Phosphoramidite ligands hydrovinylation

Scheme 9.4 chiral phosphoramidite ligands used in hydrovinylation of styrenes. 

In addition to the extensive studies of hydrovinylations using styrene substrates, 1,3-dienes are also an especially useful substrate class. With phosphoramidite ligands, enantioselective diene hydrovinylation with ethylene provides a practical solution to the difficulties associated with the installation of exocyclic side chain stereochemistry, as the representative procedure below illustrates. ... 

Scheme 5.2 Hydrovinylation of vinylarenes with an in situ generated nickel catalyst from a phosphoramidite ligand derived from Feringa s ligand.

Scheme 5.12 Hydrovinylations of steroid 1,3-dienes with in situ generated nickel catalysts from phosphoramidite ligands.

At present, phosphoramidites represent the most promising ligand class for the hydrovinylation reaction, both for the excellent activities and enanioselectivities. The synthetic potential embraces not only styrene and styrene derivatives but also norbornene [54] and 1,3-dienes [55]. 

In 2009, P-chiral phosphorus triamide ligands were applied in Ni-catalyzed asymmetric hydrovinylation of styrene with promising results, good yields (77%), and good enantioselectivity (up to 63% ee). Recently, phosphoramidite and P-stereogenic phosphorodiamidite ligands L17 and L18 derived from (Sj-2-phenylamino-2 -hydroxy-l,l -binaphthyl (7y-Ph-NOBIN) and bis(l-phenyl-ethyl)amine were synthesized and applied in asymmetric hydrovinylation of styrene, leading to almost perfect selectivity and enantioselectivity (up to 91% ee) (Scheme 9.5). ... 

Scheme 9.5 NOBIN-based phosphoramidite and phosphorodiamidite ligands used in asymmetric Ni-catalyzed hydrovinylation.

Recently, RajanBabu and co-workers successfully realized the enantioselective syntheses of biologically relevant molecules such as pseudopterosin G-J (Scheme 9.10) and indole alkaloids cis-trikentrin A and B (Scheme 9.11) by using Ni-catalyzed asymmetric hydrovinylation reaction as the key step. The utilization of binaphthol phosphoramidite (S,l a) L15 as the chiral ligand, in combination with NaBARF as the halide abstractor, was critical to achieve high regio- and enantioselectivity under very mild reaction conditions. ... 

In 2005, the Zhou group applied the biindane-derived ehiral spiro phosphoramidite and phosphite ligands in the Pd-catalyzed asymmetric hydrovinylation of styrene. However, only moderate yield and enantiose-lectivity could be obtained. Recently, Muller and co-workers synthesized Cj-symmetric tris-binaphthyl monophosphite ligand L29, and used it in the Pd-catalyzed asymmetric hydrovinylation reaction. The hydrovinylation product of styrene could be obtained in 70% conversion and 92% ee (Scheme 9.12). ... 

In 2007, Leitner et al. reported the synthesis of novel monodentate Quina-phos phosphoramidites bearing different substituents in the 2-position of the 1,2-dihydroquinoline backbone. These ligands were further investigated in the enantioselective nickel-catalysed hydrovinylation of styrene in the presence of NaBArF. Among them, Cl-Quinaphos phosphoramidite bearing an n-butyl substituent in the 2-position of the 1,2-dihydroquinoline backbone, was demonstrated as optimal, providing the corresponding 3-phenylbut-l-ene in enantioselectivity of 91% ee and almost quantitative yield, as shown in Scheme 5.4. 

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