Briefly, a chain iminium cation 1a' was formed by ring opening of the ring imidazoline derivative 1a under sulfuric acidic catalysis. In microdroplets, the chain iminium 1a' was nucleophilically attacked by water on the iminium double bond to form a water coalescent intermediate 1a", and the latter may undergo proton transfer from oxygen to nitrogen and C-N bond cleavage to generate the final product 2a with elimination of protonated formaldehyde (finally deprotonated to formaldehyde). In bulk phase, the chain iminium 1a' may undergo resonance of the iminium double bond to form a carbocationium intermediate 1a", which may further electrophilically be attack by the adjacent arene carbon and form a benzofused 7-membered N-heterocycle product 3a after dehydrogenation. In addition, vicinal diamine 2a may undergo a series of oxidation and nucleophilic attack of the iminium double bond by water in bulk phase, and finally form the imine product 4a by the elimination of the substituted (phenylamino)hydroxymethyl. It should be noted that more studies should be undertaken to uncover the inherent mechanism on how organic microdroplets drive the different reaction pathways.