Indium triflate catalyzed one-pot multicomponent synthesis of spiro-hexahydropyrimidines explained by multiple covalent bond formation

A mild, efficient, and expeditious method has been developed for the synthesis of spiro-hexahydropyrimidine derivatives via a three-component, one-pot cyclocondensation reaction of aromatic amines, formaldehyde, and cyclic ketones in 4-6 h using In(OTf) ₃ as Lewis acid catalyst for the first time. The reaction involving creation of six new covalent bonds was efficiently promoted by 10 mol % In(OTf) ₃ and the catalyst could be recovered easily after the reaction and reused without any loss of its catalytic activity. The advantageous features of this methodology are high atom-economy, operational simplicity, shorter reaction time, and easy handling.