Modular synthesis of rare N-heterocycles by nitrogen insertion into allylic nucleophiles

<jats:p>N-Heterocycles are crucial targets in medicinal chemistry, agrochemistry, and materials science. Hence, the modular assembly of heterocyclic scaffolds through cyclization of linear precursors has been a longstanding focus for synthetic chemists. Here, we report an interrupted oxidative amination of easily accessible allylic alcohols and amines that transiently generates azaallenium salts, whose allene-like orbital configuration enables a facile, formally Baldwin-disfavored 5-endo-trig cyclization. The reaction is operationally simple, highly functional group-tolerant, and amenable to a range of nucleophiles. This reactivity unlocks access to rare, semi-saturated N-heterocycles that are synthetically challenging to obtain by other methods. As demonstrated in this work, they can serve as versatile synthetic intermediates, undergoing downstream aromatization or reduction to access other heterocycles. Overall, this study demonstrates that nitrogen insertion into allylic nucleophiles opens new synthetic avenues for the synthesis of rare N-heterocycles.</jats:p>