Iodine Promoted Efficient Synthesis of 2-Arylimidazo[1,2-a]pyridines in Aqueous Media: A Comparative Study between Micellar Catalysis and an "On-Water" Platform

Reagentless Chemistry "On-Water": An Atom-Efficient and "Green" Route to Cyclic and Acyclic β-Amino Sulfones via aza-Michael Addition Using Microwave Irradiation

A reagentless, catalyst-free, and sustainable methodology was developed for facile access to cyclic and acyclic β-amino sulfones "on-water" using a microwave. A variety of aromatic and aliphatic amines undergo double aza-Michael addition on the surface of the water with water-insoluble divinyl sulfones upon microwave irradiation at 150 °C for 10 min to mostly afford solid cyclic β-amino sulfones as easily separable products in excellent yields by simple filtration avoiding any workup steps. Thus, all atoms of the substrates are reflected in the product making it a 100% atom-efficient method. Both electron-rich and electron-deficient amines participated well in the reaction as well as good functional group tolerance was observed. The competitive experiments expectedly revealed faster reaction kinetics for electron-rich amines. The methodology was extended to acyclic β-amino sulfones by interacting phenyl/ethyl vinyl sulfones with various amines in a similar manner. Expectedly, the method afforded very low environmental factors (in a range of 0.05-0.5) and a high Ecoscale score (up to 94). In an attempt toward sustainable development, this reagent-free, metal-free, organic solvent-free, cost-effective protocol is certainly a viable alternative to the available methods for β-amino sulfones.

Pushing Photochemistry into Water: Acceleration of the Di-π-Methane Rearrangement and the Paternó-Büchi Reaction "On-Water"

Two representative organic photoreactions, namely a bimolecular photocycloaddition and a monomolecular photorearrangement, are presented that are accelerated when the reaction is performed "on-water", that is, at the water-substrate interface with no solvation of the reaction components. According to the established models of ground-state reactions "on-water", the enhanced efficiency of the photoreactions is explained by hydrophobic effects (Paternó-Büchi reaction) or specific hydrogen bonding (di-π-methane rearrangement) at the water-substrate interface that decrease the energy of the respective transition state. These results point to the potential of this approach to conduct photoreactions more efficiently in an ecologically favorable medium.

Recent Progress in Metal-Free Direct Synthesis of Imidazo[1,2-a]pyridines

This Mini-Review highlights the most effective protocols for metal-free direct synthesis of imidazo[1,2-a]pyridines, crucial target products and key intermediates, developed in the past decade. The emphases is given on the ecological impact of the methods and on the mechanistic aspects as well. The procedures efficiently applied in the preparation of important drugs and promising drug candidates are also underlined.

2-Aminopyridine - an unsung hero in drug discovery

2-Aminopyridine is a simple, low molecular weight and perfectly functionalised moiety known for the synthesis of diverse biological molecules. Many pharmaceutical companies across the globe aim to synthesise low-molecular weight molecules for use as pharmacophores against various biological targets. 2-Aminopyridine can serve as a perfect locomotive in the synthesis and pulling of such molecules towards respective pharmacological goals. The major advantage of this moiety is its simple design, which can be used to produce single products with minimum side reactions. Moreover, the exact weight of synthesised compounds is low, which enables facile identification of toxicity-causing metabolites in drug discovery programmes. This manuscript is a quick review of such pharmacophores derived from 2-aminopyridine.

Visible-light-promoted direct C3-trifluoromethylation and perfluoroalkylation of imidazopyridines

An efficient method for direct trifluoromethylation and perfluoroalkylation at C3 of imidazopyridines through visible light-promoted C-H bond functionalization was developed. Under the irradiation of a blue LED, a series of C3-perfluoroalkyl-substituted imidazopyridines were synthesized from the corresponding imidazopyridines and perfluoroalkyl iodides in moderate to good yields at room temperature. It should be mentioned that this reaction proceeded in the absence of any transition-metal catalyst, oxidant and photocatalyst.