Catalytic asymmetric synthesis of unsymmetrical triarylmethanes with a chiral all-carbon quaternary center was achieved by using a chiral bifunctional quaternary phosphonium bromide catalyst in the S(N)Ar reaction of 3-aryloxindoles under phase-transfer conditions. The presence of a urea moiety in the chiral phase-transfer catalyst was important for obtaining high enantioselectivity in this reaction.
A large-diameter uniform plasma is obtained by microwave discharge without the use of magnetic fields at pressures in the mTorr range. Microwave fields at 2.45 GHz are radiated from a multislotted planar antenna located a short distance above the glass window of a discharge chamber. Overdense plasmas are produced with ± 3-4% uniformity of ion saturation current over 30 cm diameter for wide ranges of microwave power and gas pressure. The discharge can be started up at pressures as low as 0.5 mTorr. The efficient production of overdense plasmas is investigated by measuring microwave field propagation in the system.
It is reported that a large-diameter uniform plasma is obtained by microwave discharges using multi-slotted planar (MSP) antenna. The MSP antenna radiates the microwave field from a large number of slots so as to form a uniform radial distribution of the field in the outer radii. Overdense plasmas are produced with ±3-4% uniformity of the ion saturation current over a 30 cm diameter for Ar pressures of 5-10 mTorr and microwave powers of 1-3 kW. The efficient production of overdense plasmas may be due to the enhancement of the microwave field of oblique incidence at the plasma resonance.
Catalytic asymmetric synthesis of unsymmetrical triarylmethanes with a chiral all‐carbon quaternary center was achieved by using a chiral bifunctional quaternary phosphonium bromide catalyst in the SNAr reaction of 3‐aryloxindoles under phase‐transfer conditions. The presence of a urea moiety in the chiral phase‐transfer catalyst was important for obtaining high enantioselectivity in this reaction.
Planar microwave discharges using a multi-slotted planar antenna are investigated. The enhancement of the microwave fields near the plasma resonance is observed in accordance with the theory of the resonant absorption. By operating the antenna with the azimuthally rotating fields, highly uniform overdense plasmas can be produced without being affected by eigenmode structures of surface waves. As a result, the radial distribution of the ion saturation current can be controlled by tailoring the power radiation profile from the antenna. It is also demonstrated that the active control of the plasma uniformity is possible by simply changing the vertical position of the antenna.
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