Some Items of Interest to Process R&D Chemists and Engineers

Abstract

■ COPPER-CATALYZED SYNTHESIS OF HINDERED ANILINES Lalic and co-workers have recently described an improvement of the reaction conditions for their previously published electrophilic amination of (hetero)aryl boronic ester (Chem. Commun. 2015, 51, 11048). The main features of their newly developed method are the replacement of lithium tert-butoxide by cesium fluoride and of the hard to prepare and air-sensitive Cu(Ot-Bu) 4 catalyst by copper(I) triflate benzene complex. These changes allow the reaction to take place in ethereal solvents (THF, 2-MeTHF, or dioxane) instead of iso-octane and tolerates a wide range of functionalities in the (hetero)-aromatic coupling partner such as aldehyde or free alcohol. Moreover, the scope of the reaction, which was limited to the synthesis of tertiary anilines, can be extended to secondary anilines by performing a slow addition of the N-alkyl-O-benzoyl hydroxylamine electrophiles over 3 h. Interestingly, all halogen substituents remain unaffected under the developed conditions. A catalytic cycle for the reaction has been proposed in which the rate-limiting step would be the formation of a copper fluoride complex from the catalyst resting state. ■ ANILINE-CATALYZED HALOGENATION Selective halogenation is a fundamental reaction of the organic chemist toolkit, and a host of different reactants has been developed to accommodate each substrate class, one of the latest being Baran's Palau'Chlor. By using anilines as catalyst, Yamamoto and Samanta from Japan have recently discovered that the reactivity and selectivity profiles of N-halosuccinimides can be greatly improved (Chem. Eur. J. 2015, 21, 11976). Identification of catalyst deactivation pathways allowed the authors to develop reaction conditions for chlorination, bromination, and iodination. These conditions differ by the amount (1−10 mol %) and nature of the catalyst (2,4,6-trimethylaniline or 2,4,6-trifluoroaniline) and by the temper-ature at which the reaction is run (room temperature or −40 °C). A number of electron rich heteroaromatic and aromatic compounds are selectively and effectively halogenated with the influence of electronic and steric factors leading, in certain cases, to different isomers being predominant depending on the halogen atom introduced. Direct comparison with the perform-ance of NCS alone and Palau'Chlor is also provided for selected examples.