Ligands synthesis phosphine-acetals

Figure 5.12 Synthesis of immobilized dinuclear rhodium(ll) complexes bearing ortho-metallated phosphine ligands (axial acetic acid ligands omitted for clarity). (Redrawn from Nowotny et al. [64].)...

From a practical standpoint, it is of interest to devise a one-step synthesis of the catalyst. Since both reactions 2 and 3 are ligand substitution reactions, it is quite conceivable that both steps can be carried out at the same time. When we reacted [Ru(COD)Cl2]n with BINAP and sodium acetate in acetic acid, we indeed obtained Ru(BINAP)(OAc)2 in good yields (70-80%). Interestingly, when the reaction was carried out in the absence of sodium acetate, no Ru(BINAP)(OAe)2 was obtained. The product was a mixture of chloro-ruthenium-BINAP complexes. A 3ip NMR study revealed that the mixture contained a major species (3) (31P [ H] (CDCI3) Pi=70.9 ppm P2=58.3 ppm J = 52.5 Hz) which accounted for more than 50% of the ruthenium-phosphine complexes (Figure 2). These complexes appeared to be different from previously characterized and published Ru(BINAP) species (12,13). More interestingly, these mixed complexes were found to catalyze the asymmetric hydrogenation of 2-(6 -methoxy-2 -naphthyl)acrylic acid with excellent rates and enantioselectivities. 

The palladium-catalyzed coupling of silyl ketene acetals with aryl bromides in the presence of TlOAc has been applied to the asymmetric synthesis of 2-aryl-propionic acids (40—50% ee) by the use of BPPFA and several other chiral phosphine ligands (Scheme 2-16) [35]. 

Miscellaneous Methods of Preparing Phosphines. - The synthesis and properties of phosphorus-containing cryptand ligands has been reviewed. The basic principles for the synthesis of functionalised phosphorus-containing heterocyclic systems have been summarised, relating to the chemistry of phosphabicyclohexanes, dihydrophosphinines, phosphabicyclooctadienes, and phosphabicyclooctenes °. Ethylene acetals (108) of the 9-oxa-2-phosphabicyclo[4.4.0]-5-one system have been prepared. Methods for the... 

Activated methylene compounds such as dimethyl malonate have found substantial utility in palladium catalyzed allylic substitution reactions. Accordingly, the Krapcho decarboxylation is often used in conjunction with these reactions. As an example, the first total synthesis of enantiomerically pure (-)-wine lactone has utilized the sequence of reactions.27 First, the allylic substitution reaction of 2-cyclohexen-l-yl acetate (49) with alkali sodium dimethylmalonate yielded 51 with high enantioselectivity, as a result of the use of chiral phosphine ligand 50. The malonate was then subjected to Krapcho decarbomethoxylation using NaCl, H2O, and DMSO at 160 °C to yield 52. This reaction has been used similarly following the allylic substitution reaction with other malonate derivatives.28-30... 

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