| Summary: | Hydrolysis/[3 + 2] cycloaddition/elimination cascades employed for the synthesis of unexpected tricyclic compound derived from isoquinoline. Reaction of ethylene derivative <b>1</b> with the isoquinoline ester iminium ion <b>2</b> in alkaline medium (MeOH/NEt<sub>3</sub>) under reflux for 1 h resulted in the formation of the fused pyrrolo[2,1-<i>a</i>]isoquinoline derivative <b>3</b>. Its structure was elucidated by X-ray single crystal and other spectrophotometric tools. Hirshfeld calculations for <b>3</b> and its crystal structure analysis revealed the importance of the short O…H (19.1%) contacts and the relatively long H…C (17.1%), Cl…H (10.6%) and C…C (6.1%) interactions in the molecular packing. DFT calculations were used to compute the electronic and spectroscopic properties of the studied system. The studied compound has polar nature (3.5953 Debye). TD-DFT calculations assigned the shortest wavelength band (220 nm) to the HOMO−1→LUMO+2 (57%), HOMO−1→LUMO+4 (14%) mixed excitations. The calculated NMR chemical shifts correlated very well with the experimental data (R<sup>2</sup> = 0.93–0.94).
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