QUINAP-type ligands

In a new departure in the quest for QUINAP-type ligands with an electron-deficient phosphorus atom, a novel QUINAP-derived triarylphosphite ligand 73 (Figure 10) was developed by Brown 10 years after the parent ligand 60 was first reported.100... 

Ligand 73 was prepared directly from a single enantiomer of the corresponding naphthol of QUINAP 60, an early intermediate in the original synthesis, and both enantiomers of BINOL. Application in hydroboration found that, in practice, only one of the cationic rhodium complexes of the diastereomeric pair proved effective, (aA, A)-73. While (aA, A)-73 gave 68% ee for the hydroboration of styrene (70% yield), the diastereomer (aA, R)-73 afforded the product alcohol after oxidation with an attenuated 2% ee (55% yield) and the same trend was apparent in the hydroboration of electron-poor vinylarenes. Indeed, even with (aA, A)-73, the asymmetries induced were very modest (31-51% ee). The hydroboration pre-catalyst was examined in the presence of catecholborane 1 at low temperatures and binuclear reactive intermediates were identified. However, when similar experiments were conducted with QUINAP 60, no intermediates of the same structural type were found.100... 

The author expected that a reaction with a chiral ligand which coordinates to a copper atom could produce optically active 2-(aminomethyl)indoles. Knochel recently developed a novel asymmetric synthesis of chiral propargylamines with excellent ee values through a copper-catalyzed asymmetric Mannich-type reaction of alkynes with an aldehyde and a secondary amine using QUINAP as a chiral ligand (up to 98% ee) [1-3]. Carreira reported the similar synthesis of propargylic amine in up to 99% ee with PINAP [4, 5]. The author initially examined the... 

Other systems different from oxazolidinones have been successfully applied as ligand of Cu(I) salts for this transformation. The use of QUINAP (L in Scheme 11.15), combined with CuBr gave excellent results in the total synthesis of (S)-(-l-)-coniine, a highly toxic alkaloid inducing curare-type paralysis, in 45% overall yield and 90%... 

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