Cyclization of the 4-cyanobutyl radical

Abstract

. INGOLD. Can. J. Chem. 57,831 (1979). The rate constant for the irreversible cyclization of the 4-cyanobutyl radical to the cyclopentiminyl radical, kcCzN, has been measured from -52 to 12°C by kinetic epr spectroscopy. The temperature dependence of this rate constant can be represented by, log (k,C'N/s-') = (9.9 2 1.0) -(8.6 t l.0)/8 where 8 = 2.3RT kcal/mol. This rearrangement is somewhat slower than the analogous cyclizations of the 5-hexenyl and 5-hexynyl radicals.DAVID GRILLER, PETER SCHMID et KEITH U. INGOLD. Can. J. Chem. 57,831 (1979). On a mesurk les constantes de vitesse de la cyclisation irrtversible du radical cyano-4 butyle en radical cyclopentiminyle, kcCEN, a des tempkratures allant de -52 a 12°C en faisant appel a la spectroscopie rpe. On peut reprtsenter la relation entre la constante de vitesse et la temptrature grlce a l'tquation oh 0 = 2.3RT kcal/mol. Cette transposition est un peu plus lente que les cyclisations analogues des radicaux hexenyle-5 et hexynyle-5.[Traduit par le journal]

Cascade cyclization of 1-(2-yl-3-phenylprop-2-enyl)-6-oxo-1,6-dihydropyridine-2-carbonitrile radical: Mechanistic insights from DFT study

“…Thereby, the regiochemistry of the first step in the cascade radical cyclization becomes apparent, i.e., it should be a carbon-philic cyclization, not a nitrogen-philic cyclization. The favored carbonphilic 5-exo cyclization of carbon-centered radicals onto nitrile group has been frequently observed in previous investigations [42,43,[107][108][109]. The thermodynamical preponderance of the 5-exo cycloadduct 4 relative to the 6-endo cycloadduct 9 mainly comes from the low-strained in-plane structure of the singly occupied molecular orbital (SOMO) of the exocyclic iminyl radical in 4 and the high-lying endocyclic carbon-centered radical in 9.…”

Hydrogen Atom Transfer‐Mediated Cyclisations of Nitriles

“…Yet, despite the use of radical acceptors such as acrylonitrile, the HAT‐initiated radical addition to nitriles has remained unreported. Whilst radical cyclisation onto a C≡N π‐bond is feasible, it is about 50 times slower than its C=C and C≡C variants . This is highlighted by the numerous reported failed attempts to cyclise onto a nitrile group; although in isolated examples, radical cyclisations to nitriles have been achieved utilising tributyltin hydride, titanium and manganese reagents.…”

“…Whilst radical cyclisationo nto aC N pbond is feasible, it is about 50 times slowert han its C=Ca nd CCv ariants. [13] This is highlighted by the numerousr eported failed attempts to cyclise onto an itrile group; [14][15][16] although in isolated examples, radical cyclisations ton itriles have been achieved utilisingt ributyltinh ydride, [17][18][19] titanium [20][21][22] and manganese [23] reagents.…”

Light-Induced Iminyl Radicals: Generation and Synthetic Applications

“…5-Bromovaleronitrile was used to establish the rate constant of cyclization of the 4-cyanobutyl radical to the cyclopentiminyl radical (Griller et al, 1979), as determined by kinetic measurements using electron paramagnetic resonance (EPR) spectroscopy, and this was found to be k With respect to intermolecular reactions, a couple of examples have been reported where photochemically generated radicals add to acetonitrile (Engel et al, 1987;de Lijser & Arnold, 1997). Carbon-centred radicals prefer to add to the carbon of the nitrile to give the iminyl radical (de Lijser & Arnold, 1998), a preference that has been rationalized by a timeresolved infrared study on the photochemistry of O-fluoroformyl-9-fluorenone oxime in acetonitrile solution and by ab initio molecular orbital calculations (Bucher et al, 2006).…”