The bifunctional acid–base catalyst piperidinomethane piperidium tetrafluoroborate (A) catalyzes the Michael addition.

Piperidinomethane piperidium tetrafluoroborate (A) catalyzes a condensation reaction and subsequent Michael addition in one-pot.

A plausible cooperative effect between the acid and basic sites of the catalyst stabilizes the transition state.

This bifunctional catalyst A has been extensively applied to the one-pot synthesis of thioethers, 2H-chromenes and 2H-quinolines.