Synthesis of Natural Product-like Polyheterocycles via One-Pot Cascade Oximation, C–H Activation, and Alkyne Annulation

An efficient protocol
for the direct transformation of chroman-4-ones
to tricyclic fused pyridines with the skeleton of cassiarins, a family
of alkaloids with antimalarial activity, was developed. Also, a general
strategy for modular construction of polyheterocycles with diverse
natural product-like skeletons was developed by using ketone–alkyne
bifunctional substrates. These reactions involved a one-pot cascade
oximation of ketones, rhodium-catalyzed C–H activation, and
intermolecular/intramolecular alkyne annulations under mild conditions
with high atom, step, and redox economy.