3263-79-4Relevant articles and documents
Pyrroles as antioxidants: Solvent effects and the nature of the attacking radical on antioxidant activities and mechanisms of pyrroles, dipyrrinones, and bile pigments
MacLean, Patricia D.,Chapman, Erin E.,Dobrowolski, Sarah L.,Thompson, Alison,Barclay, L. Ross C.
, p. 6623 - 6635 (2008)
(Chemical Equation Presented) The absolute rate constants, kinh, and stoichiometric factors, n, of pyrroles, 2-methyl-3-ethylcarboxy-4,5-di-p- methoxyphenylpyrrole, 6, 2,3,4,5-tetraphenylpyrrole,7, and 2,3,4,5-tetra-p- methoxyphenylpyrrole, 8, compared to the phenolic antioxidant, di-tert-butylhydroxyanisole, DBHA, during inhibited oxidation of cumene initiated by AIBN at 30°C gave the relative antioxidant activities (k inh) DBHA > 8 > 7 > 6 and n = 2, whereas in styrene, 8 > DBHA. These results are explained by hydrogen atom transfer, HAT, from the N-H of pyrroles to ROO? radicals. The kinh values in styrene of dimethyl esters of the bile pigments of bilirubin ester (BRDE), of biliverdin ester (BVDE), and of a model compound (dipyrrinone, 1) gave k inh in the order pentamethylhydroxychroman (PMHC) BRDE > 1 > BVDE. These antioxidant activities for BVDE and the model compound, 1, and PMHC dropped dramatically in the presence of methanol due to hydrogen bonding at the pyrrolic N-H group. In contrast the kinh of BRDE increased in methanol. We now show that pyrrolic compounds may react by HAT, proton-coupled electron transfer, PCET, or single electron transfer, SET, depending on their structure, the nature of the solvent, and the attacking radical. Compounds BVDE and 1 react by the HAT or PCET pathway (HAT/PCET) in styrene/chlorobenzene with ROO? and with the DPPH? radical in chlorobenzene according to N-H/N-D kH/kD of 1.6, whereas the DKIE with BRDE was only 1.2 with ROO?. The antioxidant properties of polypyrroles of the BVDE class and model compounds (e.g., 1) are controlled by intramolecular H bonding which stabilizes an intermediate pyrrolic radical in HAT/PCET. According to kinetic polar solvent effects on the monopyrrole, 8, and BRDE, which gave increased rates in methanol, some pyrrolic structures are also susceptible to SET reactions. This conclusion is supported by some calculated ionization potentials. The antioxidant mechanism for BRDE with peroxyl radicals is described by the PCET reaction. Experiments using the 2,6-di-tert-butyl-4- (4′-methoxyphenyl)phenoxyl radical (DBMP?) showed this to be a better radical to monitor HAT activities in stopped-flow kinetics compared to the use of the more popular DPPH? radical.
Base-Mediated Direct Transformation of N-Propargylamines into 2,3,5-Trisubstituted 1 H-Pyrroles
Mishra, Pawan K.,Verma, Shalini,Kumar, Manoj,Verma, Akhilesh K.
, p. 7182 - 7185 (2018/11/25)
An efficient and base-mediated intramolecular cyclization of N-propargylamines for the synthesis of structurally diversified pyrroles in high yield has been described. The developed methodology is broadly applicable and is tolerated by a variety of functional groups. Key intermediates of natural product discoipyrrole C as well as HMG-CoA-reductase inhibitor have been successfully synthesized using developed chemistry. The proposed mechanism was supported by control experiments.
Copper-catalyzed homocoupling of ketoxime carboxylates for synthesis of symmetrical pyrroles
Ran, Longfei,Ren, Zhi-Hui,Wang, Yao-Yu,Guan, Zheng-Hui
supporting information, p. 112 - 115 (2014/01/06)
A novel and efficient copper-catalyzed homocoupling of ketoxime carboxylates has been developed for the synthesis of symmetrical pyrroles. This reaction tolerates a wide range of functional groups and provides a synthetically useful process to synthesize
