Novel 7-(1H-pyrrol-1-yl)spiro[chromeno[4,3-b]quinoline-6,1′-cycloalkanes]: synthesis, cross-coupling reactions, and photophysical properties

This paper covers the synthesis of a series of eleven examples of new 7-(1H-pyrrol-1-yl)spiro[chromeno[4,3-b]quinoline-6,1′-cycloalkanes] (3), where cycloalkanes are cyclopentane, cyclohexane, and cycloheptane. Heterocyclic system 3 was successfully obtained in 53–78% yields by the Clauson–Kaas reaction, in which 7-amino-spiro[chromeno[4,3-b]quinoline-6,1′-cycloalkanes] (1) were reacted with 2,5-dimethoxytetrahydrofuran (2) in an acetic acid medium at 90 °C for 48 h. Then, to demonstrate synthetic applicability, the 9-bromoquinoline-substituted derivative 3h was selected and successfully employed in traditional CC and CN cross-coupling reactions, yielding three new modified tacrine scaffolds (4–6). Photophysical studies of π → π* and n → π* transitions corroborated the aromatic structures of the heterocycle molecules and showed high emission properties, good Φf values, and moderate to large Stokes shifts (SS).