We thank the Deutsche Forschungsgemeinschaft (DFG) for their financial support (EXC81, SFB623). We also acknowledge Stephen Hashmi (Heidelberg University) for fruitful discussions. Volker Huch is gratefully acknowledged for X-ray crystallography. Michael Schwering and Dominik Brox have continuously supported the project with their expertise in microscopy.Supporting information for this article, including details of reagents used, instruments, and analytical data, including spectroscopic characterization, is available on the WWW under http://dx.

Stereolabile interconverting catalysts open up the possibility of directing enantioselectivity in asymmetric synthesis by formation of diastereomeric complexes with chiral auxiliaries and deracemization. However, the stoichiometrically used auxilliaries can significantly limit the potential applications of such systems. We synthesized a new BIPHEPO tropos ligand containing achiral selectands in the backbone, which forms transient diastereomeric associates with amylose-tris-3,5-dimethylphenyl carbamate as a selector and thus deracemizes. The enantiomerically enriched BIPHEPO obtained was successfully used in the organocatalytic asymmetric double aldol addition of substituted methyl ketones to form benzaldehyde. This strategy combines an on-column deracemization with the high stereoinduction of chiral biarylphosphineoxides and opens up new possibilities in the field of self-amplified asymmetric syntheses.

Chemical reactions that lead to as pontaneous symmetry breaking or amplification of the enantiomeric excess are of fundamental interesti ne xplaining the formation of ah omochiral world.Ano utstanding example is Soai's asymmetric autocatalysis, in which small enantiomerice xcesses of the added product alcohol are amplified in the reaction of diisopropylzinc and pyrimidine-5-carbaldehydes. The exact mechanism is still in dispute due to complex reaction equilibria and elusive intermediates. In situ high-resolution mass spectrometric measurements, detailed kinetic analyses and doping with in situ reacting reaction mixtures show the transient formationo fh emiacetal complexes, whichc an establish an autocatalytic cycle.W ep ropose a mechanism that explainst he autocatalytic amplification involving these hemiacetal complexes.C omprehensivek inetic experiments and modelling of the hemiacetal formation and the Soai reactiona llow the precise predictiono ft he reaction progress, the enantiomeric excessa sw ell as the enantiomeric excess dependentt ime shift in the induction period. Experimental structurald ata give insights into the privileged properties of the pyrimidyl units and the formationof diastereomeric structures leading to an efficient amplification of even minimalenantiomeric excesses, respectively.

Dynamics and kinetics in a single stroke: The stereodynamics of the tropos‐chiral diphosphine biphep and its 3,3′‐dialkoxy analogues were investigated by enantioselective dynamic HPLC (DHPLC) and a novel three‐column approach, in with the dynamics and kinetics of the interconversion were examined in a single experimental setup (see scheme).

We investigated the stereodynamics of 5,5'-substituted tropos BIPHEP ligands (2,2'-bis(diphenylphosphino)-biphenyls) by enantioselective dynamic high-performance liquid chromatography (DHPLC) to elucidate the influence of the substitution pattern and electronics of the substituents (methyl, methoxy, and hydroxyl groups). By temperature-dependent dynamic HPLC measurements the activation parameters ΔG(╪), ΔH(╪), and ΔS(╪) could be determined with high precision, revealing that the activation barrier of these 5,5'-substituted BIPHEP ligands ranges in a narrow band between 87.8 and 93.0 kJ mol(-1), making them highly attractive as deracemizable dynamic chiral ligands in asymmetric catalysis. Interestingly, the activation parameters are highly influenced by a hydroxyl or methoxy group in the 5,5'-position of the BIPHEP ligands.