The reaction coordinates of an archetypical set of 5-exo cyclizations of C-, N- and O-centred radicals were investigated by computational methods. G4 theory, and DFT with the um062x functional, were able to rationalise counterintuitive factors such as the 'normal' order of rate constants being: N-centred < C-centred < O-centred radicals. The access angle between the radical centre and the double bond was identified as a key factor. Examination of its evolution during ring closure implied that rigidity at the N-ends of the chains, and the consequent extra energy needed to attain chair-like transition states, might be the reason for slow aminyl cyclizations. A novel linear correlation between cyclization activation energies and the access angles was discovered. The preference for cis-1,2-disubstituted product formation was also accounted for in terms of interaction between the hyperconjugatively delocalized SOMO and the alkene π* orbital.
Download full-text PDF |
Source |
|---|---|
| http://dx.doi.org/10.1039/c4ob01419g | DOI Listing |
Publication Analysis
Top Keywords
Similar Publications
Organophotocatalytic Generation of N- and O-Centred Radicals Enables Aerobic Oxyamination and Dioxygenation of Alkenes.
Chemistry
September 2016
CCNU-uOttawa Joint Research Center, Key Laboratory of Pesticide & Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University (CCNU), 152 Luoyu Road, Wuhan, Hubei, 430079, P. R. China.
A cooperative TEMPO and photoredox catalytic strategy was applied for the first time to the direct conversion of N-H and O-H bonds into N- and O-centred radicals, enabling a general and selective oxidative radical oxyamination and dioxygenation of various β,γ-unsaturated hydrazones and oximes. In the reaction, O2 was employed not only as a terminal oxidant but also as the oxygen source. This protocol provided efficient access to the synthesis of various synthetically and biologically important pyrazoline, pyridazine and isoxazoline derivatives under metal-free and mild reaction conditions.
View Article and Find Full Text PDFFunctionalised Oximes: Emergent Precursors for Carbon-, Nitrogen- and Oxygen-Centred Radicals.
Molecules
January 2016
EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, UK.
Oxime derivatives are easily made, are non-hazardous and have long shelf lives. They contain weak N-O bonds that undergo homolytic scission, on appropriate thermal or photochemical stimulus, to initially release a pair of N- and O-centred radicals. This article reviews the use of these precursors for studying the structures, reactions and kinetics of the released radicals.
View Article and Find Full Text PDFA novel transition metal free [bis-(trifluoroacetoxy)iodo]benzene (PIFA) mediated oxidative ipso nitration of organoboronic acids.
Org Biomol Chem
May 2015
Department of Chemistry, Indian Institute of Technology, Ropar (IIT Ropar), Nangal Road, Rupnagar, Punjab 140001, India.
A mild, convenient and transition metal free methodology for oxidative ipso nitration of diversely functionalized organoboronic acids, including heteroaryl- and alkylboronic acids, has been developed at ambient temperature using a combination of [bis-(trifluoroacetoxy)]iodobenzene (PIFA) - N-bromosuccinimide (NBS) and sodium nitrite as the nitro source. It is anticipated that the reaction proceeds through in situ generation of NO2 and O-centred organoboronic acid radicals followed by the formation of an O-N bond via combination of the said radicals. Finally transfer of the NO2 group to the aryl moiety occurs through 1,3-aryl migration to provide the nitroarenes.
View Article and Find Full Text PDFThe importance of chain conformational mobility during 5-exo-cyclizations of C-, N- and O-centred radicals.
Org Biomol Chem
October 2014
University of St. Andrews, EaStCHEM School of Chemistry, St. Andrews, Fife, KY16 9ST, UK.
The reaction coordinates of an archetypical set of 5-exo cyclizations of C-, N- and O-centred radicals were investigated by computational methods. G4 theory, and DFT with the um062x functional, were able to rationalise counterintuitive factors such as the 'normal' order of rate constants being: N-centred < C-centred < O-centred radicals. The access angle between the radical centre and the double bond was identified as a key factor.
View Article and Find Full Text PDFCobalt complexes bearing scorpionate ligands: synthesis, characterization, cytotoxicity and DNA cleavage.
Dalton Trans
November 2012
Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
A number of novel, water-stable redox-active cobalt complexes of the C-functionalized tripodal ligands tris(pyrazolyl)methane XC(pz)(3) (X = HOCH(2), CH(2)OCH(2)Py or CH(2)OSO(2)Me) are reported along with their effects on DNA. The compounds were isolated as air-stable solids and fully characterized by IR and FIR spectroscopies, ESI-MS(+/-), cyclic voltammetry, controlled potential electrolysis, elemental analysis and, in a number of cases, also by single-crystal X-ray diffraction. They showed moderate cytotoxicity in vitro towards HCT116 colorectal carcinoma and HepG2 hepatocellular carcinoma human cancer cell lines.
View Article and Find Full Text PDFWant AI Summaries of new PubMed Abstracts delivered to your In-box?
Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!