218. 

Halobutyl)cyclobutanones form cyclooctanones when they are reduced with tributyltin hydride in the presence of 2,2 -azobisisobutyronitrile.3,5 216, 217 Iodides usually give better yields than bromides. It is essential to add the tin hydride reagent slowly over a period of several hours, to keep its concentration low and thus avoid side reactions. Examples are the reactions to give l,s 2,3 and 3.217 A further example is found in ref 216. 

Bicyclo[3.2.0]hept-2-en-6-one. A solution of freshly distilled tributyltin hydride (31 g, 0.108 mol) (1) in cyclohexane (30 ml) is placed in a three-necked flask equipped with a reflux condenser, a nitrogen inlet tube and a dropping funnel. The flask is flushed with nitrogen. The solution is refluxed while a solution of 7,7-dichlorobicyclo[3.2.0]hept-2-en-6-one (5.83 g, 0.054 mol) in cyclohexane containing a,a -azobisisobutyronitrile (AIBN) (0.1 g, 0.6 mmol) is gradually added. After completion of the addition the mixture is distilled to give 4.38 g (75%) of bicyclo[3.2.0]hept-2-en-6-one (b.p. 62 °C/20 mmHg), no5... 

Regioselective ring opening of the epoxide in 200 occurs in the presence of bromine and triphenylphosphine to give the bromohydrin 201 (R = Br), which on treatment with azobisisobutyronitrile (AIBN) and tributyltin hydride gives the c o-6-hydroxy-2-azabicyclohexane 201 (R = H) <2001JOC1811>. The 5-substituted derivatives of alcohol 201 (R = Me or Ph) are obtained by treatment of 200 with lithium dimethylcopper or lithium diphenylcopper <20040L1669>. 

Reduction of the 2 -deoxynucleosides 165 bearing a 3 -(benzo-l,3-dithiol-2-yloxy) group with tributyltin hydride in the presence of 2,2 -azobisisobutyronitrile (AIBN) followed by methylation with methyl iodide afforded deoxy-nucleosides 256 in high yields (Equation 20) <2004JME5265>. 

Reductive removal of the halogen atom with either Raney-Ni or with tributyltin hydride in the presence of AIBN (azobisisobutyronitrile) as a free-radical initiator furnishes the halide-free lactone. Halolactonization followed by base-induced anti- im-ination of H-I with DBU (l,8-diazabicyclo[5.4.0]undec-7-ene) produces the unsaturated lactone. 

Reduction of 3-acylcyclopropenes using tributyltin hydride and 2,2 -azobisisobutyronitrile gave furans 8 together with ring-opened products 9 and... 

Both products were dechlorinated with tributyltin hydride in refluxing cyclohexant containing a catalytic amount of azobisisobutyronitrile. 

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