| Summary: | (<i>E</i>)-1-(1<i>H</i>-Benzo[<i>d</i>]imidazol-2-yl)-3-(dimethylamino)prop-2-en-1-one <b>2</b> was synthesized by one-pot synthesis protocol of 2-acetyl benzo[<i>d</i>]imidazole with dimethylformamide dimethylacetal (DMF-DMA) in xylene at 140 °C for 8 h. Reaction of enaminone derivative <b>1</b> with acetylacetone in the presence of AcOH/NH<sub>4</sub>OAc under reflux afforded the cyclized pyridino-benzo[<i>d</i>]imidazole derivative <b>3</b>. The latter compound was converted into the corresponding <i>β</i>-enaminone <b>4</b> with DMF-DMA. The single crystal X-ray diffraction technique eventually confirmed the assigned chemical structure of the <i>N</i>-alkyl-<i>β</i>-enaminone <b>2</b> and pyridino-benzo[<i>d</i>]imidazole derivative <b>3</b>. <i>N</i>-alkyl-<i>β</i>-enaminone <b>2</b> crystallized in the monoclinic space group P2<sub>1</sub>/n with unit cell parameters of <b>a</b> = 9.8953(3) Å, <b>b</b> = 5.7545(2) Å, <b>c</b> = 21.7891(7) Å, and β =100.627(2)°, and with one molecule per asymmetric unit. On the other hand, compound <b>3</b> crystallized in the orthorhombic crystal system and space group P2<b><sub>1</sub></b>2<b><sub>1</sub></b>2<b><sub>1</sub></b> with unit cell parameters of <b>a</b> = 6.82950(10) Å, <b>b</b> = 8.00540(10) Å, <b>c</b> = 22.4779(2) Å, and also with one molecule per asymmetric unit. Based on Hirshfeld analysis, the H...H (51.3%), O...H (10.0%), N...H (10.3%), and C...H (27.6%) contacts in <b>2</b> and the H...H (46.8%), O...H (9.9%), N...H (13.0%), and C...H (21.6%) in addition to the C…C (6.7%) interactions in <b>3</b> are the most important towards crystal stability via molecular packing. The main difference is the presence of π–π interaction among the molecular units of <b>3</b> but not in <b>2</b>. The calculated <sup>1</sup>H and <sup>13</sup>C NMR chemical shifts showed good agreements with experimental data. Electronic properties and reactivity parameters of both compounds are also calculated and compared.
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