Insertion of ammonia into alkenes to build aromatic N-heterocycles

Aromatic heterocycles containing nitrogen are ubiquitous in biologically relevant small molecules. Here the authors show an unorthodox methodology for their synthesis, by inserting the nitrogen atom into a carbon ring, with ammonia in electrochemical conditions. Ammonia is one of the most abundant and simple nitrogen sources with decent stability and reactivity. Direct insertion of ammonia into a carbon skeleton is an ideal approach to building valuable N-heterocycles for extensive applications with unprecedented atom and step economy. Here, we show an electrochemical dehydrogenative method in which ammonia is inserted directly into alkenes to build aromatic N-heterocycles in a single step without the use of any external oxidant. This new approach achieves 98-99.2% atom economy with hydrogen as the only byproduct. Quinoline and pyridine with diverse substitutions are readily available. In this work, electrochemistry was used to drive a 4-electron oxidation reaction that is hard to access by other protocols, providing a parallel pathway to nitrene chemistry. In a tandem transformation that included three distinct electrochemical processes, the insertion of ammonia further showcased the tremendous potential to manipulate heterocycles derived from Hantzsch ester to diazine via pyridine and pyrrole.