Facile and efficient synthesis of benzoxazoles and benzimidazoles using a Lewis acid MOF catalyst

Benzoxazoles and benzimidazoles are a valuable class of heterocyclic compounds and have numerous therapeutic applications. Herein, we present an efficient and facile synthesis of these compounds using a 3D metal-organic framework (MOF), {Mn₂(TPA)₂(DMF)₂}_n, referred to as the Mn-TPA MOF (TPAH₂ represents terephthalic acid and DMF denotes N,N-dimethylformamide) as a catalyst. The desolvated MOF, Mn-TPADesolv, with its robust nature and manganese open metal sites (OMSs) serves as an effective heterogeneous catalyst. Mn-TPADesolv efficiently facilitates the synthesis of benzoxazole and benzimidazole derivatives via the reaction of o-aminophenol or o-phenylenediamine with various aromatic aldehydes. We recorded high conversions up to 99.9% in both the reactions under optimised conditions within a short reaction time. The catalytic reactions exhibited a remarkably high turnover number (TON) up to 9990, and a turnover frequency (TOF) up to 333 min^-1 for various substrates. Notably, Mn-TPADesolv showed excellent catalytic activity for sterically hindered substrates, such as 1-naphthaldehyde and 9-anthracenecarboxaldehyde, maintaining high TON and TOF values. Furthermore, the recyclability of Mn-TPADesolv revealed that the catalyst could be reused up to 30 cycles with no loss in its structural integrity and catalytic performance. The results obtained in this study demonstrate the excellent catalytic performance of Mn-TPADesolv and emphasize its potential as a scalable, robust, cost-effective catalyst with its broad substrate scope compatibility.