Thiazolo[4,5-c]isoquinoline (I), a new heterocyclic ring system, has been synthesized from 3-aminoisoquinoline (II) in four steps by reaction with potassium thiocyanate and bromine to give 3-amino-4-thiocyanoisoquinoline (VII), cyclization with hydrochloric acid to yield 2-aminothiazolo[4,5-c]isoquinoline (VIII), Sandmeyer reaction to give 2-chlorothiazolo-[4,5-c]isoquinoline (IX), and finally reduction with hydrogen iodide and red phosphorus to yield I. The attempted preparation of I via 3-amino-4-bromoisoquinoline was unsuccessful. Various 2-substituted derivatives of I were prepared by nucleophilic displacement of the chlorine atom in 2-chIorothiazolo[4,5-c]isoquinoline. The nuclear magnetic resonance and ultraviolet spectra of I and some of its derivatives were studied.
