occurred. This explanation does fit the observed isotope effects. Our initial results, therefore, suggest that the great speed of many displacement reactions involving large atom nucleophiles in protic solvents may not be due so much to their polarizability as to their ease of desolvation, and that the leaving group isotope effects provide a probe for distinguishing between the two. These results are also consistent with the operation of a concerted transition state as opposed to an intermediate ion-pair mechanism such as proposed by Sneen and Larsen1 ^2 for other reactants and solvents.If these initial conclusions are substantiated by further experiments and are not found to be unduly complicated by the intervention of specific solvation of substituents,13 specific solvation of the leaving group, or mass effects upon changing the• nucleophile, the kinetic isotope effects of leaving groups may result in one of our more powerful yet subtle probes for transition-state geometry. We propose to explore these possible complications further.

Catalysis is a topic of continuous interest since it was discovered in chemistry centuries ago. Aiming at the advance of reactions for efficient processes, a number of approaches have been developed over the last 180 years, and more recently, porphyrins occupy an important role in this field. Porphyrins and metalloporphyrins are fascinating compounds which are involved in a number of synthetic transformations of great interest for industry and academy. The aim of this review is to cover the most recent progress in reactions catalysed by porphyrins in scalable procedures, thus presenting the state of the art in reactions of epoxidation, sulfoxidation, oxidation of alcohols to carbonyl compounds and C-H functionalization. In addition, the use of porphyrins as photocatalysts in continuous flow processes is covered.

Tetrabenzoporphyrins have attracted considerable worldwide attention over the last few decades. Since the discovery of these pigments, chemists, biologists, medical professionals and material scientists have devoted pronounced efforts in order to develop synthetic methods and discover useful applications for these compounds. Nowadays, tetrabenzoporphyrins occupy a prominent position in porphyrin chemistry, and this review is intended to cover the main synthetic methods and applications of these compounds.

Abstract:Benzoquinones are usually present in arthropod defence exudates. Here, we describe the chemical profiles of 12 harvestman species belonging to the neotropical family Gonyleptidae. Nine of the studied species produced benzoquinones, while three produced alkyl phenols. Two benzoquinones and one phenol exhibited biological activity against bacteria and fungi. We also studied the biosynthesis of 2-ethyl-1,4-benzoquinone by feeding Magnispina neptunus individuals with 13 C-labelled precursors; the benzoquinones were biosynthesised through a polyketide pathway using acetate and propionate building blocks.

We have investigated both batch and continuous flow photoarylations of enol-acetates to yield different α-arylated aldehyde and ketone building blocks by using diazonium salts as the aryl-radical source. Different porphyrins were used as SET photocatalysts, and photophysical as well as electrochemical studies were performed to rationalize the photoredox properties and suggest mechanistic insights. Notably, the most electron-deficient porphyrin (meso-tetra­(pentafluorophenyl)­porphyrin) shows the best photoactivity as an electron donor in the triplet excited state, which was rationalized by the redox potentials of excited states and the turnover of the porphyrins in the photocatalytic cycle. A two-step continuous protocol and multigram-scale reactions are also presented revealing a robust, cost-competitive, and easy methodology, highlighting the significant potential of porphyrins as SET photocatalysts.