Graphite oxide (GO) and its derivatives have been studied using 13C and 1H NMR. NMR spectra of GO derivatives confirm the assignment of the 70 ppm line to C−OH groups and allow us to propose a new structural model for GO. Thus we assign the 60 ppm line to epoxide groups (1,2-ethers) and not to 1,3-ethers, as suggested earlier, and the 130 ppm line to aromatic entities and conjugated double bonds. GO contains two kinds of regions:  aromatic regions with unoxidized benzene rings and regions with aliphatic six-membered rings. The relative size of the two regions depends on the degree of oxidation. The carbon grid is nearly flat; only the carbons attached to OH groups have a slightly distorted tetrahedral configuration, resulting in some wrinkling of the layers. The formation of phenol (or aromatic diol) groups during deoxygenation indicates that the epoxide and the C−OH groups are very close to one another. The distribution of functional groups in every oxidized aromatic ring need not be identical, and both ...

Structure of Graphite Oxide Revisited

Synthetic Principles for Bandgap Control in Linear pi-Conjugated Systems.

2.5. Stabilization of IL Emulsions by Nanoparticles 2623 3. Hydrogenations in ILs 2623 3.1. Hydrogenation on IL-Stabilized Nanoparticles 2623 3.1.1. Hydrogenation of 1,3-Butadiene 2623 3.1.2. Hydrogenation of Alkenes and Arenes 2624 3.1.3. Hydrogenation of Ketones 2624 3.2. Homogeneous Catalytic Hydrogenation in ILs 2624 3.3. Hydrogenation of Functionalized ILs 2625 3.3.1. Selective Hydrogenation of Polymers 2625 3.4. Asymmetric Hydrogenations 2626 3.4.1. Enantioselective Hydrogenation 2626 3.5. Role of the ILs Purity in Hydrogenation Reactions 2628

Catalysis in ionic liquids

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

Asymmetric 1,3-Dipolar Cycloaddition Reactions

The treatment of α,β-unsaturated esters having a ketone function at an appropriate position with either TBDMSOTf in the presence of Et 3 N or TMSI in the presence of (TMS) 2 NH provided, via a tandem intramolecular Michael-aldol reaction sequence, several different types of cyclobutane derivatives. The two reaction conditions were complementary. Tricyclo[4.2.1.03-8]nonanes 34 and 35, tricyclo[5.1.1.0 3,8 ]nonane 40, tricyclo[5.4.0.0 3,7 ]undecane 51, tetracyclo[5.4.0.0 3,7 .0 9,11 ]undecane 45, and the bicyclo[3.2.0]heptanes 36, 57, and 38, which have structures either partially or completely similar to those of endiandric acids A (1a), B (1b), and C (2), trihydroxydecipiadiene (3), lintenone (4), italicene (3), and filifolone (6), were stereoselectively synthesized by the tandem reaction

Synthesis of polycyclic cyclobutane derivatives by tandem intramolecular Michael-aldol reaction under two complementary conditions: TBDMSOTf-Et3N and TMSI-(TMS)2NH

9, and 10 could not be unambiguously assigned by N M R since the isomers were inseparable by chromatography. Only three of the four possible isomers of 12 were isolated. The major isomer of which bears a cis relationship between the isopropyl and phenyl substituents. To illustrate the potential synthetic utility of this approach to tetrahydrofuran synthesis, a short total synthesis of the hop ether 169 was carried out as shown in Scheme I. The required a-alkoxystannane 13 was readily prepared from acetone by a condensation reaction with Bu3SnLila and subsequent protection of the a-hydroxystannane intermediate with chloromethyl methyl ether. Transmetalation of 13 was accomplished in DME" at -78 "C and cuprate formation2b*d proceeded smoothly. The cuprate reagent 14 underwent clean regiospecific addition to cyclopentenone in the presence of trimethylsilyl chloride to afford the silyl enol ether 15 after quenching the reaction mixture with triethylamine. The crude silyl enol ether 15 was obtained in nearly quantitative yield (GC). Without further purification, 15 was treated with titanium tetrachloride in methylene chloride to provide the annelated tetrahydrofuran 11 in 73% overall yield from cyclopentenone. Methenylation, following the procedure of Lombardo,I0 provided the natural product 16 in good yield (91%). In summary, a-alkoxyorganostannanes, by reaction through the derived a-alkoxyorganocuprate, can be considered as a synthetic equivalent to a carbonyl ylide. Highly substituted tetrahydrofurans are generated in good yields from cyclic and acyclic enones. Further studies are in progress to evaluate the use of other acetal protecting groups (other than MOM) in the final closure step.

Bis(.mu.-acetato)(.mu.-oxo)-bis(tris(pyridine)ruthenium(III)) ion: a ruthenium analog of the hemerythrin active center.

Structure of ephedradine A, a hypotensive principle of Ephedra roots

Synthesis, Structure, and Silylene Exchange Reaction of Base-Stabilized Hydrido(silylene)tungsten Complexes and Rearrangement of Hydrosilyl(pyridine)tungsten Complexes to the Base-Stabilized Hydrido(silylene) Complexes via 1,2-Hydrogen Migration

Chemistry of organosilicon compounds. 167. 3,4,7,8-Tetrasilacycloocta-1,5-diyne, 3,6,7-trisilacyclohepta-1,4-diyne and related compounds. New class of cyclic compounds composed of polysilanes and acetylenes

Chizuko Kabuto

Papers

Synthesis of polycyclic cyclobutane derivatives by tandem intramolecular Michael-aldol reaction under two complementary conditions: TBDMSOTf-Et3N and TMSI-(TMS)2NH

Bis(.mu.-acetato)(.mu.-oxo)-bis(tris(pyridine)ruthenium(III)) ion: a ruthenium analog of the hemerythrin active center.

Structure of ephedradine A, a hypotensive principle of Ephedra roots

Synthesis, Structure, and Silylene Exchange Reaction of Base-Stabilized Hydrido(silylene)tungsten Complexes and Rearrangement of Hydrosilyl(pyridine)tungsten Complexes to the Base-Stabilized Hydrido(silylene) Complexes via 1,2-Hydrogen Migration

Chemistry of organosilicon compounds. 167. 3,4,7,8-Tetrasilacycloocta-1,5-diyne, 3,6,7-trisilacyclohepta-1,4-diyne and related compounds. New class of cyclic compounds composed of polysilanes and acetylenes