Recent Advances in Mechanochemical Organic Synthesis

In this review, the recent advances in mechanochemical organic synthesis are presented. These include variety of chemical reactions, organic functional group transformations, organic catalytic processes, and photochemical reactions which were not carried in mechanochemical conditions before

Mechanochemical synthesis of thioureas, ureas and guanidines

In this review, the recent progress in the synthesis of ureas, thioureas and guanidines by solid-state mechanochemical ball milling is highlighted. While the literature is abundant on their preparation in conventional solution environment, it was not until the advent of solvent-free manual grinding using a mortar and pestle and automated ball milling that new synthetic opportunities have opened. The mechanochemical approach not only has enabled the quantitative synthesis of (thio)ureas and guanidines without using bulk solvents and the generation of byproducts, but it has also been established as a means to develop "click-type" chemistry for these classes of compounds and the concept of small molecule desymmetrization. Moreover, mechanochemistry has been demonstrated as an effective tool in reaction discovery, with emphasis on the reactivity differences in solution and in the solid state. These three classes of organic compounds share some structural features which are reflected in their physical and chemical properties, important for application as organocatalysts and sensors. On the other hand, the specific and unique nature of each of these functionalities render (thio)ureas and guanidines as the key constituents of pharmaceuticals and other biologically active compounds

The Utility of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as a Hydrogen Bond Acceptor in the Design of Novel Superbasic Guanidines – A Computational Study

New guanidine-derived superbases with TBD-functionalized alkyl side chains have been developed using a computational DFT approach. Exploiting the high hydrogen bond basicity of TBD allowed ac-cess to systems with strong charge-assisted intramolecular hydrogen bonds in the protonated state. The enhanced stability of such guanidines is mirrored in their gas-phase basicities, which cover the range from 1044−1168 kJ mol−1, depending on the number of alkyl side chains, the type of alkyl spac-er and the hydrogen-bonding pattern

Synthesis of monosubstituted thioureas by vapour digestion and mechanochemical amination of thiocarbamoyl benzotriazoles

Thiocarbamoyl benzotriazoles, as safe and easy-to-handle isothiocyanate equivalents, were quantitatively converted to N-monosubstituted thioureas by vapour digestion synthesis under an ammonia atmosphere. This simple, but timely process provided a synthetic platform that enabled the “slow” amination reaction to be successfully transformed into a rapid one aided by mechanochemical milling. The ammonium chloride/sodium carbonate equimolar mixture allowed in situ formation of ammonia under ball-milling conditions. This novel and green approach yielded aromatic and aliphatic primary thioureas in near-quantitative isolated yields with workup entirely based on using only water. In addition, the molecular and crystal structures of selected polyaromatic primary thioureas were determined from the synchrotron powder diffraction data

Mechanochemical Catalytic Transfer Hydrogenation of Aromatic Nitro Derivatives

Mechanochemical ball milling catalytic transfer hydrogenation (CTH) of aromatic nitro compounds using readily available and cheap ammonium formate as the hydrogen source is demonstrated as a simple, facile and clean approach for the synthesis of substituted anilines and selected pharmaceutically relevant compounds. The scope of mechanochemical CTH is broad, as the reduction conditions tolerate various functionalities, for example nitro, amino, hydroxy, carbonyl, amide, urea, amino acid and heterocyclic. The presented methodology was also successfully integrated with other types of chemical reactions previously carried out mechanochemically, such as amide bond formation by coupling amines with acyl chlorides or anhydrides and click-type coupling reactions between amines and iso(thio)cyanates. In this way, we showed that active pharmaceutical ingredients Procainamide and Paracetamol could be synthesized from the respective nitro-precursors on milligram and gram scale in excellent isolated yields