Syntheses of Iso‐Condensed Heteroaromatic Pyrroles

Three novel reactions for the synthesis of iso‐condensed heteroaromatic pyrroles: (1) tandem intramolecular 1,3‐dipolar cycloaddition and cycloreversion reaction; (2) phosphineimine‐alkylidenemalonate cyclization reaction; (3) retromalonate addition reaction, are described. They can be used in acidic, neutral or basic conditions respectively. Iso‐condensed heteroaromatic pyrroles, such as pyrrolo[3,4‐b]indole 12, pyrrolo[3,4‐b]pyridine 17, pyrrolo[3,4‐c]pyridine 18, thieno[2,3‐c]pyrrole 37, pyrrolo[3,4‐b]pyrrole 40, pyrrolo[3,4‐b]pyrazine 49, benzofuro[2,3‐c]pyrrole 50, 1,2‐bis[5‐thieno[2,3‐c]pyrrolyl]ethane 51, 1,4‐bis[5‐thieno[2,3‐c]pyrrolyl]benzene 52, dipyrrolo[3,4‐b;3′,4′‐d]dipyrroles 55 and 56, benzotripyrroles 62–64, and thieno[3,4‐c]pyrroles 67 and 73 are synthesized efficiently according to these methods.