Divergent and Regioselective Synthesis of (Trifluoromethyl/carboxyethyl)benzo[4,5]imidazo[1,2‐a]pyrimidines from β‐Enamino Diketones

• Published in: European journal of organic chemistry Vol. 2020; no. 41; pp. 6478 - 6484
• Main Authors: Andrade, Valquiria P., Mittersteiner, Mateus, Bonacorso, Helio G., Martins, Marcos A. P., Zanatta, Nilo
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 08.11.2020
• Subjects: 1,3‐Diketones; Acylated enaminones; Chemistry; Chemistry, Organic; Imidazopyrimidines; Physical Sciences; Science & Technology; Triflouromethyl; β‐Enaminodiketones; KETONES; Triflouromethyl; Imidazopyrimidines; PYRAZOLES; SERIES; 1,3-Diketones; HETEROCYCLES; Acylated enaminones; beta-Enaminodiketones
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.202001142

A divergent and regioselective cyclocondensation reaction of β‐enamino diketones with 2‐aminobenzimidazole is reported. The β‐enamino diketones react with 2‐aminobenzimidazole to form exclusively 1,2‐ or 1,4‐regioisomers of benzo[4,5]imidazo[1,2‐a]pyrimidines, depending on the nature of the EWG group in the diketones: when the diketone has a carboxyethyl group, only the 1,2‐regioisomer was obtained; and when the EWG = CF3, only the 1,4‐regioisomer was isolated. The structure of the obtained products was unambiguously determined by 2D‐NMR experiments and single‐crystal X‐ray analysis. β‐Enamino diketones were cyclocondensed with 2‐aminobenzimidazole to selectively furnish 1,2‐ or 1,4‐regioisomers of benzo[4,5]imidazo[1,2‐a]pyrimidines. The selectivity of the reaction was found to be mainly due to the nature of the group (trifluoromethyl or carboxyethyl) attached to the ketone moiety.