Xanthone natural products via N-heterocyclic carbene catalysis: total synthesis of atroviridin.

The total synthesis of atroviridin has been accomplished by a linear route involving the N-heterocyclic carbene (NHC)-catalyzed aroylation of the fluorobenzene derivative, Claisen cyclization of the O-propargylated benzophenones, and intramolecular 1,4-addition of the quinone intermediates. The result provides a viable route to xanthone natural products.

Strain-induced modulation of temperature characteristics in ferrimagnetic Tb-Fe films.

This study investigates the effect of strain on the compensation temperature of ferrimagnetic Tb-Fe films formed on a flexible substrate. The compensation temperature is determined by the anomalous Hall measurement, and an application of 1.2% tensile strain reduces the compensation temperature by 12 K. X-ray magnetic circular dichroism reveals that approximately 5% of Fe magnetic moment and approximately 1% of Tb magnetic moment are reduced by an application of 0.9% tensile strain at the room temperature. To understand the greater reduction in Fe magnetization compared with that in Tb and the compensation temperature reduction simultaneously, a model applying molecular field theory is analyzed. Changes in three types of exchange coupling between Fe and Tb atoms are speculated to be caused by the strain.

Strain-induced switching of heat current direction generated by magneto-thermoelectric effects.

Since the charge current plays a major role in information processing and Joule heating is inevitable in electronic devices, thermal management, i.e., designing heat flows, is required. Here, we report that strain application can change a direction of a heat current generated by magneto-thermoelectric effects. For demonstration, we used metallic magnets in a thin-film form, wherein the anomalous Ettingshausen effect mainly determines the direction of the heat flow. Strain application can alter the magnetization direction owing to the magnetoelastic effect. As a result, the heat current, which is in the direction of the cross product of the charge current and the magnetization vector, can be switched or rotated simply by applying a tensile strain to the metallic magnets. We demonstrate 180° switching and 90° rotation of the heat currents in an in-plane magnetized Ni sample on a rigid sapphire substrate and a perpendicularly magnetized TbFeCo film on a flexible substrate, respectively. An active thermography technique was used to capture the strain-induced change in the heat current direction. The method presented here provides a novel method for controlling thermal energy in electronic devices.

N-heterocyclic carbene-catalyzed nucleophilic aroylation of fluorobenzenes.

In N-heterocyclic carbene (NHCs) catalyzed nucleophilic substitution of fluorobenzenes, fluoro groups are replaced by aroyl groups, which are derived from aromatic aldehydes. 1,3,4,5-Tetramethylimidazol-2-ylidene is found to be an efficient catalyst. The catalyst loading can be reduced to 1 mol % without a significant decrease in the product yields. Polysubstituted benzophenones are synthesized from fluorobenzenes and benzaldehydes by the NHC-catalyzed aroylation.