Heterogeneous SnCl₂/SiO₂ versus Homogeneous SnCl₂ acid catalysis in the benzo[N,N]-heterocyclic condensation

摘要

The scope of homogeneous Lewis acid-catalyzed benzo[N,N]-heterocyclic condensation was expanded to include the use of various metal salts not reported in the literature and SnCl2·2H2O was finally selected. Among various solid supports activated with SnCl2, heterogeneous SnCl2/SiO2 proved to be the most effective and significantly higher conversions were achieved compared to SnCl2·2H2O itself. The results of TG-DTA and BET indicated that dispersed SnCl2 coordinates with surface hydroxyl groups of silica leading to formation of stable Lewis acid sites. Low catalyst loading, operational simplicity, practicability and applicability to various substrates render this eco-friendly approach as an interesting alternative to previously applied procedures.