Assembly of Thiazino[3,4-a]isoquinoline and Thiazepino[5,4-a]isoquinoline Frameworks from Isoquinolinium 1,4-Zwitterionic Thiolates via [5 + 1] and [5 + 2] Cycloaddition Reactions

Two cycloaddition modes of isoquinolinium 1,4-zwitterionic thiolates have been established. Upon choosing α-bromo ketones as the counterpart, a range of isoquinoline-fused thiazines can be attained with yields ranging from moderate to excellent through a formal [5 + 1] reaction pathway, exhibiting remarkable substrate adaptability and resilience to diverse functional groups. Additionally, a library of unprecedented thiazepino[5,4-a]isoquinolines, a novel category of seven-membered heterocycles, has been synthesized via a [5 + 2] pathway utilizing acetylenedicarboxylate as the reactive component. Notably, this reaction process stands out for its exceptional 100% atomic utilization efficiency.