An Unprecedented Organocascade Synthesis of Functionalized Bicyclic Nitrones from 2-Aminomalonate Derived Nucleophiles and 1-Nitro-1,3-Enynes via Allenes Formation and Subsequent Rearrangement

An efficient organocatalytic cascade reaction for synthesising functionalized bicyclic nitrones is reported. The reaction of dielectrophilic ethyl 2-(nitromethylene)-4-arylbut-3-ynoate and (E)-diethyl 2-((2-hydroxybenzylidene)-amino)malonates to give a unique nitrone scaffold in the presence of a catalytic amount of DABCO is described. The working mechanism was proposed to proceed with allene formation followed by intramolecular cyclization and the rearrangement of an oxygen atom in the nitro group. A broad range of substrates was accessed in this facile chemical transformation, in which the bicyclic nitrones were isolated in moderate to good yields (19% to 79%) with excellent diastereoselectivity (>20:1 dr). (Figure presented.).