Due to their important roles in medicine and asymmetric metal catalysis, the formation of Betti bases has attracted wide interest in organic chemical community. Traditional multicomponent reaction methods for synthesizing Betti bases normally require long reaction times under harsh conditions (high temperature, microwave or ultrasonic irradiation, etc.) in the presence of various catalysts. In this study, we developed a mild, highly efficient and environmentally friendly method to synthesize Betti bases without the use of any catalysts in microdroplets. The Betti reaction was accelerated by 6.53×103 in microdroplets by comparing the measured rate constant in bulk. Fifteen Betti bases were synthesized by the microdroplet method using a variety of aldehydes, naphthols and amines with 68–98 % yields at a scaled‐up amount of 1.9 g h−1. Overall it is an attractive alternative to classic organic synthesis for the construction of Betti bases and derivatives.
Due to their important roles in medicine, the product of the Petasis reaction has attracted extensive interest in pharmaceutical, medical and chemical communities. Traditional three‐component Petasis methods normally use various catalysts under harsh conditions (high temperature, microwave, etc.) for long reaction times. In this study, we developed a green and highly efficient microdroplet method for accelerating the Petasis reaction, which obtain good yields without the need of any catalysts under mild reaction conditions. The Petasis reaction in microdroplets was suitable for a variety of salicylaldehydes, arylboronic acids and amines. The Petasis reaction in microdroplets was accelerated by approximately 4 orders of magnitude by comparing the measured rate constants in bulk. Further, a scaled‐up amount of 0.8 g h−1 was achieved for the Petasis reaction in microdroplets. This study supplies not only a high‐efficiency and environment‐friendly methodology to constructing aryl amines in organic community but also a useful derivatization strategy for highly sensitive mass spectrometric detection of arylboronic acids and aryl aldehydes.
α-Acyloxy carboxamides are important multifunctional natural products that show bioactive and pharmacological activities. Traditional three-component Passerini reactions among isocyanates, aldehydes/ketones, and carboxylic acids for affording α-acyloxy carboxamides suffer from several drawbacks such as long reaction time, high reaction temperature, special reaction devices, etc. Herein, we developed a high-efficiency microdroplet method for accelerating the Passerini reactions by 3 orders of magnitude by comparing with the rate constants in bulk, achieving high-yield and gram-scale (scaling up to 1.91 g for 1 h collection) synthesis of αacyloxy carboxamides at near room temperature. The Passerini microdroplet method shows a wide scope for a variety of benzoic acids, aryl aldehydes, and isocyanates. Moreover, the Passerini reaction was poorly conducted in aqueous microdroplets but well accelerated in acetonitrile microdroplets with at least 230 times efficiency than on-water Passerini reactions. All results proved it an attractive alternative to classic organic synthesis for the construction of α-acyloxy carboxamides and derivatives.
The cover feature image illustrates two mail devices, drones (representing sprayed microdroplets) and in‐person (representing bulk phase), to deliver a letter (representing the Petasis reaction involving aldehydes, arylboronic acids and amines) in sharply different efficiencies. This study supplies not only a mild, efficient and environmentally friendly methodology to constructing aryl amines in organic community but also a useful derivatization strategy for highly sensitive mass spectrometric detection of arylboronic acids and aryl aldehydes. More information can be found in the Research Article by Heyong Cheng, Jiannan Sun, and co‐workers.
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