Efficient scale up of photochemical bromination of conjugated allylic compounds in continuous-flow
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Efficient scale up of photochemical bromination of conjugated allylic compounds in continuous-flow Jiadi Zhou 1,2 & Zhi Chen 3 & Yunfei He 3 & Zhihao Lin 3 & Chaodong Wang 3 & Zhonghui Li 3 & Jianjun Li 1,2,3 Received: 21 July 2020 / Accepted: 10 September 2020 # Akadémiai Kiadó 2020
Abstract A continuous-flow process for the bromination of conjugated allylic compounds with N-bromosuccinimide (NBS) is developed. The reaction was optimized in a self-made continuous-flow photoreactor based on a commercially available household lamp. The productivity of this continuous step attains 70.5 g/h under the optimal conditions. Compared to batch-mode synthesis, the conversion rate and selectivity of this flow-mode was significantly improved. In addition, the reaction time could be significantly reduced from a few hours to a few minutes. Keywords Continuous-flow . Photochemistrys . Conjugated allylic bromination . Scalable productivity
Introduction The traditional benzylic and allylic bromination using NBS in refluxing CCl4 initiated by a radical initiator (benzoyl peroxide or 2,2′-azobis (isobutyronitrile)) has been developed [1–4]. Although NBS is a safer and more friendly brominating agent than Br2, the traditional batch bromination was limited by the use of the ozone-depleting and toxic CCl4 [5, 6]. In the recent years, scientists have made significant efforts in Jiadi Zhou and Zhi Chen contributed equally to this work. Highlights Development of conjugated allylic brominations reaction in continuousflow with high conversion rate, selectivity and productivity. Optimized the process parameters experiments approach. Designed a new type of reaction device. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s41981-020-00116-3) contains supplementary material, which is available to authorized users. * Jianjun Li [email protected] 1
Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, Zhejiang University of Technology, Hangzhou 310014, People’s Republic of China
2
National Engineering Research Center for Process Development of Active Pharmaceutical Ingredients, Zhejiang University of Technology, Hangzhou 310014, People’s Republic of China
3
College of Pharmaceutical Sciences, Zhejiang University of Technology, Hangzhou 310014, People’s Republic of China
developing greener bromination procedures, focusing on replacing dangerous CCl4 with green solvents. Thus, several nonchlorinated solvents have been described, such as ethyl acetate [7], methyl acetate [8], acetonitrile [9], water [10], ionic liquids [11] or even solvent-free conditions [12–14]. In recent years, the combination of continuous-flow and photochemistry have been increasingly applied, which can achieve efficient light irradiation and a repeatable energysaving system [15–19]. In general, the flow-reaction system allows the products to be rapidly transferred from the reactor, which suppress undesired over-reactions [20, 21]. Importantly, by simply stacking the number of rea
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