Green Halogenation of Indoles with Oxone-Halide.

Oxidative functionalization of indoles is one of the most widely used approaches to exploit the synthetic utility of indoles. In continuation of our research interest in the green oxidation of indoles, we further explore the oxidation of indoles with oxone-halide and discover that the protecting group on the nitrogen of indoles plays a decisive role in controlling the pathways of indole oxidation with oxone-halide. An electron-withdrawing group on the nitrogen of indoles (N-EWG) enables C2 halogenation with stoichiometric halide, while C3 halogenation could be selectively achieved by using stoichiometric halide without dependence on the electronic property of the protecting group on the indole nitrogen. Different from our previous results obtained by using catalytic halide, these findings lead to the development of an environmentally friendly, efficient, and mild protocol for access to 2- or 3-haloindoles (chloro and bromo). As compared to the previous synthetic methods for 2-/3-haloindoles, our method exploits the in situ-generated reactive halogenating species from oxone-halide for halogenation of indoles and thus eliminates the use of stoichiometric halogenating agents and the production of toxic and hazardous organic byproducts derived from oxidants.

Reconfigurable and tunable terahertz wrench-shape metamaterial performing programmable characteristic.

A design of a tunable terahertz (THz) programmable device by using wrench-shape metamaterial (WSM) is presented, which is composed of a Au layer fabricated on a Si substrate. The size of the WSM unit cell is 30 µm×30 µm, and the distance between each WSM is 20 µm. The electromagnetic response of the THz programmable device exhibits the switch function for single-band resonance and dual-band resonance at the transverse electric mode and transverse magnetic mode. The resonance spans from 3.00 to 8.00 THz and is insensitive to the angle of the incident THz wave. While changing the incident angle of the THz wave, the bandwidth of the resonance becomes broader and the transmission spectrum decreases gradually. By configuring the unit cell from single-atom to quad-atom, WSM exhibits optical-logic behaviors with programmable characteristics and anti-interference. Such results are very suitable for use for an ultra-narrowband filter, single-/dual-band switch, polarization switch, and programmable device. It could potentially provide all-optical logical devices with multichannel data processing at higher bit rates.