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Cycloaddition reaction between azomethine ylides and p-deficient alkenes leads to densely substituted L-and D-unnatural prolines. These (3 + 2) cycloadducts in turn catalyse the preparation of an offspring of unnatural endo-and exo-L-proline derivatives. These latter compounds are also efficient catalysts of aldol reactions and yield aldol adducts with the opposite stereochemistry obtained under natural L-Pro organocatalysis.

Anthraquinones (AQs) constitute the largest group of natural pigments, are commonly found in dyes, and are widely used in the textile industry due their photostability. They combine high absorptivity in the visible region with high excited‐state reduction potentials, making them effective acceptors of electrons and hydrogen atoms. AQs can be employed as organic catalysts in photooxidation reactions as well to produce reactive oxygen species (ROS). All these methods feature green chemistry aspects such as avoiding heavy metals, reducing waste, using inexpensive reagents, employing environmentally low‐impact solvents, and oxidizing with O2. This review covers the application of AQs in photoredox catalysis.

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The stability of some Schiff-bases formed between PLP and different amino acids has been investigated in a wide range of pH. The kinetic constants of formation of these compounds and their hydrolysis rate constants have been determined. Results show that the a-position of the carboxyl group of amino acid plays an important role on the mechanism of water attack upon the C=N-bond. The absence of ionic groups in the surroundings of that bond must be an important factor of stability. Bulky hydrophobic substituents in the amino acid, near the amine part, protect the imine bond against hydrolysis.