Asymmetric Hydrocyanation of Olefins

Two Pd(0)-DIOP complexes (Scheme 2), Pd(diop)2 (1)PLW] and Pd(i7 -CH2=CH2) (diop) (2),t which were catalysts of asymmetric hydrocyanation of olefins, were reported... 

Examples include acetal hydrolysis, base-catalyzed aldol condensation, olefin hydroformylation catalyzed by phosphine-substituted cobalt hydrocarbonyls, phosphate transfer in biological systems, enzymatic transamination, adiponitrile synthesis via hydrocyanation, olefin hydrogenation with Wilkinson s catalyst, and osmium tetroxide-catalyzed asymmetric dihydroxylation of olefins. 

In the metal catalyzed hydrocyanation area, the stage is set for major improvements in enantioselectivity for simple styrene derivatives. Asymmetric hydrocyanation of dienes and functionaUzed olefins is another exciting area ripe for further explorations. 

Asymmetric catalyzed hydrocyanation of prochiral olefins usually gives disappointing selectivities. However, RajanBabu and Casalnuovo [1344] have recently performed asymmetric hydrocyanation of 2-vinylnaphthalenes under Ni(cod)2 catalysis in the presence of phosphinite 3.33 (Ar = 3,5-(CF3>2C6H3). These hydrocyanations occur with a high regio- and enantioselectivity (Figure 7.21), and the major product is obtained in enantiopure form by fractional ciystalli-zation. 

Chiral Catalysts Containing Group 10 Metals (Ni, Pd, and Pt). The catalyst formed in situ from Ni(acac)2 and bomane aminoalcohols (DAB or DAIB) catalyze the enantioselective addition of diethylzinc to chalcones (254) (Fig. 21). Nickel(II)-chiral Schiff-base (the ligand derived from 1,2-diaminocyclohexane or 1,2-diaminopropane with pyrone derivative) complexes were efficient in epoxida-tion of nonfunctionalized olefins (255). Bis-ferrocenyl-triphosphane (PIGIPHOS) formed catalytically active complex with Ni(II) (256). Nickel-catalyzed asymmetric hydrocyanation of vinylarenes using glucose-derived phosphinite ligands was observed (257). 

The asymmetric reactions discussed in this chapter may be divided into three different types of reaction, as (1) hydrometallation of olefins followed by the C—C bond formation, (2) two C C bond formations on a formally divalent carbon atom, and (3) nucleophilic addition of cyanide or isocyanide anion to a carbonyl or its analogs (Scheme 4.1). For reaction type 1, here described are hydrocarbonyla-tion represented by hydroformylation and hydrocyanation. As for type 2, Pauson-Khand reaction and olefin/CO copolymerization are mentioned. Several nucleophilic additions to aldehydes and imines (or iminiums) are described as type 3. 

The potential naproxen precursor 23 is accessible in 96 % yield and in 85 % ee by asymmetric hydrocyanation (cf. Section 2.5) of the aromatic olefin 22 catalyzed by a Ni° complex with a glucose-derived phosphinite ligand (Scheme 6) [27]. 

Olefin hydrocyanation using palladium catalysts has been less well studied than with nickel. Nevertheless, zerovalent complexes of palladium, particulrly triarylphosphite complexes, hydrocyanate a wide range of olefins in useful yields (see Table 1). Early work reported the merit of excess phosphorus ligand to promote the reaction, and further paralleling the observations with nickel, Lewis acids have been used to improve catalytic activity. However, addition of ZnClj fails to improve nitrile product yield . Asymmetric induction in hydrocyanation results in optical yields of 30% in the synthesis of exo-2-cyanonorbomane using the chiral ligand DIOP, and studies on the stereochemistry of HCN and DCN addition to terminal alkenes and a substituted cyclohexene with the same catalyst have been reported. ... 

The enantioselective hydrocyanation of alkenes has the potential to serve as an efficient method to generate optically active nitriles, as well as amides, esters, and amines after functional group interconversions of the nitrile group. As in asymmetric hydroformylation, asymmetric hydrocyanation requires control of both regiochemistry and stereochemistry because simple olefins tend to generate achiral terminal nitrile products. The hydrocyanation of norbomene will give a single constitutional isomer and was studied initially. However, modest enantioselectivities were obtained, and the synthetic value is limited. ... 

Profenes or aryl-2-propionic acids are a family of antiinflammatory agents representing an enormous market in pharmacy. Several approaches of syntheses of these compounds using asymmetric catalysis have been used with success. For example, asymmetric hydrocyanation (see Chap. 14) of an olefin by nickel(O) to which a phosphinite ligand derived from glucose is coordinated leads to a nitrile precursor of naproxene with a 96% yield and 85% e.e. ... 

Isomerization via homogeneous catalysts occurs, for instance, as 2ui intermediate step in catalytic processes. Thus in Shell s hydroformylation route, which converts internal olefins to primary alcohols, isomerization takes place prior to CO-insertion. Homogeneous isomerization of 2-me-thyl-3-butenenitrile to the linear nitrile is an essential step in du Font s hydrocyanation. Noteworthy is the recent commercial asymmetric isomerization of neryl and geranyl amines [3]. 

Naproxen. In addition, the use of chiral bisphosphites in asymmetric olefin hy-drocyanation is described. Details of the structural features responsible for hi b/1 and %ee in asymmetric hydroformylation and hydrocyanation are presented. 

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