Nitriles radical additions

The functionalized dichlorosilane monomers are synthesized generally by radical addition of dichloro-methylsilane to an unsaturated carboxylic acid ester or an unsaturated nitrile. Catalysts used for this purpose are platinum/charcoal (Jl 0,J 1 ), or organic peroxides (T2), but for laboratory syntheses hexachloroplati-nic acid (13,14) proved to be most convenient (scheme 1 a). ... 

As an extension of the known radical additions to isonitriles [87], aryl radical cyclizations to /V-acyl cyanamides provide new access to pyrrolo-quinazolines (Scheme 16) [88]. In a tandem process, the iminyl radical 41 resulting from the 5-exo cyclization onto the nitrile was used for a second cyclization step. In this way, the alkaloid luotonin A (42) was synthesized from cyanamide 43 in a single reaction. 

The photocatalytic radical generation was also used in additions to methyl cyanoformate 143 [240]. The product distribution was dependent on the reaction temperature. At room temperature ot-imino esters 144 were formed in 51-99% yield, while at 90 °C nitriles 145 were isolated in 59-76% yield. At low temperature, the iminyl radical 140C generated by the radical addition, abstracts a hydrogen atom from the substrate to continue a chain reaction, while its fragmentation to the nitrile prevails at high temperature, generating carbon dioxide and a methyl radical 146, which acts as a chain carrier. 

The concept of tungstate-catalyzed radical reactions was recently extended by Albini and coworkers to efficient radical addition reactions to electrophilic alkenes 147 (Fig. 40). Dondi et al. described the photocatalyzed addition of alkyl radicals generated by 310 nm irradiation of 2 mol% decatungstate 139 to ot,(3-unsaturated nitriles [241] or ot,(3-unsaturated ketones [242]. The yields of saturated nitriles 148a were 30-66%, while those of saturated ketones 148b amounted to 21-56% after... 

Giese and coworkers determined on the basis of experimental results obtained by Scheffold et al. [268, 299] that addition reactions of alkyl bromides 249 to a,p-unsaturated nitriles or esters 248 catalyzed by cobalamine 247 are free radical reactions (Fig. 61) [300], This conclusion was based on the similar cis/trans-selectivities in addition reactions of the 4-tert-butylcyclohexyl radical to different electron-poor alkenes 248 using 247 as a catalyst on one hand and classical tributyltin hydride conditions on the other. The kinetics of the radical addition was determined. 

Alkyl radicals are readily generated from azoalkanes by photochem-ically induced elimination of nitrogen. 1-Adamantyl radicals can be obtained in this way by photolysis of azo-1,1 -adamantane in acetonitrile the products are derived principally by hydrogen abstraction from the solvent although radical addition to the nitrile group is also important. The effect of solvent viscosity... 

Related to the intramolecular pinacolic coupling reactions in some respects is a ketone-nitrile reductive coupling process. This process also permits the construction of highly functionalized carbocycles, although the yields are sranewhat reduced owing to the reluctance of nitriles to undergo such radical addition reactions (equation 75). Presumably, simple reduction of the ketone to the alcohol c< npetes with the desired process. 

When oxime benzoates, prepared by benzoylation of dialkyl 1-hydroxyiminophosphonates in the presence of Py, are submitted to the action of tin hydrides under radical conditions, the weakness of the N-0 bond is responsible for the fast formation of the reactive iminyl radical. In the example displayed in Scheme 7.71, the intermediate iminyl radical undergoes cyclization faster than the P-scission to nitrile to give a cyclic aminophosphonale. "- The reaction has also been explored with dialkyl l-benzoyloxyimino-2,2-dimethyl-3,4-pentadienylphosphonate and BujSnH/AIBN in refluxing cyclohexane. In this case, the iminyl radical generated by stannyl radical addition on the benzoyl moiety leads to the sole formation of phosphonylated dihydropyridine in quantitative yield. ... 

An interesting tandem cyelization is used in the synthesis of (-)-a-pipitzol94. The mechanism proceeds via addition of a tin radical to the alkyne, subsequent stereoselective cyelization of the vinyl radical, and addition of the alkyl radical to the nitrile. The addition of tin radicals to alkenes or alkynes is reversible with an unfavorable equilibrium, but in this case the vinyl radical is trapped selectively and irreversibly by cyelization95. 

