Mechanochemistry in Organic Synthesis

According to the accepted definition, mechanochemical reactions are those performed by direct absorption of mechanic energy [17]. Chemical reactions promoted by mechanical force are ever more frequendy explored in organic synthesis [18-21]. It was demonstrated that mechanochemical reactions can be performed in the absence of any solvent and therefore meet the challenges of modem chemistry that require economic use of energy and auxiliary materials and fulfill the requirements for environmentally acceptable processes (Sect. 1.3.2). 

The next two examples illustrate the successful application of mechanochemical conditions in organic synthesis. 

Interestingly, when in substrates 13 Hal=Cl, they proved completely nonreactive under standard conditions in apolar organic solvents, revealing insufficient Pd-catalyzed activation of the aryl-Cl bond. This energetically demanding step is surmounted in the mechanochemical variant, optimizing some parameters such as rotation speed and ball diameter [23]. 

The authors revealed that aromatic aldehydes 15 react with malononitrile, affording geminal dicyano derivatives 17 in high yield. Interestingly, using 15-mm-diameter steel balls, the yields increased substantially when the rotation was doubled from 400 to 800 rpm. 

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