Asymmetric Synthesis of Highly Substituted β‐Lactones through Oxidative Carbene Catalysis with LiCl as Cooperative Lewis Acid

The reaction of enals with β‐diketones, β‐ketoesters, and malonates bearing a β‐oxyalkyl substituent at the α‐position by oxidative NHC catalysis to provide highly substituted β‐lactones is described. Reactions occur with excellent diastereo‐ and enantioselectivity. The organo cascade comprises two C? C bond formations and one C? O bond formation. Up to four contiguous stereogenic centers including two fully substituted stereocenters are formed in the cascade.     

Metal–Ligand Cooperation on a Diruthenium Platform: Selective Imine Formation through Acceptorless Dehydrogenative Coupling of Alcohols with Amines

Metal?metal singly‐bonded diruthenium complexes, bridged by naphthyridine‐functionalized N‐heterocyclic carbene (NHC) ligands featuring a hydroxy appendage on the naphthyridine unit, are obtained in a single‐pot reaction of [Ru₂(CH₃COO)₂(CO)₄] with 1‐benzyl‐3‐(5,7‐dimethyl‐1,8‐naphthyrid‐2‐yl)imidazolium bromide (BIN ? HBr) or 1‐isopropyl‐3‐(5,7‐dimethyl‐1,8‐naphthyrid‐2‐yl)imidazolium bromide (PIN ? HBr), TlBF₄, and substituted benzaldehyde containing an electron‐withdrawing group. The modified NHC‐naphthyridine‐hydroxy ligand spans the diruthenium unit in which the NHC carbon and hydroxy oxygen occupy the axial sites. All the synthesized compounds catalyze acceptorless dehydrogenation of alcohols to the corresponding aldehydes in the presence of a catalytic amount of weak base 1,4‐diazabicyclo[2.2.2]octane (DABCO). Further, acceptorless dehydrogenative coupling (ADHC) of the alcohol with amines affords the corresponding imine as the sole product. The substrate scope is examined with 1 (BIN, p‐nitrobenzaldehyde). A similar complex [Ru₂(CO)₄(CH₃COO)(3‐PhBIN)][Br], that is devoid of a hydroxy arm, is significantly less effective for the same reaction. Neutral complex 1 a , obtained by deprotonation of the hydroxy arm in 1 , is found to be active for the ADHC of alcohols and amines under base‐free conditions. A combination of control experiments, deuterium labeling, kinetic Hammett studies, and DFT calculations support metal–hydroxyl/hydroxide and metal–metal cooperation for alcohol activation and dehydrogenation. The bridging acetate plays a crucial role in allowing β‐hydride elimination to occur. The ligand architecture on the diruthenium core causes rapid aldehyde extrusion from the metal coordination sphere, which is responsible for exclusive imine formation.     

Three-Component Coupling Synthesis of Diversely Substituted N-Aryl Pyrroles Catalyzed by Iron(III) Chloride

An efficient and operationally simple three-component coupling synthesis of varieties of N-aryl substituted pyrroles is described in the presence of sustainable and environmentally benign metal catalyst, FeCl₃. This method provides a straightforward approach for the synthesis of N-aryl substituted pyrroles in good yields from easily accessible starting materials such as nitroalkenes, 1,3-dicarbonyl compounds, and primary aromatic amines. The reaction proceeds through a catalytic sequence of Fe(III)-catalyzed amination/Michael/cycloisomerization reactions.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

Theoretical study of XCN− (XF,Cl) anions

Geometrical parameters, vibrational frequencies, zero‐point energy, dipole moment, NBO atomic charges of FCN^?, ClCN^? and their isomers, and the isomerization energy of FCN^? and ClCN^? are studied in detail using the ab initio MP2, CCSD, CCSD(T), and density functional B3LYP methods. The results are compared with the existing data reported using various theoretical methods in conjunction with different basis sets. The effect of electron correlation on the structural properties of these molecular anions is discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Spectral shaping filter for broadband amplifiers

We present the design and implementation of a high-damage threshold spectral shaping filter that can be used to counteract gain narrowing in broadband laser amplifier systems. In contrast to earlier approaches to this problem, the filter has a wide range of tunability in both reflectivity and center wavelength. The shape of the reflectivity curve enables the production of an apodized output spectrum with a clean transform limit. We demonstrate the use of this filter in both regenerative and multipass Ti:Sapphire amplifier systems, yielding super-Gaussian amplified spectra of 70-80 nm width.     

