A highly chemo- and regioselective synthesis of heterocyclic [3.3.3]propellanes via sequential multicomponent reactions in water

A simple and highly chemoselective heteroannulation protocol for the synthesis of polysubstituted heterocycles is reported. In this work, various oxa-aza[3.3.3]propellanes were synthesized via a sequential one-pot reaction of ninhydrin, malononitrile and nitroketene acetal or nitroketene aminals in water at ambient temperature. This successive Knoevenagel condensation/Michael addition/cyclization sequence features high atom economy, excellent efficiency, and the use of water as a solvent without the need for metal catalysts or external activators. This method can be presented as a good example of group-assisted purification (GAP), in which traditional purification techniques such as recrystallization and column chromatography are avoided and pure products are obtained simply by washing the crude products.