Thermolyses of O-Phenyl Oxime Ethers. A New Source of Iminyl Radicals and a New Source of Aryloxyl Radicals

From National Research Council Canada

DOI	Resolve DOI: https://doi.org/10.1021/jo049927y
Author	Search for: Blake, J.A.¹; Search for: Pratt, D.A.; Search for: Lin, S.¹; Search for: Walton, J.C.; Search for: Mulder, P.; Search for: Ingold, K. U.¹
Name affiliation	National Research Council of Canada
Format	Text, Article
Subject	Dissociation; Enthalpy; Free radicals; Reaction kinetics; Synthesis (chemical); Cyclization; Hyperconjugation; Thermolyses; Ethers; ether derivative; imine; iminyl radical; n phenoxybenzimidic acid phenyl ether; o phenyl oxime ether derivative; oxyl radical; phenoxybenzamine; radical; unclassified drug; beta scission; binding competition; calculation; chemical analysis; chemical binding; chemical reaction kinetics; conjugation; cyclization; density functional theory; dissociation; enthalpy; product recovery; reaction analysis; room temperature; synthesis; temperature sensitivity; thermal analysis; thermolysis
Abstract	Six O-phenyl ketoxime ethers, RR′C=NOPh 1-6, with RR′= diaryl, dialkyl, and arylalkyl, together with N-phenoxybenzimidic acid phenyl ether, PhO(Ph)C=NOPh, 7, have been shown to thermolyze at moderate temperatures with "clean" N-O bond homolyses to yield iminyl and phenoxyl radicals, RR′C=N. and PhO.. Since 1-6 can be synthesized at room temperature, these compounds provide a new and potentially useful source of iminyls for syntheses. The iminyl from 7 undergoes a competition between β-scission, to PhCN and PhO., and cyclization to an oxazole. Rate constants, 106 k/s-1, at 90 °C for 1-6 range from 4.2 (RR′ = 9-fluorenyl) to 180 (RR′ = 9-bicyclononanyl), and that for 7 is 0.61. The estimated activation enthalpies for N-O bond scission are in satisfactory agreement with the results of DFT calculations of N-O bond dissociation enthalpies, BDEs, and represent the first thermochemical data for any reaction yielding iminyl radicals. The small range in k (N-O homolyses) is consistent with the known σ structure of these radicals, and the variations in k and N-O BDEs with changes in RR′ are rationalized in terms of iminyl radical stabilization by hyperconjugation: RR′C=N . ↔ R.R′C≡N. Calculated N-H BDEs in the corresponding RR′C= NH are also presented.
Publication date	2004
In	Journal of Organic Chemistry 69, no. 9 (2004): 3112–3120.
Language	English
Peer reviewed	Yes
NPARC number	21276655
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Record identifier	217b530b-6469-4c68-9bab-3af48ea6c0e2
Record created	2015-10-13
Record modified	2020-04-17

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