There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Efficient and reliable amplification of chirality has borne its greatest fruit with transition metal-catalyzed reactions since enantiocontrol may often be imposed by replacing an achiral or chiral racemic ligand with one that is chiral and scalemic While the most thoroughly developed enantioselective transition metal-catalyzed reactions are those involving transfer of oxygen (epoxidation and dihydroxylation)1,2 and molecular hydrogen,3 the focus of this review is on the area of enantioselective transition metal-catalyzed allylic alkylations which may involve C-C as well as C-X (X ) H or heteroatom) bond formation4-9 The synthetic utility of transitionmetal-catalyzed allylic alkylations has been soundly demonstrated since its introduction nearly three decades ago10-21 In contrast to processes where the allyl moiety acts as the nucleophilic partner, we will limit our discussion to processes which result in nucleophilic displacements on allylic substrates (eq 1) Such reactions have been recorded with a broad

http://web4.uwindsor.ca/users/j/jlichaa/reference.nsf/0/10ff8b04ff3a317885256d88005720f6/$FILE/cr-1996-96-395-allylpd-asym.pdf

Asymmetric Transition Metal-Catalyzed Allylic Alkylations.

The increasing demand to produce enantiomerically pure pharmaceuticals, agrochemicals, flavors, and other fine chemicals has advanced the field of asymmetric catalytic technologies.1,2 Among all asymmetric catalytic methods, asymmetric hydrogenation utilizing molecular hydrogen to reduce prochiral olefins, ketones, and imines, have become one of the most efficient methods for constructing chiral compounds.3 The development of homogeneous asymmetric hydrogenation was initiated by Knowles4a and Horner4b in the late 1960s, after the discovery of Wilkinson’s homogeneous hydrogenation catalyst [RhCl(PPh3)3]. By replacing triphenylphosphine of the Wilkinson’s catalystwithresolvedchiralmonophosphines,6Knowles and Horner reported the earliest examples of enantioselective hydrogenation, albeit with poor enantioselectivity. Further exploration by Knowles with an improved monophosphine CAMP provided 88% ee in hydrogenation of dehydroamino acids.7 Later, two breakthroughs were made in asymmetric hydrogenation by Kagan and Knowles, respectively. Kagan reported the first bisphosphine ligand, DIOP, for Rhcatalyzed asymmetric hydrogenation.8 The successful application of DIOP resulted in several significant directions for ligand design in asymmetric hydrogenation. Chelating bisphosphorus ligands could lead to superior enantioselectivity compared to monodentate phosphines. Additionally, P-chiral phosphorus ligands were not necessary for achieving high enantioselectivity, and ligands with backbone chirality could also provide excellent ee’s in asymmetric hydrogenation. Furthermore, C2 symmetry was an important structural feature for developing new efficient chiral ligands. Kagan’s seminal work immediately led to the rapid development of chiral bisphosphorus ligands. Knowles made his significant discovery of a C2-symmetric chelating bisphosphine ligand, DIPAMP.9 Due to its high catalytic efficiency in Rh-catalyzed asymmetric hydrogenation of dehydroamino acids, DIPAMP was quickly employed in the industrial production of L-DOPA.10 The success of practical synthesis of L-DOPA via asymmetric hydrogenation constituted a milestone work and for this work Knowles was awarded the Nobel Prize in 2001.3k This work has enlightened chemists to realize * Corresponding author. 3029 Chem. Rev. 2003, 103, 3029−3069

New Chiral Phosphorus Ligands for Enantioselective Hydrogenation

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

The Golden Age of Transfer Hydrogenation

Optically active 1,3-O-disubstituted glycerols were obtained by enantioselective homogeneous hydrogenation of the corresponding 1,3-O-disubstituted 1,3-dihydroxypropan-2-ones with different RuII-binap complexes. The highest enantioselectivities were obtained with dimeric chloro-ruthenium complexes on the substrates bearing bulky trityloxy groups.

