Tandem Synthesis Ia Cadogen-Type Reaction Of 2-Nitrochalcones And Activate Methylene Isocyanides

Nitrogen compounds are widely used in medicine,pesticide,chemical and other related fields because of their significant biological and pharmacological activities.Reductive cyclization of o-functionalized nitroarenesisone is one of the most efficient tools for the synthesis of N-containing heterocycles.Among them,Cadogan reaction has attacted much attention,because this reaction could construct indoles,carbazoles and other aromatic heterocyclic compounds through the reductive cyclization of the cheap and readily available nitroarenes.As the traditional Cadogan reaction needs to be carried out at higher temperatures,recent studies have mainly focused on the development of mild reaction conditions.However,tandem Cadogan-type bicyclization of nitroarenes for the construction of complex heterocycles remains scarce.A tandem [3 + 2] cycloaddition/reductive cyclization of nitrochalcones with active methylene isocyanides for the efficient and concise synthesis of pyrrolo [2,3-b]-quinolones is reported in this thesis.The two intermediates of the tandem reaction were confirmed by the control experiment,and thus the possible reaction mechanism was proposed.In this transformation,o-nitrochalcone undergoes a formal [3 + 2] cycloaddition with activated methylene isonitrile to form intermediate dihydropyrrole,then the in situ generated dihydropyrroline acts as the internal reductant to convert the nitro into an electrophilic nitroso group,which undergoes the subsequent C-N bond formation reaction.A six-membered pyridine ring is built by forming the C-N bond in this reaction,whereas in the traditional Cadogen reaction,a five-membered pyrrole ring is generally built.Transition-metal-free,simple experimental procedure and ready accessibility of starting materials characterize the present transformation.