Reaction of Acetals with Various Carbon Nucleophiles under Non‐Acidic Conditions: C?C Bond Formation via a Pyridinium‐Type Salt

Mild substitution reactions of acetals with carbon nucleophiles via the pyridinium‐type salts generated by the treatment of acetals with TESOTf‐2,4,6‐collidine or 2,2′‐bipyridyl have been developed. Various carbon nucleophiles, such as organocuprates, silyl enol ethers, enamines, etc., reacted with the pyridinium‐type salts to give the corresponding substituted products in good yields. The reactions proceeded under very mild conditions (non‐acidic conditions) and thus acid‐sensitive functional groups can be tolerated during the reaction. In addition, only an acetal can form the pyridinium‐type salt and react with nucleophiles in the presence of a ketal. This unusual selectivity is in contrast to general methods conducted under acidic conditions.     

Double-leaf microperforated panel space absorbers: A revised theory and detailed analysis

A double-leaf microperforated panel space absorber (DLMPP) is composed of two microperforated panels (MPPs) placed in parallel with an air-cavity in-between, without a back wall or any backing structure. This was proposed as a space sound absorber, which can be used for a sound absorbing screen or partition. A conventional MPP absorber with a rigid back wall is effective only around its resonance frequency, which is usually at middle frequencies, and not effective at low frequencies. However, a DLMPP can be effective also at low frequencies, because an additional sound absorption is produced by its acoustic flow resistance. In the authors’ previous work, theoretical analyses on the acoustic properties of a DLMPP were carried out using a simplified electro-acoustical equivalent circuit model. However, the equivalent circuit model includes an approximation, and more sophisticated theory is required for a better prediction and detailed discussion. In this paper, a revised theory for a DLMPP is presented: A Helmholtz integral formulation is employed to obtain a rigorous solution for more precise prediction of the absorptivity of a DLMPP. The result of the present revised theory is compared with that of the equivalent circuit model, and the difference between them is discussed. A parametric survey is made through numerical examples by the present revised theory to discuss its acoustic properties.     

Chemical modification of poly(vinyl chloride) by nucleophilic substitution

The reaction of poly(vinyl chloride) (PVC) in nucleophile (Nu)/ethylene glycol (EG) or Nu/N,N-dimethylformamide (DMF) solution was found to result in the substitution of Cl in PVC with Nu from solution, in addition to the straight elimination of HCl, both of which led to the dechlorination of PVC. Examined Nu⁻ were I⁻, SCN⁻, OH⁻, N₃⁻, and the phthalimide anion. For the Nu/EG solution, elimination was favoured over substitution for all Nu⁻. The ratio of substitution to dechlorination was notable, descending in the order OH⁻ > SCN⁻ = N₃⁻ > phthalimide anion > I⁻. For the Nu/DMF solution, the ratio of substitution to dechlorination was high, in the order SCN⁻ > N₃⁻ > I⁻ > phthalimide anion. In both cases, the orders of the ratios were similar to those of the nucleophilic reactivity constant, I⁻ > SCN⁻ > N₃⁻ > phthalimide anion, except for I⁻. The low ratio for I⁻ was attributable to the elimination of HI after the substitution of Cl in PVC with I in solution, because I⁻ is a strong nucleophile, as well as an excellent leaving group. Comparing the effect of EG and DMF on the substitution of Cl in PVC with Nu in solution, the ratio of substitution to dechlorination was higher for I⁻, SCN⁻, N₃⁻, and the phthalimide anion in DMF than in EG. The substitution of Cl in PVC with Nu in solution was found to occur preferentially in DMF versus EG.     

Application of atomic stereomicroscope to surface science

A stereograph of atomic arrangement was displayed directly on the screen of display-type spherical-mirror analyzer without any computer-aided conversion process for the first time. This stereoscopic photograph enables viewing three-dimensional atomic arrangement. This technique was realized taking advantage of the phenomenon of circular dichroism in photoelectron angular distribution. The azimuthal shifts of forward focusing peaks in a photoelectron angular distribution taken with left and right helicity light in a special arrangement are the same as the parallaxes in a stereo view of atoms. Hence a stereoscopic recognition of three-dimensional atomic arrangement is possible, when the left eye and the right eye respectively view the two images obtained by left and right helicity light simultaneously.     

Simple construction of bicyclo[4.3.0]nonane,bicyclo[3.3.0]octane,and related benzo derivatives by palladium-catalyzed cycloalkenylation

[reaction: see text] Bicyclo[4.3.0]nonanes (hydrindanes) and bicyclo[3.3.0]octanes (octahydropentalenes) are easily synthesized by palladium-catalyzed cycloalkenylations. Additionally, benzo-fused bicyclo[3.3.0]octanes are prepared for the first time through intramolecular coupling between silyl enol ethers and aromatic rings in the presence of catalytic palladium acetate.     

