A mechanochemical [2+2+2] cycloaddition facilitated by a cobalt(<scp>ii</scp>) catalyst and piezoelectric materials

In this study, we present the first general mechanochemical protocol for the catalytic [2+2+2] cycloaddition of alkynes <i>via</i> a simple and inexpensive cobalt(ii)-based catalytic system. The key to achieving the high efficiency of this mechanochemical transformation is the use of piezoelectric BaTiO₃ as a reductant in combination with an amine additive to facilitate the generation of a catalytically active low-valent cobalt species. This method is characterized by a broad substrate scope, short reaction times, solvent-less conditions, and the feasibility of reacting poorly soluble substrates. Thus, we provide a more efficient, broadly applicable, and sustainable alternative to existing solution-based protocols.