13685-97-7Relevant academic research and scientific papers
Chiral diphosphorus compounds and their transition metal complexes
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Page/Page column 14, (2010/02/11)
The present invention relates to chiral diphosphorus compounds and their transition metal complexes, to a process for preparing chiral diphosphorus compounds and their transition metal complexes and also to their use in asymmetric syntheses.
Chiral diphosphorus compounds and transition metal complexes thereof
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Page 24, (2010/02/05)
Tetrahydrofuran bisphosphines of formula (I), are new. Tetrahydrofuran bisphosphines of formula (I): X1, X2 = bonds or O; R1, R2 = H, 1-20C alkyl, 1-20C fluoroalkyl, 2-20C alkenyl, 4-24C aryl, 5-25C aralkyl, 6-26C aralkenyl, NR7R8, OR8, AOR8, ANR7R8 or OC
Carbohydrate Phosphinites as Practical Ligands in Asymmetric Catalysis: Electronic Effects and Dependence of Backbone Chirality in Rh-Catalyzed Asymmetric Hydrogenations. Synthesis of R- or S-Amino Acids Using Natural Sugars as Ligand Precursors
RajanBabu,Ayers, Timothy A.,Halliday, Gary A.,You, Kimberly K.,Calabrese, Joseph C.
, p. 6012 - 6025 (2007/10/03)
Vicinal diarylphosphinites derived from carbohydrates are excellent ligands for the Rh(I)-catalyzed enantioselective asymmetric hydrogenation of dehydroamino acid derivatives, producing the highest enantioselectivity of any ligands directly prepared from natural products. The enantioselectivity can be enhanced by the appropriate choice of substituents on the aromatic rings of the phosphinites. For example, the use of phosphinites with electron-donating bis(3,5-dimethylphenyl) groups on phosphorus provides ee's up to 99% for a wide range of amino acids including some with easily removable N-protecting groups. Electron-withdrawing aryl substituents, on the other hand, decrease the enantioselectivity. Sense of chiral induction in the amino acid product depends on the relative juxtaposition of the vicinal diphosphinites on a given sugar backbone. When readily available D-glucopyranosides are used as the starting sugars, 2,3-phosphinites give the S-amino acids and 3,4-phosphinites give the R-amino acids. In the case of aromatic and heteroaromatic amino acids, enantioselectivities > 95% are consistently obtained. Practical considerations such as the ease of ligand synthesis, rates of reactions, catalyst turnover, and scope and limitations in terms of substrates are discussed. A possible explanation for the enhancement of enantioselectivity by electron-rich phosphinites is offered.
Ligand Electronic Effects in Asymmetric Catalysis: Enhanced Enantioselectivity in the Asymmetric Hydrocyanation of Vinylarenes
Casalnuovo, Albert L.,RajanBabu, T. V.,Ayers, Timothy A.,Warren, Timothy H.
, p. 9869 - 9882 (2007/10/02)
The enantioselectivity of the nickel-catalyzed, asymmetric hydrocyanation of vinylarenes using glucosederived, chiral phosphinite ligands, L, increases dramatically when the ligands contain electron-withdrawing P-aryl substituents.The substrate and solvent also strongly influence the enantioselectivity, with the highest ee's (85-91percent for 6-methoxy-2-vinylnaphthalene (MVN)) obtained for the hydrocyanation of electron-rich vinylarenes in a nonpolar solvent such as hexane.Mechanistic studies suggest the catalytic cycle consists of an initial HCN oxidative addition or vinylarene coordination to "NiL", followed by insertion to form an (η3-benzyl)nickel cyanide complex, and irreversible reductive elimination of the nitrile.A kinetic analysis of the NiLa(COD) (La, P-aryl=3,5-(CF3)2C6H3) catalyzed hydrocyanation of MVN indicates that as the HCN concentration is increased the catalyst resting state shifts from NiLa(COD) to a complex containing both MVN and HCN, presumably the (η3-benzyl)nickel cyanide intermediate NiLa(η3-CH3CHC10H6OCH3)CN.A 31P NMR analysis of the intermediate NiLa(MVN) shows little ground state differentiation of the MVN enantiofaces and suggests that the enantioselectivity is determined later in the mechanism.Deuterium labeling studies suggest that electron-withdrawing P-aryl substituents increase the rate of reductive elimination of the product nitrile from the (η3-benzyl)nickel cyanide intermediate and, on this basis, a rationale for the ligand electronic effect is proposed.
