Department of Chemistry, Indian Institute of Science Education and Research Bhopal (IISER), Bhopal, Madhya Pradesh 462 023, India.
J Org Chem. 2012 Nov 2;77(21):9541-52. doi: 10.1021/jo301486c. Epub 2012 Oct 18.
Isoselenazolones were synthesized by a copper-catalyzed Se-N bond forming reaction between 2-halobenzamides and selenium powder. The catalytic activity of the various isoselenazolones was studied in the bromolactonization of pent-4-enoic acid. Isoselenazolone 9 was studied as a catalyst in several reactions: the bromolactonization of a series of alkenoic acids with bromine or N-bromosuccinimide (NBS) in the presence of potassium carbonate as base, the bromoesterification of a series of alkenes using NBS and a variety of carboxylic acids, and the oxidation of secondary alcohols to ketones using bromine as an oxidizing reagent. Mechanistic details of the isoselenazolone-catalyzed bromination reaction were revealed by (77)Se NMR spectroscopic and ES-MS studies. The oxidative addition of bromine to the isoselenazolone gives the isoselenazolone(IV) dibromide, which could be responsible for the activation of bromine under the reaction conditions. Steric effects from an N-phenylethyl group on the amide of the isoselenazolone and electron-withdrawing fluoro substituents on the benzo fused-ring of the isoselenazolone appear to enhance the stability of the isoselenazolone as a catalyst for the bromination reaction.
异硒唑酮是通过 2-卤代苯甲酰胺和硒粉之间的铜催化 Se-N 键形成反应合成的。研究了各种异硒唑酮在戊-4-烯酸的溴内酯化反应中的催化活性。异硒唑酮 9 被用作几种反应的催化剂：在碳酸钾作为碱存在下，用溴或 N-溴代丁二酰亚胺 (NBS) 对一系列烯酸进行溴内酯化，用 NBS 和各种羧酸对一系列烯烃进行溴酯化，以及用溴作为氧化剂将仲醇氧化为酮。通过 (77)Se NMR 光谱和 ES-MS 研究揭示了异硒唑酮催化溴化反应的机理细节。溴对异硒唑酮的氧化加成生成异硒唑酮(IV)二溴化物，这可能是在反应条件下溴活化的原因。酰胺上的 N-苯乙基基团的空间位阻和异硒唑酮的苯并稠合环上的吸电子氟取代基似乎增强了异硒唑酮作为溴化反应催化剂的稳定性。
