A catalytic asymmetric decarboxylative [4+2] cycloaddition of vinyl benzoxazinanones with methyleneindolinones has been established, which provided a series of chiral tetrahydroquinoline-based 3,3'-spirooxindoles in high yields (up to 96%) and with excellent diastereo- and enantioselectivities (all >95 : 5 d.r., up to 99% ee). This reaction not only represents the first example of catalytic enantioselective [4+2] cycloaddition between methyleneindolinones and Pd-containing 1,4-dipoles, but also demonstrates the great practicability of catalytic asymmetric decarboxylative cycloadditions in the synthesis of enantio-enriched polycyclic compounds.
Delta-Phase behaviour has important effect on mechanical properties in Alloy718. Structure control on a-phase behaviour by forging and followed heat treatment processing has been conducted in this research, simultaneously different quantity, morphology and distribution of b-phase have been achieved in turbine disk fabrication. Experimental results indicate that 6-phase behaviour has obvious influence on crack propagation. In certain range a-phase has retardation effect on crack propagation. Crack propagation mechanism and failure analyses under creep and fatigue conditions have been discussed also.
The discharge characteristics and discharge gap of machining Ti-6Al-4V titanium alloy by cryogenically cooled tool electrode electrical discharge machining (EDM) in distilled water were investigated in this study using the monopulse discharge method. The influence of the cryogenically cooled tool electrode on the discharge gap and the initial maintaining voltage between the electrode and workpiece were analyzed under various temperatures. Test results showed the initial maintaining voltage of the cryogenically cooled tool electrode EDM was lower than that of conventional EDM. The discharge gap of the cryogenically cooled tool electrode EDM was also smaller than that of conventional EDM, which improved the copying accuracy of die-sinking EDM. A comparative experiment of machining Ti-6Al-4V titanium alloy was carried out by using cryogenically cooled tool electrode EDM and conventional EDM, lower electrode wear, higher material removal ratio, and higher corner size machining accuracy was obtained by using cryogenically cooled tool electrode EDM.
We report a highly practical copper(II)/TEMPO-SO 4 H catalyst system for aerobic oxidations of primary benzylic and allylic alcohols. A higher activity was achieved when TEMPO-SO 4 H, an economically feasible 2,2,6,6tetramethylpiperidinyl-1-oxyl (TEMPO) derivative containing a sulfonic acid group, was used to replace TEMPO. The use of such Cu II /TEMPO-SO 4 H catalysts can significantly simplify the removal of catalysts and dramatically reduce the amount of organic solvents used. The aerobic oxidation of primary benzylic and allylic alcohols was conducted in water on gram scale using air as the oxidant, and in the absence of surfactant, leading to green catalysis.
Freeform surfaces have become increasingly widespread in the optical systems for enhanced performance and compact lightweight packaging. The geometrical complexity and high precision requirements of optical freeform surfaces for various functional optical applications, has posed great challenges in the design, precision machining, and measurement of these surfaces. This paper presents a model-based self-optimization approach for precision machining and measurement of optical freeform surfaces in the computer controlled bonnet polishing (CCBP) process. To realize the technical feasibility, the process parameters and motion control are accurately performed through modelling and simulation of machining processes, error compensation, and on-machine metrology.
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