Absolute Asymmetric Synthesis of a Tetrahedral Silver Complex

Abstract

Even though the isolation of tetrahedral stereoisomers usually presents a synthetic challenge, a highly enantioenriched tetrahedral silver complex could be easily accessed by either crystallization or Viedma ripening. The overall preparation may be regarded as an example of absolute asymmetric synthesis. Experimental results indicate that both crystallization and Viedma ripening follow a similar cluster-controlled mechanism.

Spontaneous Deracemizations

“…Ethylenediammonium sulfate was the first compound other than NaClO 3 and NaBrO 3 for which the phenomenon was detected. , To the best of our knowledge, all commercial achiral organic compounds forming racemic conglomerates tested under Viedma grinding conditions have led to deracemization and no negative results have been reported. Viedma deracemization has also been reported to occur in the case of tetrahedral and octahedral chiral transition metals , and also in the self-assembly of supramolecular structures formed by achiral coordination ligands and metal cations Reports expanding the method to chiral compounds crystallizing as racemic conglomerates by the coupling with a deracemization of the chiral compounds in solution (Figure ).…”

Absolute Autocatalytic Amplification under Heterogenous Phase Conditions Involving Subsequent Hydride Transfer and a Hemiacetal Intermediate

“…The decisive stage showing spontaneous molecular symmetry breaking (SMSB) is the formation of the racemic conglomerate from the racemic mixture of enantiomers. [5] Enantioenrichment is also possible by selective crystallization or sublimation. [6] To date, the Soai reaction offers the only example of an absolute asymmetric catalytic reaction in absence of chiral polarization in the alkylation of pyrimidinyl aldehyde 1 into alkanol 2.…”

Deracemisations under kinetic and thermodynamic control

“…This secondary nucleation process was beautifully illustrated by McBride using video recordings. 27 Since Havinga's first observations, spontaneous deracemisation of conglomerate forming compounds has been discovered for several compounds comprising asymmetric centra [28][29][30] but also for atropisomers, 21,31 metal complexes, 32,33 helical coordination polymers, 34 and even helical oligomers. 35 Deracemisations often proceeded faster and more reliably when stirring was conducted during the crystallisation process.…”

“…Viedma ripening is not limited to compounds with a racemisable sp 3 stereocenter: metal-based complexes that racemise spontaneously in solution were readily deracemised in abrasive grinding conditions as well. 33,61 Finally, the groups of Vlieg and Kellogg showed that precursors to important pharmaceuticals such as naproxen, 62 clopidogrel, 63 and prasugrel 64 can be readily deracemised using the Viedma ripening process highlighting the industrial relevance of attrition-enhanced deracemisations (Fig. 6).…”