Entropic Path Sampling: Computational Protocol to Evaluate Entropic Profile along a Reaction Path.

Fleeting intermediates constitute dynamically stepwise mechanisms. They have been characterized in molecular dynamics trajectories, but whether these intermediates form a free energy minimum to become entropic intermediates remains elusively defined. We developed a computational protocol known as entropic path sampling to evaluate the entropic variation of reacting species along a reaction path based on an ensemble of trajectories.

Migratory Aptitudes in Rearrangements of Destabilized Vinyl Cations.

The Lewis acid-promoted generation of destabilized vinyl cations from β-hydroxy diazo ketones leads to an energetically favorable 1,2-shift across the alkene followed by an irreversible C-H insertion to give cyclopentenone products. This reaction sequence overcomes typical challenges of counter-ion trapping and rearrangement reversibility of vinyl cations and has been used to study the migratory aptitudes of nonequivalent substituents in an uncommon C(sp) to C(sp) vinyl cation rearrangement. The migratory aptitude trends were consistent with those observed in other cationic rearrangements; the substituent that can best stabilize a cation more readily migrates.

Synthesis of Biaryls via Decarbonylative Palladium-Catalyzed Suzuki-Miyaura Cross-Coupling of Carboxylic Acids.

The biaryl motif is a building block in many drugs, agrochemicals, and materials, and as such it is highly desirable as a synthesis target. The state-of-the-art process for biaryl synthesis from ubiquitous carboxylic acids is decarboxylative cross-coupling involving loss of carbon dioxide (CO). However, the scope of these methods is severely limited, mainly due to specific substitution required to promote decarboxylation.

Highly-chemoselective step-down reduction of carboxylic acids to aromatic hydrocarbons palladium catalysis.

Aryl carboxylic acids are among the most abundant substrates in chemical synthesis and represent a perfect example of a traceless directing group that is central to many processes in the preparation of pharmaceuticals, natural products and polymers. Herein, we describe a highly selective method for the direct step-down reduction of carboxylic acids to arenes, proceeding well-defined Pd(0)/(ii) catalytic cycle. The method shows a remarkably broad substrate scope, enabling to direct the classical acyl reduction towards selective decarbonylation by a redox-neutral mechanism.

Self-powered, ultrafast, visible-blind UV detection and optical logical operation based on ZnO/GaN nanoscale p-n junctions.

Ultrafast-response (20 μs) UV detectors, which are visible-blind and self-powered, in devices where an n-type ZnO nanowire partially lies on a p-type GaN film, are demonstrated. Moreover, a CdSe-nanowire red-light detector powered by a nanoscale ZnO/GaN photovoltaic cell is also demonstrated, which extends the device function to a selective multiwavelength photodetector and shows the function of an optical logical AND gate.