A strategy for the stereoselective preparation of enantiomerically enriched cis-2,6-disubstituted piperazines from amino acid precursors is described. The target compounds are generated in 95-99% ee with good to excellent levels of diastereoselectivity (usually 14:1 to >20:1) using Pd-catalyzed carboamination reactions between aryl or alkenyl halides and substituted ethylenediamine derivatives to form the heterocyclic rings. The synthesis requires only 4-5 steps from commercially available amino acids, and allows for the modular construction of piperazines bearing different substituents at N(1), N(4), C(2), and C(6). The use of this strategy for the construction of 2,3-disubstituted piperazines, fused bicyclic piperazines, and tetrahydroquinoxalines is also reported. In addition, the mechanism of the key carboamination reactions are discussed, and new models that predict and explain the stereochemical outcome of these transformations are presented.
A strategy for the stereoselective preparation of enantiomerically enriched cis-pan class="Chemical">2,6-disubstituted piperazines from amino acid prepan class="Chemical">cursors is described. The target compounds are generated in 95-99% ee with good to excellent levels of diastereoselectivity (usually 14:1 to >20:1) using Pd-catalyzed carboamination reactions between aryl or alkenyl halides and substitutedethylenediamine derivatives to form the heterocyclic rings. The synthesis requires only 4-5 steps from commercially available amino acids, and allows for the modular construction of piperazines bearing different substituents at N(1), N(4), C(2), and C(6). The use of this strategy for the construction of 2,3-disubstituted piperazines, fused bicyclic piperazines, and tetrahydroquinoxalines is also reported. In addition, the mechanism of the key carboamination reactions are discussed, and new models that predict and explain the stereochemical outcome of these transformations are presented.
Authors: Alma Viso; Roberto Fernández de la Pradilla; Aida Flores; Ana García; Mariola Tortosa; María L López-Rodríguez Journal: J Org Chem Date: 2006-02-17 Impact factor: 4.354