Aromatic bisphosphines

The Wittig-Horner procedure, starting from bisphosphonate or aromatic bisphosphine oxide monomers, allows for AA/BB-coupling of the PO-activated bismethylene monomers, not only with aromatic dialdehydes but also with aromatic diketones to the corresponding PPV derivatives (76), and for the selfcondensation of AB-type aromatic starting compounds containing both alde-hyde/keto and PO-activated methylene functions [101]. 

Second Generation Catalysts Bearing Aromatic Bisphosphines 372... 

Second Generation Catalysts Bearing Aromatic Bisphosphines 9.73.2.1 Animation of aryl halides... 

The first palladium-catalyzed formation of aryl alkyl ethers in an intermolecular fashion occurred between activated aryl halides and alkoxides (Equation (28)), and the first formation of vinyl ethers occurred between activated vinyl halides and tin alkoxides (Equation (29)). Reactions of activated chloro- and bromoarenes with NaO-Z-Bu to form /-butyl aryl ethers occurred in the presence of palladium and DPPF as catalyst,107 while reactions of activated aryl halides with alcohols that could undergo /3-hydrogen elimination occurred in the presence of palladium and BINAP as catalyst.110 Reactions of NaO-/-Bu with unactivated aryl halides gave only modest yields of ether when catalyzed by aromatic bisphosphines.110 Similar chemistry occurred in the presence of nickel catalysts. In fact, nickel catalysts produced higher yields of silyl aryl ethers than palladium catalysts.108 The formation of diaryl ethers from activated aryl halides in the presence of palladium catalysts bearing DPPF or a CF3-subsituted DPPF was also reported 109... 

Four classes of catalysts have been used for the coupling of amines and related nitrogen nucleophiles witii aryl halides. Initially, complexes of the hindered monodentate aromatic tri-ortlio-tolylphosphine catalyzed the reaction of aryl bromides with secondary amines in the presence of an alkoxide or silylamide base. The use of this catalyst for this type of coupling to form C-N bonds was based on an earlier report of the reaction of aryl bromides with tin amides in the presence of a palladium complex of the same ligand as catalyst. - Later, complexes containing aromatic bisphosphines, such as BINAP and dppf, were... 

The nucleophile assisted ring-opening reactions of phosphonate bearing phthahmide 13 has been utihzed in the synthesis of mixed primary phosphine-phosphonate and aromatic amide functionahzed primary bisphosphines as out-hned in Scheme 6 [50],... 

The regioselectivity of hydroesterification of alkyl acrylates or aromatic olefins catalyzed by [PdCl2L2] complexes (L = phosphine ligand) could be largely controlled by variation of the ligands. Triphenylphosphine promotes preferential carboxylation to the branched isomer, whereas with bidentate bisphosphines the linear product is produced overwhelmingly [14]. 

Melhado et al. [100] reported an enantioselective Au(l)-catalyzed Mannich reaction employing spiro bisphosphines ligands (i )-21b, which provides direct access to aliphatic and aromatic a,p-diamino acid derivatives in high diastereo- and enantioselectivities (Scheme 37). 

Aluminium-BINOL-based complexes have also been shown to be highly selective bifunctional asymmetric cyanation catalysts. For example the bisphosphine oxide (6.65) developed by Shibasaki and coworkers catalyses the cyanation of both aromatic and aliphatic aldehydes with ees ranging from 83-98%. ... 

Nickel bisphosphine complexes are used as catalysts in cross-coupfing of aromatic and olefinic halides with Grignard reagents. Kumada and co-workers [69] reported a cross-coupling reaction... 

The copper-catalyzed asymmetric hydrophosphonylation of ketimines has been reported (Scheme 4.120) [198]. Shibasaki used a readily available copper precursor in combination with a resolved bisphosphine to promote the addition reaction. For most of the examples, the authors selected ketimines that incorporated a small alkyl group on one side of the ketamine and an aromatic group on the other side. This substrate design may have contributed to the selectivity of the overall reaction [192,193]. When they moved to substrates that reduced the steric bulk around the ketamine, the selectivity was reduced as well. The reactions occurred at mild conditions (room temperature) with a very low catalyst loading (0.5%). Due to the availability of the precursors, low catalyst loading, high conversions, high selectivity, and mild conditions, this is a very attractive catalyst system for the hydrophosphonylation of ketimines. 

Importantly, asymmetric variants of the foregoing reactions have been developed by using the cationic or neutral rhodium(I)/axially chiral biaryl bisphosphine complexes as catalysts. Although the rhodium-based catalysts are expensive, these are highly stable and can be handled readily using conventional laboratory equipment. Therefore, I believe that rhodium-catalyzed [2 - - 2 - - 2] cycloaddition reactions wiU be employed continuously for the synthesis of complex aromatic compounds. 

Iridium(I) and rhodium(I) catalyst systems make it possible to use commercially available and stable chiral bisphosphine ligands. This feature is favorable for catalyst tuning and facile operation. Further development and application of the atrop-selective aromatization reactions, including [2 - - 2 - - 2]-cycloaddition reactions, are expected in organic synthesis. 

The optimized catalyst 26a showed excellent enantioselectivities and activities in the hydrogenation of a variety of aromatic ketones (Table 5.7). This catalyst was particularly effective for the stericahy hindered substrate. For example, 97% ee of the products have been obtained in the hydrogenation of both 2 -methylacetophenone 23b and 1-acetonaphthone 23n. Complete chirality induction from enantiopure 1,2-diamine to achiral bisphosphine ligand in catalyst 26a was observed in both solid state (see Figure 5.5) and solution. The coordination of C=0 to the cationic... 

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