Accelerated Discovery in Photocatalysis by a Combined Screening Approach Involving MS Tags.

Herein we report on the development of an MS tag screening strategy that accelerates the discovery of photocatalytic reactions. By efficiently combining mechanism- and reaction-based screening dimensions, the respective advantages of each strategy were retained, whereas the drawbacks inherent to each screening approach could be eliminated. Applying this approach led to the discovery of a mild photosensitized decarboxylative hydrazide synthesis from mesoionic sydnones and carboxylic acids as starting materials.

NHC-Organocatalyzed CAr -O Bond Cleavage: Mild Access to 2-Hydroxybenzophenones.

A Truce-Smiles rearrangement of acyl-anion equivalents generated by N-heterocyclic carbene (NHC) catalysis has been achieved. The developed method includes CAr -O, CAr -S, or CAr -N bond cleavage for the formation of a CAr -C bond and enables access to 2-hydroxybenzophenones, an important structural motif that is present in several bioactive natural products. By utilizing this procedure, the alkaloid taxilamine was synthesized in three steps. DFT calculations and control experiments support a classical SN Ar mechanism with a catalyst-bound Meisenheimer-type intermediate. The method features mild reaction conditions, excellent functional-group tolerance, and a broad substrate scope, including various classes of (hetero)arenes.

Holodiagrams in birefringent media.

The modifications to the holodiagram concept to describe free propagation (the extraordinary ray) inside birefringent materials are described. Holodiagrams are graphs showing the loci where the sum or the difference in the optical path from a generic point to two foci is the same. The holodiagrams obtained in this way give the shape of the surfaces that satisfy Fermat's principle, conjugate by reflection of one focus into the other, and represent the interference fringes obtained if both points are coherent sources. The reflection law in birefringent media is investigated in relation to this diagram. One direction for the optical axis is considered: parallel to the line joining the source and the observation point. Quartz-type and calcite-type crystals are studied.