A free radical chain mechanism for the isonitrile - nitrile rearrangement in solution and its inhibition

Copper-catalyzed alkylarylation of activated alkenes using isocyanides as the alkyl source: an efficient radical access to 3,3-dialkylated oxindoles

A novel copper-catalyzed oxidative cyclization of N-arylacrylamides for the synthesis of 3,3-dialkylated oxindoles is described using isocyanides as alkyl radical precursors.

3/2-Order Chain Kinetics Involving a Postulated Dicationic Intermediate in the Isomerization of a P−Isocyano to a P−Cyano Azaphosphatrane Monocation

Kinetic evidence suggests the possibility of a dicationic intermediate in the title reaction. Thus the linkage isomerization reaction, PNC+ = PCN+, is described by the rate law, nu = 3/2k[PNC+]3/2, which can be interpreted by a chain mechanism with the propagation reaction PNC+ + P2+ --> P2+ + PCN+. Such propagation is unusual in that the intermediate regenerates itself in this single step rather than forming a different intermediate for a second propagation step. Cyanide ions inhibit the rate because they participate in the termination step, P2+ + CN- --> PCN+. The rate constant in CD3CN at 100 degrees C is 3/2k = 7.2 +/- 0.6 x 10-5 L1/2 mol-1/2 s-1; 3/2k represents the composite (kinit/kterm)1/2 kprop. When the reaction is carried out in the presence of PBr+, however, the reaction becomes much faster and is described by the rate law, nu = kBr[PBr+][PNC+]; because [PBr+] remains at constant concentration, the time-course experiments follow first-order kinetics.

Synthetic and theoretical studies on group-transfer imidoylation of organotellurium compounds. remarkable reactivity of isonitriles in comparison with carbon monoxide in radical-mediated reactions

Imidoylation of organotellurium compounds with isonitriles has been investigated in conjunction with the radical-mediated C1 homologation reaction by using CO and isonitriles. Carbon-centered radicals generated photochemically or thermally from organotellurium compounds react with isonitriles in a group-transfer manner to give the corresponding imidoylated products. Organotellurium compounds have been found to serve as effective precursors of a wide variety of stabilized radicals, namely benzyl, alpha-alkoxy, alpha-amino, and acyl radicals, which take part in the imidoylation with high efficiency. The reactions are compatible with various functional groups, and can be carried out in various solvents including environmentally benign water. The reactivity of isonitriles has been compared with that of CO through competition experiments, and the results indicate that isonitriles are superior to CO as radical acceptors in reactions with stabilized radicals. The origin of the differences has been addressed in theoretical studies with density functional theory calculations using the B3LYP hybrid functional. The calculations suggest that both carbonylation and imidoylation proceed with low activation energies, and that there are virtually no differences in the kinetic sense. Instead, it indicates that thermodynamic effects, namely differences in the stability of the acyl and the imidoyl radicals, control the overall course of the reactions.

Radical addition to isonitriles: a route to polyfunctionalized alkenes through a novel three-component radical cascade reaction

The reaction of aromatic disulfides, alkynes, and isonitriles under photolytic conditions affords polyfunctionalized alkenes--beta-arylthio-substituted acrylamides or acrylonitriles--in fair yields through a novel three-component radical cascade reaction. The procedure entails addition of a sulfanyl radical to the alkyne followed by attack of the resulting vinyl radical to the isonitrile. A fast reaction, e.g., scavenging by a nitro derivative or beta-fragmentation, is necessary in order to trap the final imidoyl radical, since addition of vinyl radicals to isonitriles seems to be a reversible process. The stereochemistry of the reaction is discussed, particularly with respect to the stereochemical outcome of related hydrogen abstraction reactions by the same vinyl radicals. The lower or even inverted preference for either geometrical isomer observed in our cases with respect to that encountered in hydrogen abstraction reactions is explained in terms of transition-state interactions and/or isomerization of the final imidoyl radical. The latter possibility is supported by semiempirical calculations, which show that the spin distribution in the imidoyl radical can allow rotation of the adjacent carbon-carbon double bond prior to beta-fragmentation.

alpha-(Arylthio)imidoyl Radicals: [3 + 2] Radical Annulation of Aryl Isothiocyanates with 2-Cyano-Substituted Aryl Radicals

A novel cascade radical reaction is described involving aryl isothiocyanates and 2-cyanoaryl radicals. The mechanism entails the formation of an alpha-(arylthio)imidoyl radical, a 5-exo-dig cyclization onto a cyano group, and a final 6-membered ring closure of an iminyl radical. The competitive 5-membered spiro-cyclization of the iminyl, leading to an isomeric product, was only observed in the case of a disubstituted aryl isothiocyanate. The whole process involves a rare example of [3 + 2] radical annulation and allows the one-pot synthesis of tetracondensed nitrogen heterocycles in good yields.