Cross coupling reactions enantioselective

Negishi E, Tan Z (2005) Diastereoselective, Enantioselective, and Regioselective Carbo-alumination Reactions Catalyzed by Zirconocene Derivatives. 8 139-176 Netherton M, Fu GC (2005)Pa]ladium-catalyzed Cross-Coupling Reactions of Unactivated Alkyl Electrophiles with Organometallic Compounds. 14 85-108 Nicolaou KC, King NP, He Y (1998) Ring-Closing Metathesis in the Synthesis of EpothUones and Polyether Natmal Products. 1 73-104 Nishiyama H (2004) Cyclopropanation with Ruthenium Catalysts. 11 81-92 Noels A, Demonceau A, Delaude L (2004) Ruthenium Promoted Catalysed Radical Processes toward Fine Chemistry. 11 155-171... 

Phosphine ligands based on the ferrocene backbone are very efficient in many palladium-catalyzed reactions, e.g., cross-coupling reactions,248 Heck reaction,249 amination reaction,250 and enantioselective synthesis.251 A particularly interesting example of an unusual coordination mode of the l,l -bis(diphenylphosphino)ferrocene (dppf) ligand has been reported. Dicationic palladium(II) complexes, such as [(dppf)Pd(PPh3)]2+[BF4 ]2, were shown to contain a palladium-iron bond.252,253 Palladium-iron bonds occur also in monocationic methyl and acylpalladium(II) complexes.254 A palladium-iron interaction is favored by bulky alkyl substituents on phosphorus and a lower electron density at palladium. 

Aromatic and vinylic sulfides take part in cross-coupling reactions with Grignard reagents in the presence of Ni catalysts.336,337 This reaction has been applied to the enantioselective synthesis of binaphthyls using a standard chiral oxazoline ligand (Equation (25)) 338... 

The use of chiral bidentate phosphines (such as BINAP) in enantioselective cross-coupling reactions has been described, though only modest stereoselectivity has been achieved.431... 

Carbon-carbon bond-forming reactions are one of the most basic, but important, transformations in organic chemistry. In addition to conventional organic reactions, the use of transition metal-catalyzed reactions to construct new carbon-carbon bonds has also been a topic of great interest. Such transformations to create chiral molecules enantioselectively is therefore very valuable. While various carbon-carbon bond-forming asymmetric catalyses have been described in the literature, this chapter focuses mainly on the asymmetric 1,4-addition reactions under copper or rhodium catalysis and on the asymmetric cross-coupling reactions catalyzed by nickel or palladium complexes. 

Figure 3.49. Chiral ligands that exhibit high enantioselectivity in the nickel-catalyzed Grignard cross-coupling reaction of vinyl bromide (or chloride) with 1-phenylethylmagne-sium chloride.

The enantioselective desymmetrization strategy can also be used for the palladium-catalyzed cross-coupling reactions with Grignard reagents. Thus, in the... 

The sequential approach is also common in proposals written by synthetic chemists (a multistep synthesis is inherently step by step). Vyvyan (excerpt 13N), for example, proposes a strategy to synthesize a select group of heliannuols (alleo-pathic natural products isolated from the sunflower) in an optically pure form. One approach that he will explore involves enantioselective cross-coupling reactions between an alkyl zinc reagent and an aryl bromide. He begins with experiments that will utilize recently developed catalysts and produce products with known optical rotation data. Subsequent reactions are described that will lead potentially to the desired stereospecific heliannuols A and D. 

Comins and Green have recently developed a new method for the enantioselective synthesis of 4-substituted phenylalanines based on Pd-catalyzed cross-coupling reactions of a protected boronophenyl alanine with aromatic halides. These reactions proceed with good to excellent yields, and furnish the desired products with high enantiomeric purities [25]. 

Cross-Coupling of Halides. 4,4-Dimethyl-1-phenylpenta-1,2-diene has been prepared using a ((-)-(2f ,3f )-DIOP)PdCl2-catalyzed cross-coupling reaction, although low enantioselectivity was observed (eq 5). ... 

Ferrocenyl-based ligands comprise a versatile class of auxiliaries because they can be easily modified at the benzylic position with retention of configuration and can incorporate both central and planar chiralities. The appropriate balance of steric and electronic factors has provided ferrocenyl derivatives featuring chelating P,N properties that proved beneficial in numerous enantioselective transformations [50]. Among more recent applications, they could be utilized very efficiently in Pd-catalyzed hydrosilylation (14 >99% ee) [51] and hydroboration (>94% ee) [52] of olefins, allylic amination (99 % ee) [53], Suzuki cross coupling reactions (Section 2.11) [54], and enamide hydrogenation (>99% ee) [55]. 

The thiazolium-catalyzed addition of an aldehyde-derived acyl anion with a Michael acceptor (Stetter reaction) is a well-known synthetic tool leading to the synthesis of highly funtionalized products. Recent developments in this area include the thiazolylalanine-derived catalyst 191 for asymmetric intramolecular Stetter reaction of a,P-unsaturated esters <05CC195>. However, these cyclizations proceed only in moderate enantioselectivities and yields even under optimized conditions. Thiazolium salt 191 has been used successfully for enantioselective intermolecular aldehyde-imine cross coupling reactions <05JA1654>. Treatment of tosylamides 194 with aryl aldehydes in the presence of 15 mol% of 191 and 2... 

A single attempt has been made to induce asymmetry in the intermolecular cross coupling reaction by employing a chiral ligand for the samarium ketyl [56]. Utilizing 2,2 -bis(diphenylphosphinyl)-l,l -binaphthyl (BINAPO) as a chiral ligand, a modest start has been made to develop an enantioselective process. However, in the examples reported to date the method is plagued by low yields and/or moderate stereoselectivities. 

The compound 12 is an extremely useful ligand for nickel-catalyzed Grignard cross-coupling reactions and allows the enantioselective synthesis of biaryls in over 90%ee36,37 (Sections D. 1.1.3. and B.2.). 

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