Homolytic dissociation of 1-substituted cyclohexa-2,5-diene-1-carboxylic acids: an EPR spectroscopic study of chain propagation†

Silylated Cyclohexadienes as New Radical Chain Reducing Reagents: Preparative and Mechanistic Aspects

“…Thus, the somewhat smaller k H value for 10 (which lacks the methoxy substituents) in comparison with 4 , is in accord with expectation. Comparison with analogous data for the 1-ethylcyclohexa-2,5-diene-1-carboxylic acid,4e (Table ) shows an even smaller k H value for this material, again suggesting that the 2,6-methoxy substituents significantly enhance the H-donation ability of 4 . This factor may contribute considerably to the efficiency of 4 as mediator of the chain reactions.…”

“…One of us (JCW) has successfully used functionalized cyclohexadienes in radical chain reactions . For example, 1-carbamoylcyclohexa-2,5-dienes are effective sources of aminoacyl radicals that ring close to yield β- and γ-lactams. 4d,f On the basis of these results, the German group has introduced silylated 1,4-cyclohexadienes of type 1 as new, readily prepared radical chain reducing reagents . The cyclohexadiene bis-allylic CH 2 -moiety acts as the H-donor in these chain reactions.…”

A kinetic EPR study of the dissociation of 1-carbamoyl-1-methylcyclohexa-2,5-dienyl radicals: release of aminoacyl radicals and their cyclisationElectronic supplementary information (ESI) available: Selected EPR spectra, measured radical concentrations and the corresponding rate constants at each temperature for each cyclohexadienyl. AM1 computed heats of formation and selected geometric parameters for a series of cyclohexadienyl radicals and dissociation products. UB3LYP computed energies for model aminoa

“…as long as the longest computed for C(1)-alkyl in the analogous 1-alkylcyclohexa-2,5-dienyl-1-carboxylic acid radicals. 9 The computed enthalpies of reaction (∆H o ) for both modes of dissociation are listed in Table 4.…”

“…EPR spectroscopy has proved effective as a method for characterising the intermediates and measuring key rate constants of reactions of cyclohexadienyl derivatives. 9 This paper † Electronic supplementary information (ESI) available: Selected EPR spectra, measured radical concentrations and the corresponding rate constants at each temperature for each cyclohexadienyl. AM1 computed heats of formation and selected geometric parameters for a series of cyclohexadienyl radicals and dissociation products.…”

Approach to 3-Aminoindolin-2-ones via Oxime Ether Functionalized Carbamoylcyclohexadienes

“…Functionalized cyclohexadienes combine within one compound the ability to release a desired radical and hydrogen donor capability. We have successfully used them in radical chain reactions, 5a-e and Studer et al have introduced silylated 1,4-cyclohexadienes that efficiently release silyl radicals for use in conjunction with an organic halide precursor. 6a,b 1-Carbamoyl-2,5-cyclohexadienes release carbamoyl radicals (aminoacyl radicals), suitably unsaturated examples of which ring close to afford β- or γ-lactams in moderate yields. 7a-c…”