A new concept in organocatalysis allowing for the construction of cyclobutanes with four contiguous stereocenters with complete diastereo- and enantiomeric control by a formal [2 + 2]-cycloaddition is presented. The concept is based on simultaneous dual activation of α,β-unsaturated aldehydes and nitroolefins by amino- and hydrogen-bonding catalysis, respectively. A new bifunctional squaramide-based aminocatalyst has been designed and synthesized in order to enable such an activation strategy. The potential and scope of the reaction are demonstrated, and computational studies which account for the stereochemical outcome are presented.

Light-regulated drugs allow remotely photoswitching biological activity and enable plausible therapies based on small molecules. However, only freely diffusible photochromic ligands have been shown to work directly in endogenous receptors and methods for covalent attachment depend on genetic manipulation. Here we introduce a chemical strategy to covalently conjugate and photoswitch the activity of endogenous proteins and demonstrate its application to the kainate receptor channel GluK1. The approach is based on photoswitchable ligands containing a short-lived, highly reactive anchoring group that is targeted at the protein of interest by ligand affinity. These targeted covalent photoswitches (TCPs) constitute a new class of light-regulated drugs and act as prosthetic molecules that photocontrol the activity of GluK1-expressing neurons, and restore photoresponses in degenerated retina. The modularity of TCPs enables the application to different ligands and opens the way to new therapeutic opportunities.

A series of azobenzene-based thiourea catalysts have been developed with the aim of achieving control over the catalytic activity by the use of light. The conceptual design of these systems relies on the inactivation by means of intramolecular hydrogen bonding, only likely to take place in one of their isomeric forms. After fine structure modulation of the catalyst a substantial difference in activity has been observed between the irradiated and the nonirradiated reaction. Furthermore, the system allowed in situ manipulation of the catalyst activity during the course of a given experiment.

A polystyrene-supported 1,1'-bi-2-naphthol derived phosphoric acid has been synthesized and applied in the enantioselective Friedel-Crafts reaction of indoles and sulfonylimines. The immobilized catalyst was highly active and selective, and gave rise to a broad range of 3-indolylmethanamines (19 examples) in high yields and excellent enantioselectivities (up to 98 % enantiomeric excess) after short reaction times under very convenient reaction conditions (RT in dichloromethane). Moreover, repeated recycling (14 cycles) was possible with no substantial loss in catalytic performance and the system could be adapted to a continuous-flow operation (6 h). Finally, the applicability of the system was further confirmed by rapid access to a library of compounds with three points of diversity in a single continuous-flow experiment that involved sequential pumping of different substrate combinations.

Giving directions: optically active dihydropyrans bearing three contiguous stereogenic centers can be efficiently prepared by the title reaction. High stereo- and regiocontrol can be achieved by employing a bifunctional H-bond-directing aminocatalyst.

The fast and highly stereoselective Mannich reaction of aldehydes and ketones with the N-(p-methoxyphenyl) ethyl glyoxylate imine catalyzed by polystyrene resins functionalized with (2S,4R)-hydroxyproline is reported. The effect of the nature of the linker connecting proline with the polymeric backbone has been studied, and a 1,2,3-triazole linker constructed from azidomethyl polystyrene and O-propargyl hydroxyproline turns out to be optimal for catalytic activity and enantioselectivity. With aldehyde donors, fast reactions leading to complete conversion in 1-3 h are recorded in DMF. With ketone donors, the reactions tend to be slower, but can be efficiently accelerated (six-membered ring cycloalkanones) by low-power microwave irradiation. This approach, which greatly facilitates product isolation since the catalyst is removed by simple filtration, has allowed the implementation of the reactions of aldehyde substrates in a continuous-flow, single-pass system. In this manner, the continuous synthesis of the enantiomerically and diastereomerically pure adducts (syn/anti>97:3; ee>99 %) has been achieved at room temperature with residence times of 6.0 min. This methodology has allowed for the preparation of up to 7.8 mmol of the desired Mannich adduct through the use of 0.46 mmol of catalytic resin (5.9 mol %), in a greatly simplified experimental protocol that avoids purification steps.

The widely applicable TRIP phosphoric acid catalyst has been immobilized on polystyrene using a copolymerization-based strategy. The resin (PS-TRIP) has proven to be highly active and enantioselective in the asymmetric allylboration of aldehydes. Moreover, it has shown to be extremely robust, as it can be reused for 18 times, after which it still retained its activity. Lastly, to further prove the benefits of the immobilization, a continuous flow experiment spanning 28 h has been carried out with very high yields and ee's.

Sustainability concerns are reshaping the way chemists work, not only at the stage of process design, but also when actually performing reactions. This change of paradigm is exemplified by the deployment of continuous flow techniques, which are slowly becoming a mainstream practice. Indeed, the possibility of performing catalytic processes (the flagship of sustainable chemistry) in flow presents distinctive advantages. Thus, several authors are focusing their efforts in trying to get the best of these two worlds, with the consequent challenge of finding common solutions for their respective issues. In the last years, this approach has been taken one step further with the use in flow processing of enantioselective organocatalysts, which allow the production of enantiopure compounds free of metal contaminants. Herein, we will cover the literature concerning the use of solid-supported organocatalysts for the continuous flow production of enantiomerically enriched compounds.