Transition metal-free [3+3] annulation of cyclopropanols with β-enamine esters to assemble nicotinate derivatives

A metal-free and efficient approach for the synthesis of structurally important nicotinates through 4-HO-TEMPO-mediated [3 + 3] annulation of cyclopropanols with beta-enamine esters is presented. This protocol features high atom efficiency, green waste, simple operation and broad substrate scope. Moreover, the experiments of gram-scale synthesis and recovery of oxidants make this strategy more sustainable and practical. An atom-economical synthetic approach for preparing structurally important nicotinates under metal- and additive-free conditions was developed.