Diversity in the course of the reactions of the 4‐halogenoisoquinolines with potassium amide in liquid ammonia and with piperidine

The reactions of the 4‐X‐isoquinolines (X=F, Cl, Br, I) with potassium amide in liquid ammonia were investigated. In amounts depending on the halogen present, 1‐amino‐4‐X‐isoquinoline and 1‐aminoisoquinoline are formed by a Chichibabin‐type reaction and an abnormal AE mechanism, respectively. Evidence for the intermediate tetrahedral complex in position 1 was obtained by PMR measurements on 4‐chloroisoquinoline. In the case of 4‐bromo‐ and 4‐iodoisoquinolines reduction and coupling processes occur at the same time, leading to isoquinoline, 4,4′‐biisoquinoline and 1‐amino‐4,4′‐biisoquinoline, probably via a carbanion initially formed. Abnormal substitution was also established together with the normal AE process in the reactions of 4‐chloro‐, 4‐bromo‐ and 4‐iodo‐isoquinolines with piperidine, yielding both 1‐piperidinoisoquinoline and 4‐piperidino‐isoquinoline.