Highly enantioselective phase-transfer-catalyzed alkylation of protected alpha-amino acid amides toward practical asymmetric synthesis of vicinal diamines, alpha-amino ketones, and alpha-amino alcohols

Highly enantioselective alkylation of protected glycine diphenylmethyl (Dpm) amide 1 and Weinreb amide 10 has been realized under phase-transfer conditions by the successful utilization of designer chiral quaternary ammonium salts of type 4 as catalyst. Particularly, remarkable reactivity of the chiral ammonium enolate derived from 1b and 4c allowed the reaction with less reactive simple secondary alkyl halides with high efficiency and enantioselectivity. An additional unique feature of this chiral ammonium enolate is its ability to recognize the chirality of beta-branched primary alkyl halides, which provides impressive levels of kinetic resolution and double stereodifferentiation during the alkylation, allowing for two alpha- and gamma-stereocenters to be controlled. Combined with the subsequent reduction using LiAlH4 in cyclopentyl methyl ether (CPME), this system offers a facile access to structurally diverse optically active vicinal diamines. Furthermore, the optically active alpha-amino acid Weinreb amide 11 can be efficiently converted to the corresponding amino ketone by a simple treatment with Grignard reagents. In addition, reduction and alkylation of the optically active alpha-amino ketone into both syn and anti alpha-amino alcohols with almost complete relative and absolute stereochemical control have been achieved. With (S,S)- and (R,R)-4 in hand, the present approach renders both enantiomers of alpha-amino amides including Weinreb amides readily available with enormous structural variation and also establishes a general and practical route to vicinal diamines, alpha-amino ketones, and alpha-amino alcohols with the desired stereochemistry.     

Metamagnetic quantum criticality revealed by 17O-NMR in the itinerant metamagnet Sr3Ru2O7

We have investigated the spin dynamics using 17O-NMR in the bilayered perovskite Sr3Ru2O7, which sits close to a metamagnetic quantum critical point. The nuclear spin-lattice relaxation rate divided by temperature 1/T1T is enhanced on approaching the metamagnetic critical field of approximately 7.9 T, and at the critical field 1/T1T continues to increase and does not show Fermi-liquid behavior down to 0.3 K. The temperature dependence of T1T in this region suggests the critical temperature Theta to be approximately 0 K, which is strong evidence that the spin dynamics possesses a quantum critical character. Comparison between uniform susceptibility and 1/T1T reveals that antiferromagnetic fluctuations instead of two-dimensional ferromagnetic fluctuations dominate the spin fluctuation spectrum at the critical field, which is unexpected for itinerant metamagnetism.     

A photo-reagent system of benzimidazoline and Ru(bpy)3Cl2 to promote hexenyl radical cyclization and Dowd–Beckwith ring-expansion of α-halomethyl-substituted benzocyclic 1-alkanones

A combination of 2-aryl substituted 1,3-dimethyl-benzimidazolines (DMBIHs) and tris(2,2′-bipyridine)ruthenium(II) chloride, Ru(bpy)₃Cl₂ was used to promote photoinduced electron-transfer (PET) reactions of α-halomethyl-substituted benzocyclic 1-alkanones. This photo-reagent system stimulates free radical forming, cleavage of both carbon–bromine and carbon–chlorine bonds that are not activated by carbonyl groups. The resulting free radicals undergo 5-exo hexenyl cyclization as well as sequential cyclization and ring-expansion (Dowd–Beckwith) reactions to form radicals that abstract hydrogen atoms from the radical cation of DMBIH to yield the observed products. The results of a study of the effects of substituents located on the 2-aryl ring of DMBIH suggest that steric and hydrogen-bonding interactions influence the nature of the reaction pathways followed by the radical intermediates. PET reactions using an iridium complex and DMBIH were also investigated.     

Synthesis of Hydrotalcite from Seawater and Its Application to Phosphorus Removal

10.0 wt% milk of lime was added to seawater containing AlCl 3 at Mg/Al molar ratio of 3.0 until pH 10.5 with stirring, and kept at 25;C for 1 h. Hydrotalcite (HT) was precipitated as a single phase, and Mg 2+ and Al 3+ were quantitatively precipitated. The chemical composition was [Mg 0.75 Al 0.25 (OH) 2 ][(SO 4 ) 0.06 (Cl) 0.02 (OH) 0.11 *];0.27H 2 O* (*Balance). A 100 mg-P/L Na 2 HPO 4 solution and the HT were shaken at 25;C. Phosphate removal increased with increasing time and the HT quantity, and was the highest at pH 7-9. Phosphate ion could be quantitatively removed, adding 8 times the stoichiometric quantity of the HT at pH 8.7 for 6 h.