D. H. Shaw, H. O. Pritchard, Can. J. Chem. 1967, 45, 2749. A free-radical chain mechanism for the isonitrile-nitrile rearrangement in solution was definitely claimed by Riichardt in 1983 M. Meier, C. Riichardt, Tetrahedron Lett. 1983, 24, 4671. Radical addition to isonitriles had been previously claimed by Shono T. Shono, M. Kimura, Y. Ito, K. Nishida, R. Oda, Bull Chem. Soc. Jpn. 1964, 37, 635. 

Radical addition reactions were also recently added to the repertoire of 2-nitroin-dole (21), previously dominated by nucleophilic reactions [17]. Treatment of the indole with activated methylene compounds such as dimethyl malonate, malonitrile and pentane-2,4-dione in a refluxing solution of Mn(0Ac)3-2H20 in acetic acid gave mainly 2-oxo-indolin-ylidenes 22 after an in situ Nef reaction. The expected 3-subsitiuted 2-nitroinole 23, however, was only observed with the methine compounds 3-methylpentane-2,4-dione and 5-oxo-4-propionyUieptane-nitrile. 

Retrosynthetically, a base-catalyzed dimerization of 127 would afford stephacidin B. Avrainvillamide (127) was simplified as vinyl iodide 128 by cleavage of the dihydropyrano [2,3-g]indole-l-oxide moiety and palladium mediated coupling. An aminoacyl radical addition from 129 gave access to 128, while 129 could be derived from cyanide 130 through a hemiaminal formation/dehydration and conjugate addition. Finally, Strecker-like reaction of ketone 131 would fulfill nitrile 130 [55] (Scheme 22). 

The first commercially feasible process for converting acrylic fibers to carbon fibers was developed by Walt, Phillips, and Johnson of the Royal Aircraft Establishment (RAE) in collaboration with the acrylic fiber producer, Courtaulds [621]. In the RAE process, the acrylic precursor is converted to carbon fiber in a two-step process [622]. Preoxidation or filament stabilization is carried out in the first stage. The precursor is heated in an oxygen atmosphere under tension at a temperature of approximately 200 250°C, well below its carbonizing temperature (approximately 800°C). At this temperature, the nitrile groups react with each other via a free radical addition process leading to the so-called ladder structure shown in reaction 12.34 [609,621 625]. 

The types of compounds that can be polymerized readily by the radical-chain mechanism are the same types that easily undergo free-radical addition reactions. Alkenes with aryl, ester, nitrile, or halide substituent groups that can stabilize the intermediate radical are most susceptible to radical polymerization. Terminal alkenes are generally more reactive toward radical-chain polymerization than more highly substituted isomers. The dominant mode of addition in radical-chain polymerization is head-to-tail. The reason for this orientation is that each successive addition of monomer takes place in such a way that the most stable possible radical intermediate is formed. For example, the addition to styrene occurs to give the phenyl-substituted radical to acrylonitrile, to give the cyano-substituted radical ... 

The [Ir(ppy)2bpy] complex photo-catalyses inter- and intramolecular C-H functionalisation reactions of tertiary amines under the visible light irradiation. Oxygen behaves as a chemical switch, triggering different reaction pathways and leading to different products from the same starting material. In anaerobic conditions, the intermolecular addition of iV,iV-dimethyl-anilines to electron-deficient alkenes yields y-amino nitriles. Aerobic conditions, on the other hand, favour a radical addition/ cyclisation reaction, leading to tetrahydroquinoline derivatives. The intramolecular version of the radical addition produces unexpectedly indole-3-carboxaldehyde derivatives. ... 

Furthermore, iminyl radicals have been used in intramolecular homolytic aromatic substitutions. The iminyl radicals can be generated in situ by C-radical addition onto nitriles [55] or they may be generated directly from the corresponding oximes [56] and hydrazones [57]. 

In the reaction of [Co(NH3)5(NCCH2R)] + ions (R = Ph or CH==CHa) with base, deprotonation of the a-CH2 group is followed by rapid intramolecular oxidation to give nitrile radicals which dimerize. Reduction of co-ordinated nitriles with [BH4] ion and Michael additions of carbanions and phosphate to co-ordinated acrylonitrile occur more than 10 times faster than the corresponding reactions of the un-co-ordinated nitriles. Scheme 6 is proposed to account for the formation of (12) from the reaction between [Co(NH3)5(NCMe)] + and CN ions. ... 

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