Ruthenium‐Catalyzed Enantioselective Hydrogenation of 1,3‐O‐Disubstituted 1,3‐Dihydroxypropan‐2‐ones

A simple procedure for the preparation of [(S)Ru(η-C5H5){(S)dpompyr-PP′}H][dpompyr =N-diphenylphosphino-2-(diphenylphosphinoxymethyl)pyrrolidine] from [Ru3(CO)12] is described. The hydride reacts stereospecifically with chloroform or carbon tetrachloride to give [(S)Ru(η-C5H5){(S)dpompyr-PP′}Cl] whose structure is reported. The crystals are monoclinic, space group P21 with a= 11.076(2), b= 10.908(2), c= 12.825(3)A, β= 92.26(2), and Z= 2. The structure was solved by the heavy-atom method and refined to R= 0.0322 using 2 306 diffractometer data with I > 3σ(I). Synthesis of this chloro-complex from [Ru(η-C5H5)(PPh3)2Cl] and (S)dpompyr proceeds with only modest diastereoselectivity whereas reduction of [(S)Ru(η-C5H5){(S)dpompyr-PP′}Cl] using LiAlH4 regenerates 88%[(S)Ru(η-C5H5){(S)dpompyr-PP′}H]. Mechanisms are proposed to explain the observed diastereoselectivities. Circular dichroism and 1H, 13C, and 31P n.m.r. spectra of all new compounds are also reported.

Synthesis and stereochemical studies of the chiral ruthenium complexes [Ru(η-C5H5){(S)dpompyr-PP′}X][dpompyr =N-diphenylphosphino-2-(diphenylphosphinoxymethyl)pyrrolidine, X = H or Cl]. Crystal structure of [(S)Ru(η-C5H5){(S)dpompyr-PP′}Cl]

Sakurai and Mukaiyama aldol reactions have been studied using (tetraMeBITIOP)silver(I) and (BITIANP)silver(I) complexes as catalysts; these complexes show high and comparable activities despite the differences in the electron availability and Lewis acid character of the phosphorus atoms.

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Enantioselective Mukaiyama aldol and Sakurai allylation reactions catalysed by silver(I) complexes with chiral atropisomeric chelating ligands

2,2′,5,5′-Tetramethyl-4,4′-bis(diphenylphosphino)-3,3′-bithiophene: A New, Very Efficient, Easily Accessible, Chiral Biheteroaromatic Ligand for Homogeneous Stereoselective Catalysis.

An efficient and convenient route for the preparation of natural and unnatural histidine by asymmetric hydrogenation with rhodium–phosphine complexes is described. The reductions were performed in the presence of HBF 4 to generate an essential imidazolyl cation. Stereoselective incorporation of D 2 in the α,β-positions was obtained by catalytic deuteration in the presence of MeOD.

Edoardo Cesarotti

Papers

Ruthenium‐Catalyzed Enantioselective Hydrogenation of 1,3‐O‐Disubstituted 1,3‐Dihydroxypropan‐2‐ones

Synthesis and stereochemical studies of the chiral ruthenium complexes [Ru(η-C5H5){(S)dpompyr-PP′}X][dpompyr =N-diphenylphosphino-2-(diphenylphosphinoxymethyl)pyrrolidine, X = H or Cl]. Crystal structure of [(S)Ru(η-C5H5){(S)dpompyr-PP′}Cl]

Enantioselective Mukaiyama aldol and Sakurai allylation reactions catalysed by silver(I) complexes with chiral atropisomeric chelating ligands

2,2′,5,5′-Tetramethyl-4,4′-bis(diphenylphosphino)-3,3′-bithiophene: A New, Very Efficient, Easily Accessible, Chiral Biheteroaromatic Ligand for Homogeneous Stereoselective Catalysis.

Histidine and deuterium labelled histidine by asymmetric catalytic reduction with gaseous H2 or D2; the role of strong non-coordinating acids