exo-selective asymmetric Diels-Alder reaction catalyzed by diamine salts as organocatalysts

[reaction: see text] A novel binaphthyl-based diamine (R)-2 was designed and synthesized. A protonic acid-(R)-2 salt catalyst has the advantage of exhibiting unprecedented high exo selectivity in the asymmetric Diels-Alder reaction of alpha,beta-unsaturated aldehydes. For instance, the reaction between cinnamaldehyde and cyclopentadiene in the presence of 12 mol % of binaphthyl-based diamine (R)-2 and 10 mol % of p-TsOH.H(2)O in alpha,alpha,alpha-trifluorotoluene at -20 degrees C gave the corresponding exo cycloadduct with 92% ee as a major diastereomer (exo/endo = 13/1).     

Palladium-catalyzed decarboxylative coupling of benzoic acid derivatives using hydrazone ligands

Palladium-catalyzed decarboxylative coupling of benzoic acid derivatives with arylboroxins gave biaryls using a catalytic amount of Pd(TFA)₂–hydrazone 1d system with Ag₂CO₃ at 80 °C in good yields. We also found that decarboxylative coupling with aryl(trialkoxy)silanes gave biaryls using a Pd(TFA)₂–hydrazone 1g system with AgF in good yields.     

Chemical synthesis of human adiponectin(19–107) bearing post-translational glycosylation

Human adiponectin(19–107), which consists of the variable region and the collagenous domain bearing post-translational modifications including glycosylation, was chemically synthesized for the first time. A glycoside of 5-hydroxylysine (Hyl) was incorporated using an α-d-glucopyranosyl-(1→2)-β-d-galactopyranosyl/Hyl-Gly building block in a benzyl-protected form by solid-phase peptide synthesis (SPPS). The molecule was assembled from four segments prepared by SPPS via native chemical ligation (NCL) and thioester methods.     

Construction of Quaternary Carbon Center by Catalytic Asymmetric Alkylation of 3‐Arylpiperidin‐2‐ones Under Phase‐Transfer Conditions

A highly enantioselective synthesis of δ‐lactams having a chiral quaternary carbon center at the α‐position has been developed through an asymmetric alkylation of 3‐arylpiperidin‐2‐ones under phase‐transfer conditions. In this transformation, a 2,2‐diarylvinyl group on the δ‐lactam nitrogen atom plays a crucial role as a novel protecting group and an achiral auxiliary for improving both yield and enantioselectivity of the reaction.     

exo‐Selective Asymmetric Diels–Alder Reaction Catalyzed by Diamine Salts as Organocatalysts

An organocatalyst formed from a binaphthyl‐substituted diamine and trifluoromethanesulfonic acid exhibited unprecedented levels of exo selectivity in the Diels–Alder reaction of α,β‐unsaturated aldehydes with cyclopentadiene. A novel axially chiral diamine was also designed as an organocatalyst for an asymmetric variant of this reaction, in which the desired cycloadducts were formed with high diastereo‐ and enantioselectivities. The highest diastereoselectivity observed was greater than 20:1 in favor of the exo cycloadduct in the asymmetric Diels–Alder reaction of crotonaldehyde with cyclopentadiene.     

The first stereospecific arylation of (Z)‐germyl(stannyl)ethenes with an aryl halide or heteroaryl halide under palladium‐catalysis

A combination catalyst of Pd(dba)₂‐PPh₃‐CuI‐LiCl or Pd(dba)₂‐P(2‐furyl)₃‐CuI‐LiCl effectively catalyzed the cross‐coupling of (Z)‐germyl(stannyl)ethenes with aryl halides, providing novel triethyl(2,2‐diarylethenyl)germanes in good to high yields. The reaction proceeds with retention of configuration. Cross‐coupling results in the formation of phenylene or phenyleneethynylene derivatives with terminal stereochemically defined vinylgermane unit(s). Copyright © 2008 John Wiley & Sons, Ltd.     

Metal-intercalated aromatic hydrocarbons: a new class of carbon-based superconductors

New carbon-based superconductors are synthesized by intercalating metal atoms into the solid-phase hydrocarbons picene and coronene. The highest reported superconducting transition temperature, T(c), of a hydrocarbon superconductor is 18 K for K(3)picene. The physics and chemistry of the hydrocarbon superconductors are extensively described for A(x)picene (A: alkali and alkali earth-metal atoms) for x = 0-5. The theoretical picture of their electronic structure is also reviewed. Future prospects for hydrocarbon superconductors are discussed from the viewpoint of combining electronics with condensed-matter physics: modification of the physical properties of hydrocarbon solids is explored by building them into a field-effect transistor. The features of other carbon-based superconductors are compared to clarify the nature of hydrocarbon superconductors.     

Proton-coupled electron transfer of the phenoxyl/phenol couple: effect of Hartree-Fock exchange on transition structures

Proton-coupled electron transfer (PCET) and hydrogen atom transfer (HAT) reactions of the phenoxyl/phenol couple are studied theoretically by using wave function theory (WFT) as well as DFT methods. At the complete active space self-consistent field (CASSCF) level, geometry optimization is found to give two transition states (TSs); one is the PCET type with two benzene rings being nearly coplanar, and the other is the HAT type with two benzene rings taking a stacking structure. Geometry optimization at the (semilocal) DFT level, on the other hand, is found to give only one transition state (i.e., the PCET-type one) and fail to obtain the stacking TS structure. By comparing various levels of theories (including long-range corrected DFT functionals), we demonstrate that the Hartree-Fock exchange at long range plays a critical role in obtaining the sufficient stacking stabilization of the present open-shell system, and that the sole addition of empirical dispersion correction to semilocal DFT functionals may not be adequate for describing such a stacking interaction. Next, we investigate the solvent effect on the PCET and HAT TS thus obtained using the reference interaction site model self-consistent field (RISM-SCF) method. The results suggest that the free energy barrier increases with increasing polarity of the solvent, and that the solvent effects are stronger for the PCET TS than the stacking HAT TS pathway. The reason for this is discussed based on the dipole moment of different TS structures in solution.