The First Spiro Isoxazoline Ligands

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We had great interest in the chelating ability of isoxazolines on the basis of ab initio calculations. In this project, we have designed, and synthesized the first chiral bis(isoxazoline) ligands (SPRIXs) containing rigid spiro skeleton. The ligands showed great affinity towards Pd(II) salts and the resulting chiral Pd(II)-spiro bis(isoxazoline) catalysts promoted the catalytic asymmetric Wacker-type cyclization of alkenyl alcohols. Furthermore, a new catalytic asymmetric tandem cyclization of dialkenylalcohol took place, affording a unique bicyclic ether in one step with up to 95% ee. New type of bis(isoxazoline) ligands, 2,2'-bis(isoxazolinyl)propane and (R)-2,2'-bis(isoxazolinyl)-1,1'-binaphthyl have been prepared and strong ligand-acceleration effects were demonstrated in Pd(II)-catalyzed Wacker-type cyclization of alkenyl alcohol. The lack of acceleration effects with oxazoline ligands clearly shows the crucial role of isoxazoline moiety on the Wacker-type cyclization of alkenyl alcohols. In the presence of carbon monoxide the Pd(II)-spiro bis(isoxazoline) catalyst also promoted the asymmetric carbonylation of alkenyl amines or alcohols to give pyrrolidines or lactones with moderate enantioselectivities.