Reactions of Cyclopropenones with 2-Picolines: The Multistep Aerobic Cascade toward [2.3.3]Cyclazinylium-1-olates

Aerobic nonlinear cascade reaction between 2-substituted cyclopropenones and 2-picolines was discovered to afford rare pyrrolo[2,1,5-de]quinolizin-9-ium-1-olates ([2.3.3]cyclazinylium-1-olates). The reaction mechanism was studied by labeling experiments, LC-MS/NMR monitoring, and intermediates trapping. The reaction features and limitations were highlighted, and focusing on the side processes allowed the demonstration of examples of gaining high molecular complexity from simple reactants. Optical properties of the [2.3.3]cyclazinylium-1-olates and their aza-analogs were explored, and some structure–property relationships and mesomerism particularities were revealed.