Asymmetric alkylation of carboxyamides by using trans-2,5-disubstituted pyrrolidines as chiral auxiliaries

trans-2,5-Bis(methoxymethyl)- and trans-2,5-bis(methoxymethoxymethyl)pyrrolidines proved to be excellent chiral auxiliaries for the asymmetric alkylation of the corresponding carboxyamide enolates giving good chemical yield and high stereoselectivity (invariably over 95% de), with remarkable flexibility to substrates and reaction conditions.     

Retardation of spontaneous polymerization of formaldehyde by acidic substances

The stability of liquid formaldehyde produced by pyrolysis of α-polyoxymethylene was studied in connection with the presence of impurities in the monomer. Liquid monomer was divided into several fractions by means of the distillation. The stability of each fraction for polymerization is dependent on the order of fraction, that is, the monomer obtained in the early fractions of distillation was much more stable with regard to polymerization than later distillate. Analyses of the monomer fractions indicated that various impurities such as carbon dioxide, water, methanol, and methyl formate were present in the early monomer distillates. From the influence of these impurities on the stability of liquid formaldehyde, it was found that small amounts of carbon dioxide and hydrogen cyanide noticeably depressed the polymerization, and that with acetic acid and maleic anhydride the rate of polymerization decreased with small amounts of these compounds but increased with an excess of additive. On the other hand, the addition of these acidic substances did not affect the molecular weight of the polymer produced. From the fact that the acidic substance retards only the initiation of polymerization, it has been concluded that the spontaneous polymerization of formaldehyde in bulk or in toluene solution is initiated by an anionic species.     

Synthetic studies on β-lactam antibiotics. 18. Convenient,stereocontrolled synthesis of 3-methyl 7α-methoxy-1-oxacephems

Alcohols $\text{4}$ and $\text{8}$, prepared from $\text{3}$, underwent completely stereospecific etherification to give 1-oxacephams $\text{5}$ and $\text{10}$, which were converted into the 1-oxacephem nucleus $\text{1b}$ via $\text{6}$ and $\text{1c}$. Functionalization at C-3′ in $\text{6}$ and $\text{1c}$ was unsuccessful.     

Formation, structure, and reactivities of 1:1 adducts between quadricyclane and (η-cyclopentadienyl)(1,2-diphenyl- or -dimethoxycarbonyl-1,2-ethenedithiolato)rhodium(III)

The rhodiadithiolene complexes [Rh(Cp)(S₂C₂Z₂)] (Z=Ph (1a) and COOMe (1b)) reacted with quadricyclane (Q) to give 1:1 adducts [Rh(Cp)(S₂C₂Z₂) (C₇H₈)] (Z=Ph (2a) and COOMe (2b)) in which Rh and S of the complexes are bridged by C(7) (bridge carbons) and C(5) (edge carbons) of norbornene (C₇H₈), respectively. The structure of the adduct 2a was re-investigated and determined by X-ray structural analysis. The rhodiadithiolene complexes and those adducts showed the catalytic activities for the thermal isomerization from Q to norbornadiene (NBD). Adduct 2a photochemically dissociated to give the original complex 1a and NBD upon irradiation with a high-pressure mercury lamp. Skeletal rearrangements of the hydrocarbon moiety were confirmed in the formation of these adducts and in their photo-dissociation, according to deuterium labeling experiments.     

Preparation of cis-2-aminocyclopropanol: [2+1] cycloaddition reaction of bis(iodozincio)methane with α-ketoimine

A reaction of α-ketoimine with bis(iodozincio)methane gave a cis-2-aminocyclopropanol derivative via [2+1] cycloaddition. The reaction proceeded via a sequential nucleophilic attack of bis(iodozincio)methane to a couple of carbonyl groups in the substrate, which was fixed into s-cis conformation with a couple of zinc atoms in the reagent. The reaction proceeded with high diastereoselectivity.     

Evidence for the self-association of anthocyanins IV. PMR spectroscopic evidence for the vertical stacking of anthocyanin molecules

Vertical stacking structure is proposed for the self-association of anthocyanins on the basis of PMR shift data due to the ring current effect of aromatic nuclei of anthocyanins.     

Electron transfer between cofactors in protein domains linked by a flexible tether

Some key electron-transfer (ET) proteins have domains containing redox cofactors connected by a flexible tether. The relative motion of the domains is essential for reaction because of the strong ET rate dependence on distance. The constrained conformational flexibility produces a kinetic regime intermediate between “unimolecular” and “bimolecular”. We used a simple model for ET coupled to conformational diffusion to explore the structure dependence of the ET kinetics. The model describes the evolution of an initially prepared reduced donor state, and recovers the diffusion and electron tunneling-limited regimes. The restriction of the conformational space imposed by the tether introduces an entropic component to the effective donor–acceptor interaction potential. As such, the tether length may control the transition between the electron tunneling and diffusion-limited regimes.     

Concise syntheses of nonracemic gamma-fluoroalkylated allylic alcohols and amines via an enantiospecific palladium-catalyzed allylic substitution reaction

Alpha-fluoroalkylated allyl mesylates reacted with various carboxylates and amines in the presence of tetrakis(triphenylphosphine)palladium(0) catalyst to give the corresponding gamma-fluoroalkylated (E)-allylic alcohol derivatives and amines, respectively, in excellent yields. In almost all cases, no other regio- and stereoisomers were produced. Application of this palladium-catalyzed allylic substitution reaction to various nonracemic mesylates afforded chiral gamma-fluoroalkylated allylic alcohol derivatives and amines without any loss of enantiomeric excess through the reaction.     

Ultrasonic relaxation studies of solutions of triethylamine and 3,3-diethylpentane in 2-propanol as a function of temperature

Ultrasonic absorption data obtained over the frequency range 5–95 MHz by the pulse method are reported for 3,3-diethylpentane and triethylamine in 2-propanol in the temperature range 0–25°C. Data are also reported for triethylamine as a function of concentration. A relaxation is observed under all experimental conditions and is associated with the equilibrium between rotational isomers as previously proposed by other workers. The energy parameters associated with a two-state model for the isomers are evaluated and compared with previous results for the pure liquids. The difference in these parameters for the compounds dissolved in 2-propanol is partly attributed to the difference in the dynamics of rotation of an ethyl group about a carbon-carbon and carbon-nitrogen bond.     

Sound absorption studies of ternary systems

The peak sound absorption region of ternary systems of water-2-propanolurea, water-2-propanol-tetraethylammonium bromide, water-2-propanol-1,10-bis(triethylammonium)decane dibromide, and the binary system water-2-propanol has been studied at 10, 30, and 50 MHz, and in the temperature range 1.4 to 35°C. The results from the binary system show that the peak sound absorption composition (PSAC) is shifted to higher alcohol composition and (/f ²)_max decreases with increasing temperature. At constant frequency, increased urea concentration has the same effect on PSAC and (/f ²)_max values as does an increase in temperature for the binary system. All salts decrease /f ² values at low concentrations but differ remarkably at higher concentrations. The results are interpreted qualitatively as showing the excess sound absorption in the PSAC region to be intimately related to the structural characteristics of water.