Allylation Reactions of Aldehydes with Allylboronates in Aqueous Media: Unique Reactivity and Selectivity that are Only Observed in the Presence of Water

Zn(OH)₂‐catalyzed allylation reactions of aldehydes with allylboronates in aqueous media have been developed. In contrast to conventional allylboration reactions of aldehydes in organic solvents, the α‐addition products were obtained exclusively. A catalytic cycle in which the allylzinc species was generated through a B‐to‐Zn exchange process is proposed and kinetic studies were performed. The key intermediate, an allylzinc species, was detected by HRMS (ESI) analysis and by online continuous MS (ESI) analysis. This analysis revealed that, in aqueous media, the allylzinc species competitively reacted with the aldehydes and water. An investigation of the reactivity and selectivity of the allylzinc species by using several typical allylboronates ( 6a , 6b , 6c , 6d ) clarified several important roles of water in this allylation reaction. The allylation reactions of aldehydes with allylboronic acid 2,2‐dimethyl‐1,3‐propanediol esters proceeded smoothly in the presence of catalytic amounts of Zn(OH)₂ and achiral ligand 4d in aqueous media to afford the corresponding syn‐adducts in high yields with high diastereoselectivities. In all cases, the α‐addition products were obtained and a wide substrate scope was tolerated. Furthermore, this reaction was applied to asymmetric catalysis by using chiral ligand 9 . Based on the X‐ray structure of the Zn‐ 9 complex, several nonsymmetrical chiral ligands were also found to be effective. This reaction was further applied to catalytic asymmetric alkylallylation, chloroallylation, and alkoxyallylation processes and the synthetic utility of these reactions has been demonstrated.     

Very fast magic angle spinning (1)H-(14)N 2D solid-state NMR: sub-micro-liter sample data collection in a few minutes

Substantial resolution and sensitivity enhancements of solid-state (1)H detected (14)N HMQC NMR spectra at very fast MAS rates up to 80 kHz, in a 1mm MAS rotor, are presented. Very fast MAS enhances the (1)H transverse relaxation time and efficiently decouples the (1)H-(14)N interactions, both effects leading to resolution enhancement. The micro-coil contributes to the sensitivity increase via strong (14)N rf fields and high sensitivity per unit volume. (1)H-(14)N HMQC 2D spectra of glycine and glycyl-L-alanine at 70 kHz MAS at 11.7 T are observed in a few minutes with a sample volume of 0.8 μL.     

Topotactic Conversion of β‐Helix‐Layered Silicate into AST‐Type Zeolite through Successive Interlayer Modifications

AST‐type zeolite with a plate morphology can be synthesized by topotactic conversion of a layered silicate (β‐helix‐layered silicate; HLS) by using N,N‐dimethylpropionamide (DPA) to control the layer stacking of silicate layers and the subsequent interlayer condensation. Treatment of HLS twice with 1) hydrochloric acid/ethanol and 2) dimethylsulfoxide (DMSO) are needed to remove interlayer hydrated Na ions and tetramethylammonium (TMA) ions in intralayer cup‐like cavities (intracavity TMA ions), both of which are introduced during the preparation of HLS. The utilization of an amide molecule is effective for the control of the stacking sequence of silicate layers. This method could be applicable to various layered silicates that cannot be topotactically converted into three‐dimensional networks by simple interlayer condensation by judicious choice of amide molecules.     

Effect of substrate orientation on the defect-induced bound exciton emissions in GaAs grown by molecular beam epitaxy

The dependence of photoluminescence (PL) spectra at 2 K on the substrate orientation is reported for GaAs grown by molecular beam epitaxy (MBE). Samples investigated are GaAs grown on (n11)A- and (n11)B-oriented substrates where n is 2, 3, 5 and 9, and those on (321)A- (110)B- and (100)A-oriented ones. It was demonstrated that emissions denoted by defect-induced bound excitons (DIBE) present strong crystal orientation dependence. In the (n11) series, DIBE was enhanced peculiarly in (211)A and (311)A substrates and two sharp emissions denoted by t^* and v₃ were specifically observed there, but they were completely quenched for the (211)B substrate. When n exceeds 3, DIBE was observed ubiquitously in (n11)A and (n11)B substrates. The (321)A substrate indicated a most idiosyncratic DIBE with a strong enhancement of t^* and v₃. These results show that the spectral features pertinent to DIBE fully reflect the whole stacking process of impinging molecular beams on the growth front which is governed by the surface structure inherent to the surface dangling bonds of the substrate.     

Effect of surface roughness on the statistical distribution of image speckle intensity

An experimental investigation is made of the effect of surface roughness on the statistical distribution of image speckle intensity. A speckle pattern is formed by spatially coherent light at the image plane of an object having some surface roughness and its statistical properties are investigated. It is found that the contrast of the speckle is related to the surface roughness. By this relation, a new technique for the measurement of surface roughness is proposed.     

Statistical properties of the sum of partially-developed,correlated speckle patterns

General formulas for the average contrast and probability density function of the sum ofN partially-developed, correlated speckle patterns have been theoretically derived. These two parameters characterizing the statistical properties of added speckle patterns have been actually evaluated for the sum of two partially-developed, correlated speckle patterns and shown in figures as a function of the surface roughness of illuminated objects, the wavelength difference of two illuminating lights, and the number of scattering cells within the illuminated area of objects.     

Fibre bundle scanner for laser photocoagulation treatment

Wide-angle irradiation is achieved in laser photocoagulation treatment by means of a fibre bundle. The laser transmission system consists of multiple quartz fibres, the input ends of which are aligned and driven by a stepper motor across a high-power laser beam. The output ends are arranged in a hexagonal close-packed array from which the diverging laser beam successively irradiates different parts of a lesion without the use of a mechanical scan over the lesion. This fibre bundle scanner is useful for the treatment of widely spread skin lesions such as port wine stains.