Assembly of Thiazino[3,4‐<i>a</i>]Isoquinoline and Thiazepino[5,4‐<i>a</i>]Isoquinoline Frameworks from Isoquinolinium 1,4‐Zwitterionic Thiolates Through [5+1] and [5+2] Cycloaddition Reactions

Abstract 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.