Highly Diastereoselective Synthesis of <i>N</i> , <i>S</i> ‐Polyheterocyclic Scaffolds via [3 + 2] Cycloaddition of <i>N</i> ‐Phenacylbenzothiazolium Bromides

A highly efficient, metal‐free, atom‐economical green protocol for the synthesis of N , S ‐polyheterocycles via dearomative [3 + 2] cycloaddition of N ‐phenacylbenzothiazolium salts with alkylidene acenaphthylenones and barbiturate‐derived alkenes. This reaction tolerates diverse substituents on the acenaphthylenone and barbiturate partners, underscoring its broad scope and providing an efficient method to construct desired cycloadducts in good to excellent yields with high diastereoselectivity. This strategy provides the formation of two CC bonds with multiple contiguous stereocenters, including one spiro‐center, in a one‐pot reaction. Significantly, no hydro‐quenching, solvent separations, or chromatographic/recrystallization purifications are required. Overall, this efficient, selective, and eco‐friendly strategy offers rapid access to N , S ‐frameworks relevant to medicinal chemistry and materials science.