Abstract
Although a plethora of synthetic procedures mediated by KF-loaded aluminas is available in the literature, there is almost no data concerning the influence of parameters such as alumina modification or KF-loading on experimental results. Hence, the Pd-catalyzed, solvent-free Suzuki–Miyaura reaction was chosen as model reaction to investigate the effect of the above mentioned parameters on the results of coupling reactions. The results from ball milling experiments led to the conclusion that self-prepared and commercially available KF–Al2O3 differ in water content. The higher the residual water content, the higher are the product yields.
Highlights
Over the last two decades, a major trend in the field of organic chemistry has been evident: environmentally friendly processes using safer reagents, generating fewer side products and requiring less use of solvents are in vogue [1,2]
Incorporation of KF–Al2O3 as a basic component in organic synthesis is a wide research field [18,19,20,21,22,23,24,25,26,27,28,29]. The application of this reagent is rather problematic, as different reaction protocols for the synthesis of reagents have been published (Table 1) [21,30,31,32,33,34], which differ in the type of alumina used for synthesis and KF-loading
Compared to the original published procedure for the Suzuki–Miyaura reaction [36] or the protocols featured by Mack and Frejd and their coworkers for Sonogashira [54] and Heck–Jeffery couplings applying ball milling conditions [55,56], respectively, the reaction times were substantially reduced from several hours to a few minutes following the present reaction protocol
Summary
Over the last two decades, a major trend in the field of organic chemistry has been evident: environmentally friendly processes using safer reagents, generating fewer side products and requiring less use of solvents are in vogue [1,2]. The as-prepared solid reagent systems (SRS) were applied in solvent-free Pd-catalyzed Suzuki–Miyaura crosscoupling reactions of aryl bromides with phenylboronic acid, and the performances of the individual SRS were compared [33, 34,36,37,38,39,40,41,42]. Scheme 1: Suzuki–Miyaura reaction of phenylboronic acid (1) with aryl bromides 2 yielding substituted biaryls 3 under ball milling conditions (palladium-catalyzed and SRS-assisted).
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