Mechanochemically Induced Cross Dehydrogenative Coupling Reactions under Ball Milling

Abstract

Cross dehydrogenative coupling (CDC) reactions have become a convenient synthetic strategy for the synthesis of various (het)aromatic scaffolds. In recent times ball milling has emerged as a powerful tool to perform reactions in a greener way. The current review highlights various applications of cross dehydrogenative coupling reactions under ball milling towards synthesis of useful molecules in a more efficient and convenient manner.

A fruitful century for the scalable synthesis and reactions of biphenyl derivatives: applications and biological aspects

“…42 In this context, noteworthy is the contribution of Krizewsky with Turner using a CuCl 2 promoted homocoupling reaction instead of CrCl 3 (Scheme 3). 17,42,43…”

“…In 1914, Bennett and Turner demonstrated the homodimerization of Grignard reagent and phenyl magnesium bromide which promoted by chromium(III) chloride (CrCl 3 ) or anhydrous cupric chloride (CuCl 2 ). 17 Kumada depicted the reaction of aryl halides with arylmagnesium halide or organozinc in the presence of transition metal catalysts. [18][19][20] Whereas, Hiyama produced biaryls via coupling the readily available organosilanes with organohalides.…”

“…Wurtz reported the rst trial for C(sp 3 )-C(sp 3 ) bond formation through using the sodium-mediate coupling reaction of two alkyl halides. 17 In 1862, the reaction was extended by Fittig to include coupling between aryl anion and an electrophile such as aryl halide in the presence of various metal surface such as Na, Li, Au, Cu and Ag. 30 Wurtz-Fittig reaction could be achieved via the free radical mechanism 31 in three steps; dehalogenation, followed by diffusion of the dehalogenated molecules, and nally, coupling process between two aryl halides 1 to afford biphenyl derivative 2.…”

“…42 In this context, noteworthy is the contribution of Krizewsky with Turner using a CuCl 2 promoted homocoupling reaction instead of CrCl 3 (Scheme 3). 17,42,43 Ultimately, treatment of the tetrauoro-3-methoxybenzene (4) with CuCl 2 and lithium tert-butoxide (t-BuOLi) in the presence of O 2 gas produced a mixture of biphenyl coupling product 5 (56%) and the corresponding phenol 6 (38%). The proposed mechanism involves in situ deprotonation with oxidative dimerization has been studied by Do et al 44 The production of corresponding phenol was reasonable through trapping of the formed aryl lithium with oxygen gave rise to an aryl anion species which was less prone to oxygenation and more likely to form a copper adduct that would undergo oxidative coupling reaction (Scheme 4).…”

α-C–H functionalization of glycine derivatives under mechanochemical accelerated aging en route the synthesis of 1,4-dihydropyridines and α-substituted glycine esters

“…12 Their synthesis mostly relies on the multicomponent reactions of aldehydes, β-ketoesters, and specific amine sources, which is known as Hantzsch-type synthesis. 12 a , c ,13 Recently, the development of cascade cross dehydrogenative coupling (CDC) 14 -cyclization strategy 15 has provided an efficient alternative for the synthesis of 1,4-DHPs using glycines as accessible building blocks. For example, Jia 15 a developed the first Fe/TMSCl-TBPA + /O 2 promoted cascade CDC between glycinates and β-ketoesters in acetonitrile solvent to achieve 1,4-DHPs, where the cleavage of the C–N bonding and the reassembly of amine fragments led to the bond formation in an atom- and step-economic fashion.…”