Experimental and theoretical approaches to [1,5]-prototropic generation of an azomethine ylide and a 1,3-dipolar cycloaddition for novel spiropyrrolidine oxindoles synthesis

A series of spiropyrrolidine oxindoles was synthesized via a multicomponent 1,3-dipolar cycloaddition reaction of isatin, benzylamine and chalcone derivatives. The regio- and stereochemistry of the products were established by single crystal X-ray structure and spectroscopic techniques. The molecular mechanism of this cycloaddition has been investigated by means of a density functional theory (DFT) method. The energy path in preparing the azomethine ylide via a [1,5]-H shift in an iminium ion was evaluated. The regio- and stereoselectivity were explained on the basis of transition states stabilities, global and local reactivity indices of the reactants. The cycloaddition has been assumed to take place through one-step pathway in which two C–C bonds are formed in a nonsynchronous way.