Herein we report the isolation and characterization of aminal intermediates in the organocatalytic α-chlorination of aldehydes. These species are stable covalent ternary adducts of the substrate, the catalyst and the chlorinating reagent. NMR-assisted kinetic studies and isotopic labeling experiments with the isolated intermediate did not support its involvement in downstream stereoselective processes as proposed by Blackmond. By tuning the reactivity of the chlorinating reagent, we were able to suppress the accumulation of rate-limiting off-cycle intermediates. As a result, an efficient and highly enantioselective catalytic system with a broad functional group tolerance was developed.

The use of neat BrCl in organic and inorganic chemistry is limited due to its gaseous aggregate state and especially its decomposition into Cl 2 andB r 2 .T he stabilization of BrCl in form of reactive ionic liquidsv ia an ovel in situ synthesis route shifts this equilibrium drastically to the BrCl side, which leads to safer and easier-to-handle interha-logenation reagents. Furthermore, the crystallined erivatives of the hitherto unknown [Cl(BrCl) 2 ] À and [Cl(BrCl) 4 ] À anions were synthesized and characterized by single-crystal X-ray diffraction (XRD), Ramana nd IR spectroscopy,a sw ell as quantum chemical calculations.

A comprehensive analysis of the organocatalytic α‐chlorination of aldehydes with N‐chloroimides and differ‐ ent catalysts is presented. For this reaction, alternate mechanisms were proposed that differ in the role of resting state intermediates and the rationalization of the observed enantioselectivity. This manuscript aims at resolving these funda‐ mental questions on the basis of rigorous structural characterization of intermediates (configuration and conformation), NMR studies, ion mobility‐mass spectrometry, concentration profiles, isotope studies, and DFT calculations. <br>

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A total synthesis of 3-epi-hypatulin B, a highly oxygenated and densely functionalized bicyclic scaffold, is reported. The carbon skeleton was prepared by functionalization of a cyclopentanone core and an intramolecular Mukaiyama aldol reaction. The synthesis features a late-stage photo-oxidation of a methoxyallene intermediate for the installation of an ester functionality. Problems encountered during the batch process were solved by translation of the transformation into a flow protocol. Our synthesis highlights the value of flow chemistry to enable challenging steps in natural product synthesis.