Journal
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY
Volume 2010, Issue 31, Pages 5996-6004Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/ejoc.201000794
Keywords
Ligand design; Chiral resolution; Chirality; Atropisomerism; Asymmetric synthesis; Palladium; Hydroboration
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The synthesis of four new members of the Quinazolinap series of ligands is described. Three of these ligands were prepared by post-resolution modification of the known ligand (R) -7-chloro-2-isopropyl-Quinazolinap, a new approach which offers an expedient route to a range of enantiopure ligands as it precludes the need for resolution of each ligand prepared. The remaining ligand, 7-chloro-2-methyl-Quinazolinap, was prepared in a seven-step synthetic sequence incorporating palladium- and nickel-catalyzed transformations as the key steps. A diastereomerically pure palladacycle of this ligand was characterised by X-ray crystallography. (R)-7-Chloro-2-isopropyl-Quinazolinap was applied to the rhodium-catalyzed hydroboration of vinylarenes with regioselectivities of up to > 99:1 and ee values of up to 68 %. Each of the Quinazolinap ligands prepared were applied to the palladium-catalyzed allylic alkylation of 1,3-diphenylprop-2-enyl acetate resulting in conversions of up to 100% and ee values of up to 85%. Solution-phase NMR studies on a palladium complex of one of the ligands provided a rationale for the sense of asymmetric induction.
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