Complexes phosphoramidite-rhodium

The 4-I-2-cycloaddition of trimethylsilyl (TMS)-substituted cyclopentadiene with phosphorylated nitroso alkenes formed bicyclo 1,2-oxazines. However, as dienophiles, phosphorylated nitroso alkenes also react with cyclopentadiene and cyclohexadiene. The phosphoramidite-rhodium complex (84)-catalysed 4- -2-cycloaddition of a,fi-unsaturated imines with isocyanates produced pyrimidinones in good yields and with high enantioselectivities. ... 

In contrast, iridium complexes of phosphoramidite ligands catalyze the enantiose-lective formation of the branched allyUc substitution products with high enantiomeric excess. Takeuchi and Helmchen " - - - reported that iridium complexes, hke rhodium complexes, generate the chiral, branched product from reactions of mono-substituted aUylic acetates and carbonates with carbon and nitrogen nucleophiles (Equations 20.45-20.47). 

Phosphoramidites, a ligand class that has only recently been introduced into asymmetric hydrogenation, in the form of hybrid chelate ligands [29], induce excellent enantioselectivity as monodentate ligands. Thus de Vries, Feringa, and co-workers could reduce standard substrates in >96% ee with a rhodium complex based upon the binaphtholphosphoramidite 3d, once the solvent and reaction temperature had been optimized [30],... 

Reek et al.73 developed a new bicarbazolediol-74 (BICOL)-based, chiral monodentate phosphoramidite ligand, in which the Ai-sites in the bicarbazole skeleton permitted the easy introduction of metal centers. As a model reaction, the Rh-catalyzed asymmetric hydrogenation of methyl 2-acetamidocinnamate was evaluated. Using a ligand to rhodium ratio of 2.2, the enantioselectivity induced by the rhodium complex (Figure 10.7) was 93% at full conversion,... 

In terms of the analysis of phosphoramidates, an electrospray mass spectrometric method for accurate mass determination of highly acid-sensitive phosphoramidates has also been developed a through-space F-Sip spin-spin coupling NMR investigation has been conducted for BINOL-3,3,triflone A, A -dimethylphosphoramidites and NMR spectroscopy, X-ray dilfraction and DFT calculations have all been used to probe the bonding interactions in palladium, platinum and rhodium phosphoramidite complexes. 

Scheme 3.80 Catalytic asymmetric intramolecular hydroacylation with rhodium/phosphoramidite-alkene ligand complexes.

A neutral rhodium(I)/phosphoramidite (9) complex was found to be a highly effective catalyst for the highly regioselective intermolecular [2 + 2 + 2] cycloaddition of terminal alkynes with isocyanates (Scheme 4.72) [61],... 

In 2006, EUman, Bergmann, and coworkers reported the synthesis of a PKC inhibitor by using a rhodium-catalyzed intramolecular C-H alkenylation at the C2 position of the indole moiety (Scheme 16.4) [13]. Imine 19, which was prepared from the corresponding aldehyde and a benzylamine, was treated with a rhodium complex and phosphoramidite ligand 20 in toluene, followed by hydrolysis of the imine group under acidic conditions to afford 22 in 61% yield with 90% ee (over two steps). Mechanistically, imine 19 directed the rhodium-catalyzed C-H activation via intermediate 21, with subsequent intramolecular alkylation to give the desired product 22. Thereafter, the synthesis of the target PKC inhibitor from 22 over several steps has been accomplished. 

The active catalyst is presumably a cationic complex with a 1 1 phosphine/ rhodium ratio. The phenyl substituent of the chiral phosphoramidite ligand Lll seems to play an important role for stereocontrol. Therefore, it has been postulated that t[ -coordination of the phenyl group takes place during the catalytic cycle and helps to create a well defined chiral environment (Fig. 10.40). 

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