Cu/Mn co-oxidized cyclization for the synthesis of highly substituted pyrrole derivatives from amino acid esters: a strategy for the biomimetic syntheses of lycogarubin C and chromopyrrolic acid.

An effective and concise approach to synthesis of tetrasubstituted pyrroles from readily available amino acid esters by the promotion of Cu(OAc)2 in conjunction with Mn(OAc)3 has been developed. This reaction proceeds through multiple dehydrogenations, deamination, and oxidative cyclization. This oxidized system tolerates substrates bearing various electron-donating or electron-withdrawing groups. With this methodology, several key intermediates of natural products have been effectively prepared, and the total syntheses of lycogarubin C and chromopyrrolic acid have been completed in high efficiency.