Stabilization of a Chiral Dirhodium Carbene by Encapsulation and a Discussion of the Stereochemical Implications |
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Authors: | Dr Christophe Werlé Dr Richard Goddard Petra Philipps Dr Christophe Farès Prof Alois Fürstner |
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Institution: | Max-Planck-Institut für Kohlenforschung, Mülheim/Ruhr, Germany |
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Abstract: | For the first time, the stereochemical course of an asymmetric cyclopropanation can be discussed on the basis of experimental structural information on a pertinent chiral dirhodium carbene intermediate. Key to success was the formation of racemic single crystals of a heterochiral Rh2{(S*)‐PTTL}4{=C(Ar)COOMe}]Rh2{(R*)‐PTTL}4] (Ar=MeOC6H4; PTTL=N‐phthaloyl‐tert‐leucinate) capsule, which has been characterized by X‐ray diffraction. NMR spectroscopic data confirm that the obtained structural portrait is also relevant in solution and provide additional information about the dynamics of this species. The chiral binding pocket is primarily defined by the conformational preferences of the N‐phthaloyl‐protected amino acid ligands and reinforced by a network of weak interligand interactions that get stronger when chlorinated phthalimide residues are used. |
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Keywords: | asymmetric synthesis carbenes cyclopropanes reactive intermediates rhodium |
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