Enantiopure secondary alcohols are fundamental high-value synthetic building blocks.One of the most attractive ways to get access to this compound class is the catalytic hydroboration. We describe an ew concept for this reaction type that allowed for exceptional catalytic turnover numbers (up to 15 400), which were increased by around 1.5-3 orders of magnitude compared to the most active catalysts previously reported. In our concept an aprotic ammonium halide moiety cooperates with an oxophilic Lewis acid within the same catalyst molecule.C ontrol experiments reveal that both catalytic centers are essential for the observed activity.Kinetic, spectroscopic and computational studies show that the hydride transfer is rate limiting and proceeds via ac oncerted mechanism, in whichh ydride at Boron is continuously displaced by iodide,r eminiscent to an S N 2r eaction. The catalyst, whichi s accessible in high yields in few steps,w as found to be stable during catalysis,r eadily recyclable and could be reused 10 times still efficiently working.

2H-Azirines are synthetically versatile, highly strained, three-membered heterocycles containing an imino double bond. We report their efficient Ru-catalyzed synthesis using low catalyst loadings under neutral conditions from isoxazolinone substrates, which are readily accessible from β-ketoesters. The azirines were shown to be efficient precursors for functionalized pyridine, indole, dihydropyrrole, and pyrrolidine heterocycles.

α-Amino acids are of fundamental importance for life. Both natural and artificial α-amino acids also play a crucial role for pharmaceutical purposes. The catalytic asymmetric Strecker reaction still provides one of the most attractive strategies to prepare scalemic α-amino acids. Here we disclose a new concept for Strecker reactions, in which an achiral Brønsted base cooperates with a Lewis acid and an aprotic ammonium salt, which are both arranged in the same chiral catalyst entity. The described method could successfully address various longstanding practical issues of this reaction type. The major practical advantages are that (1) the N-protecting group is readily removable, (2) acetone cyanohydrin is attractive as cyanation reagent in terms of atom economy and cost efficiency, (3) an excess of the cyanation reagent is not necessary, (4) the new method does not require additives and (5) is performed at ambient temperature.

We apply microkinetic modeling in homogeneous catalysis and show how it can be used to reveal important details of a complex mechanism and how this can lead to a direct comparison between theory and experiment. While regularly used in heterogeneous catalysis, its applications to organic chemistry or homogeneous catalysis are still comparatively scarce. This approach is exemplarily applied to the mechanism of the asymmetric hydroboration of acetophenone with a highly active cooperative Lewis acid−ammonium salt catalyst. In combination with density functional theory, it is a gateway to shed light into important mechanistic details. In our study, it reveals that the counterion of the ammonium salt of the catalyst facilitates the hydride transfer step of the cycle. Chloride replacing iodide speeds up the main reaction but simultaneously has the same effect on a side reaction that consumes the product. This observation is confirmed by experimental measurements of both the main catalytic cycle and the side reaction. A sensitivity analysis showed that the transition from the product complex to the hydride transfer is ratelimiting and that it determines the enantioselectivity. Based on this insight, an enantioselective kinetic model was applied, from which the difference of the Gibbs free energy barriers of the two pathways forming the two enantiomers can be extracted. The barriers are in fairly good agreement with the ones calculated by DFT, which reveal that the asymmetric backbone interacts with the reactant sterically to favor asymmetric product formation.

Enantiopure secondary alcohols are fundamental high-value synthetic building blocks.One of the most attractive ways to get access to this compound class is the catalytic hydroboration. We describe an ew concept for this reaction type that allowed for exceptional catalytic turnover numbers (up to 15 400), which were increased by around 1.5-3 orders of magnitude compared to the most active catalysts previously reported. In our concept an aprotic ammonium halide moiety cooperates with an oxophilic Lewis acid within the same catalyst molecule.C ontrol experiments reveal that both catalytic centers are essential for the observed activity.Kinetic, spectroscopic and computational studies show that the hydride transfer is rate limiting and proceeds via ac oncerted mechanism, in whichh ydride at Boron is continuously displaced by iodide,r eminiscent to an S N 2r eaction. The catalyst, whichi s accessible in high yields in few steps,w as found to be stable during catalysis,r eadily recyclable and could be reused 10 times still efficiently working.