Azobisisobutyronitrile synthesis

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. 

Several radical approaches have been also used for the synthesis of 3-oxo-perhydro derivatives based on the use of trimethylstannyl chloride or tributylstannyl chloride activation in presence of 2,2 -azobisisobutyronitrile (AIBN) <1996JOC5418, 2000TL5915>. Photochemical strategies were applied to the formation of 3-oxo perhydro intermediates <1998J(P1)3577>. Compounds 348 and 349 were isolated as a 1 1 mixture after photolysis of 347 using a high-pressure mercury lamp in quartz tubes at room temperature in the presence of cr-trifluoro-acetophenone and KF (Equation 61) <2002TL7777>. 

Scheme 18.11 Synthesis of (R)-(—)-tricosa-9,l 0-diene (27a) from chiral propargylic alcohol 28 (AlBN = azobisisobutyronitrile) [37].

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 tin hydride method suffers from one major disadvantage, namely the efficiency of the reagent as a hydrogen atom donor. For successful synthesis, alkenes have to be reactive enough, otherwise direct reduction of the starting precursor becomes a considerable side reaction. In practice, the yields are increased by slow addition of a solution of tin hydride and a radical initiator into the reaction mixture containing an excess of alkene. However, a delicate balance must be maintained. If a large excess of olefin is used, polymerization can compete. 2,2-Azobisisobutyronitrile is the most commonly employed initiator, with a half-life time for unimolecular scission of 1 h at 80°C. 

Stereoselective radical cyclization (Equation 20) initiated by Bu3SnH/AIBN or Bu3SnH/Et3B is suggested as a method for the synthesis of O-linked oxepane ring systems (AIBN = 2,2 -azobisisobutyronitrile) <1998TL2783>. 

The second synthesis [6], based on radical chemistry to achieve the crucial Caryi-Cgryi bond, required as the starting material the 2-bromobenzyl-2 -aminophenyl ether (11) (Scheme 2). It was secured by alkylation of o-nitrophenol with 2-bromo-4,5-methylenedioxybenzyl chloride, followed by catalytic reduction of the resulting nitropheny ether. 11 when subjected to the action of tri-n-butyltinhydride in the presence of 2,2 -azobisisobutyronitrile furnished a... 

Pancratistatln. The first total synthesis of ( )-pancratistatin (94) (Scheme 14), the structurally most complex of narciclasine alkaloids, was achieved by Danishefsky [27]. The requisite starting material, the substituted benzaldehyde 95 prepared from pyrogallol in six steps in 18% overall yield, was converted via the homoallylic alcohol 96 into the diene 97. Reaction of 97 with 2-nitrovinylsulphone yielded the cycloadduct 98, which on treatment with tributyltinhydride and 2,2 -azobisisobutyronitrile furnished the cyclohexadiene 99. Whilst the cyclisation of the silylether 99 or the derived phenol, under the influence of iodine, could not be accomplished, the more nucleophilic stannylether did participate in the desired ring closure and provided via the iminium salt, the iodolactone 100 on aqueous work-up. 

SCHEME 3.25 Synthesis of a 2-deoxyglycoside using the glycal approach. AIBN, azobisisobutyronitrile. 

SCHEME 14.21 Synthesis of the O-linked oligosaccharide of BclA by Seeberger and coworkers. AIBN, azobisisobutyronitrile TCA, trichloroacetyl. 

The synthesis of poly(butyl acrylate) in the presence of cysteine was carried out using THF, ethyl alcohol, and water where the molar ratio of butyl acrylate monomer/ cysteine/azobisisobutyronitrile was 1000 30 1, respectively. The mixture was then refluxed for 6 hours at 65°C while under constant stirring. After cooling the cysteine-modified product consisted of a white precipitate dispersed within poly(butyl acrylate). The precipitate was isolated from the polymer by dissolving the poly(butyl acrylate) in THF and filtering. 

Synthesis was carried out of the copolymers of 4-vinylpyridine (4VP), styrene (St) and divinylbenzene (DVB) with varied compositions, P(4VP-St-DVB), by suspensionpolymerisationusing 2,2 -azobisisobutyronitrile (AIBN) as an initiator. Preparation of the insoluble (crosslinked) pyridinium-type polymers in benzyl-pyridinium bromide form, which possess various macromolecular chain compositions, was performed by the reaction of eachP(4VP-St-DVB) with benzyl bromide (BzBr), respectively. By using different halohydrocarbon RX in the quatemisation of P(4VP-St-DVB), the insoluble pyridinium-type polymers with various pyridinium group stractures were obtained. FTIR was nsed to identify the stractures of P(4VP-St-DVB) and its quatemised product Q-P(4VP-St-DVB). The 4VP content in each copolymer P(4VP-St-DVB) was measured by non-aqueous titration and the pyridinium group content (Cq) in each Q-P(4 VP-St-DVB) sample was determined by means of the back titration manner in argentometiy and/or the elemental analysis method, respectively. Also, the particle structure... 

The second Matsuo synthesis (233) was initiated with methyl 3-(2,2-dimethoxyethyl)-4-methyl-4-pentenoate (357) prepared (234) from carvone (239). Hydrolysis with lithium hydroxide followed by iodolactonization (I2-KI-NaHC03) and reduction with tri-n-butyl tin hydride in the presence of azobisisobutyronitrile in benzene under reflux afforded 358. The carbo-methoxy group was introduced with methyl chloroformate and LDA in quantitative yield, and reductive animation of 359 with methylamine and sodium cyanoborohydride gave the lactone 360. Heating of 360 with 10% Pd/C in decalin gave cerpegin (118) in 81% yield (Scheme 42) (233). 

Azo compounds are widely used as radical initiators in organic synthesis [1], AIBN (2,2 -azobisisobutyronitrile) is the most commonly used initiator because of its high decomposition ability and stability. Azo compounds are decomposed by heat to the corresponding alkyl radicals and nitrogen [1]. As previously described, it is known that they undergo decomposition via the cis form by absorbing light [3]. 

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