Cobalt-assisted α-activation of ketones. Their arylation and keto-enol equilibrium confined into a macrocycle

In this study, we explore the cobalt-mediated α-activation of ketones within modified porphyrin macrocycles, focusing on the arylation processes and the influence of macrocyclic confinement on keto-enol tautomerism. The activation of ketones such as acetone, butanone, 3-pentanone, and acetophenone and their possible transfer from a cobalt centre on the carbaporphyrin fragment results in the forming of new C(sp²)–C(sp³) bonds in confined macrocyclic environments of N-confused porphyrin and azuliporphyrin. Such modified ligands allow for following altered keto-enol equilibrium. They reversibly form unique structural motifs, azuleno[1,2-c]pyran and 2,4-dihydropyrano[3,4-c]pyrrole modulated by acid-base conditions and macrocyclic aromaticity. The coordination of a modified macrocycle to a rhodium(I) centre leads to a series of complexes with a final form with rhodium(III) in the cavity. The rhodium(III) centre cleaved the C(21)–C bond and transferred the acetone fragment back to the metal ion from the azulene fragment.