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Acyclic ketone‐derived oxocarbenium ions are involved as intermediates in numerous reactions that provide valuable products, however, they have thus far eluded efforts aimed at asymmetric catalysis. We report that a readily accessible chiral carboxylic acid catalyst exerts control over asymmetric cyclizations of acyclic ketone‐derived trisubstituted oxocarbenium ions, thereby providing access to highly enantioenriched dihydropyran products containing a tetrasubstituted stereogenic center. The high acidity of the carboxylic acid catalyst, which exceeds that of the well‐known chiral phosphoric acid catalyst TRIP, is largely derived from stabilization of the carboxylate conjugate base through intramolecular anion‐binding to a thiourea site. [ABSTRACT FROM AUTHOR]

In a concentrating photovoltaic (CPV) system, realizing an illumination spot consistent with the photosensitive area of the CPV cell while maintaining high optical performances is a challenging but rewarding issue. For instance, uniform irradiance distribution not only reduces the risk of damage to CPV cells due to the local heat accumulation, but also improves photoelectric conversion efficiency; free chromatic aberration ensures that a wide solar spectrum can be regulated; a high concentration ratio helps reduce the usage of CPV cells, and so on. Here, we propose a method to design a freeform mirror array to concentrate sunlight and generate a square light pattern with uniform irradiance distribution on the photovoltaic cell. Each freeform mirror can produce a uniform illumination pattern on the CPV cell. We demonstrate the effectiveness of the proposed method with several design examples, and a series of factors affecting the optical performance is also analyzed.

The aim of this paper is to develop a new composite structure of catadioptric optical system containing both freeform refractive surface and freeform total internal reflective (TIR) surface for LED road illumination applications. The role of freeform refractive part is to generate the shifted general rectangular illumination pattern to optimally match the shape of the road surface. The application of TIR mechanism is aimed to control the stray light in the sidewalk direction of the road luminaire and maximize the efficient energy efficiency. In this paper, we use the "double pole" ray mapping technique to design the refractive optical surface and the θ-φ coordinate ray mapping technique to derive the freeform TIR surface. The simulation shows that the novel catadioptric design has relatively high collection efficiency, thus high average illuminance level inside the effective illumination area. This lens also has good control of stray light on the backside of the road luminaire.