Sequential azomethine imine cycloaddition–palladium catalysed cyclisation processes

In situ generation of azomethine imines from aryl/heteroaryl aldehydes and N,N′-disubstituted hydrazines followed by cycloaddition to N-methylmaleimide generates pyrazolidines, which undergo Pd(0) catalysed cyclisation involving the aldehyde and hydrazine substituents, with formation of 6–8 membered rings in good yield. AMI calculations indicate the preferred configuration of the azomethine imines involved and identify the most likely cycloaddition transition states.