Fe-Catalyzed Pictet-Spengler-Type Cyclization via Selective Four-Electron Reductive Functionalization of CO2

Main observation and conclusion Herein, we describe a novel catalytic Pictet-Spengler-type cyclization using CO2 as a nontoxic and sustainable C1 feedstock with environmentally benign and non-precious-metal iron as catalyst. The reaction is achieved by selective four-electron reduction of CO2 into methylene level intermediate through carefully tuning the reaction parameters. A variety of tetrahydro-beta-carbolines and other nitrogen-containing heterocycles can be easily obtained under mild conditions. Mechanistic studies have shown that tetrahydro-beta-carbolines are probably obtained via spiroindolenine intermediates.

Automated summary

This study introduces a novel cyclization reaction using CO2 as a sustainable C1 feedstock and iron as catalyst, achieving selective reduction into methylene intermediate under carefully tuned reaction parameters. Various nitrogen-containing heterocycles can be easily obtained under mild conditions, possibly via spiroindolenine intermediates.