Pyrrole-hybridized spiro[chromeno[4,3-b]cycloalka[4,5]thieno[3,2-e]pyridine]cycloalkanes as modified tacrine system: Synthesis, structure, and photophysical evaluation

Abstract

This paper reports the synthesis, structural elucidation, and investigation of the photophysical properties of a novel heterocyclic system, such as pyrrole-hybridized polyhydro-spiro[chromeno[4,3-b]cycloalka[4,5]thieno[3,2-e]pyridine]cycloalkanes (3), where the spiro-cycloalkanes are cyclopentane, cyclohexane, and cycloheptane; and the cycloalka[4,5]thieno are cyclopenta-, cyclohexa-, and cyclohepta-. These hybrid scaffolds 3 resulted from N-derivatization reactions of a series of twelve examples of modified 7-amino-substituted precursors 1, which, via the Clauson-Kaas reaction using 2,5-dimethoxy-tetrahydrofuran (2,5-DMOTHF) as a CCCC block, were applied to enable the construction and isolation of twelve mentioned pyrrole derivatives 3 in yields of 66 – 95%. Compounds 3 were structurally fully characterized by melting point, 1H-, 13C-NMR, and 1H-13C 2D-NMR (HSQC and HMBC) spectroscopy, X-ray diffraction, and HRMS analysis. The novel pyrroles 3 had their photophysical properties investigated (absorption and emission) in solution in several solvents. As a result, it was found that these pyrroles, where the transition bands were observed in the UV region, exhibit moderate luminescent and shorter lifetime decay values, which are related to and dependent on the spiro moiety and/or cycloalkanes directly fused to the thiophene ring of this new tacrine-modified system.