Robust high-quality HfN-HfO/sub 2/ gate stack for advanced MOS device applications

In this letter, a thermally stable and high-quality HfN-HfO/sub 2/ gate stack for advanced MOS applications is reported for the first time. Negligible changes in both equivalent oxide thickness (EOT) and work function of HfN-HfO/sub 2/ gate stack are demonstrated even after 1000/spl deg/C postmetal annealing (PMA), which is attributed to the superior oxygen diffusion barrier property of HfN as well as the thermal stability of the HfN-HfO/sub 2/ interface. Therefore, even without surface nitridation prior to HfO/sub 2/ deposition, the EOT of HfN-HfO/sub 2/ gate stack can be successfully scaled down to less than 10 /spl Aring/ after 1000/spl deg/C PMA with excellent leakage and long-term reliability.     

Cooling of a composite slab in a two-fluid medium

A mixed boundary value problem associated with the diffusion equation that involves the physical problem of cooling of an infinite parallel-sided composite slab in a two-fluid medium, is solved completely by using the Wiener-Hopf technique. An analytical solution is derived for the temperature distribution at the quench fronts being created by two different layers of cold fluids having different cooling abilities moving on the upper surface of the slab at constant speedv. Simple expressions are derived for the values of the sputtering temperatures of the slab at the points of contact with the respective layers, assuming the front layer of the fluid to be of finite width and the back layer of infinite extent. The main problem is solved through a three-part Wiener-Hopf problem of a special type and the numerical results under certain special circumstances are obtained and presented in the form of a table.     

Substitution of aqua ligands from cis‐[Pt(en)(H2O)2](ClO4)2 and cis‐[Pt(dmen)(H2O)2](ClO4)2 (en = ethylenediamine,dmen = N N′‐dimethyl ethylenediamine) by glycine in aqueous medium—a kinetic and mechanistic approach

The kinetics of the interaction of glycine with cis‐[Pt(en)(H₂O)₂](ClO₄)₂ and cis‐[Pt(dmen)(H₂O)₂](ClO₄)₂ (en = ethylenediamine, dmen = N,N′‐dimethylethylene‐diamine) have been studied spectrophotometrically as a function of [substrate complex], [glycine], and temperature at a particular pH (4.0) where the substrate complex exists predominantly as the diaqua species and glycine as the zwitterion. The reaction was found to proceed through two consecutive steps. The first step involves the ligand‐assisted anation, while the second step involves chelation when the second aqua ligand is displaced. Rate constants have been evaluated using the Weyh and Hamm method. Activation parameters for both steps have also been calculated using the Eyring equation. The low enthalpy of activation and large negative values of entropy of activation indicate an associative mode of activation for both steps. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 489–495, 2005     

Kinetics of substitution of aqua ligands from cis‐diaqua (ethylenediamine)platinum(II) perchlorate by L‐asparagine in aqueous medium

The kinetics of the interaction of L ‐asparagine with [Pt(ethylenediamine)(H₂O)₂]²⁺ have been studied spectrophotometrically as a function of [Pt(ethylenediamine)(H₂O)₂²⁺], [L ‐asparagine], and temperature at pH 4.0, where the substrate complex exists predominantly as the diaqua species and L ‐asparagine as the zwitterion. The substitution reaction shows two consecutive steps: the first step is the ligand‐assisted anation and the second one is the chelation step. Activation parameters for both the steps have been calculated using Eyring equation. The low ΔH₁^≠ (43.59 ± 0.96 kJ mol^?1) and large negative values of ΔS₁^≠ (?116.98 ± 2.9 J K^?1 mol^?1) as well as ΔH₂^≠ (33.78 ± 0.51 kJ mol^?1) and ΔS₂^≠ (?221.43 ± 1.57 J K^?1 mol^?1) indicate an associative mode of activation for both the aqua ligand substitution processes. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 252–259, 2003     

Conformational relaxation in the excited electronic states of benzil and naphthyl

A time-resolved study of the emission from benzil and naphthyl in semi-solid glasses (e.g. alcoholic glass near the melting point) using a pulsed N₂-laser as an excitation source is reported. The emission from the relaxed excited triplet shows a growth followed by a decay. This growth provides a convincing proof of geometrical relaxation occurring in the excited states of benzil and naphthyl.