Microdroplet reaction conditions: 0.005 mol L -1 imidazoline derivatives 1 and 2.3 equiv. H2SO4 were added in 1 mL MeCN or THF; microdroplets were sprayed at 15 μL min -1 by N2 under 101.5 eq at 40 °C and were collected in a 25 mL glass beaker for 10 min. b THF was used as the solvent. c THF was used as the solvent and only 1.8 equiv. H2SO4 was used as catalyst. Bulk Reaction conditions: 0.025 mol L -1 imidazoline derivatives 1 and 18.4 equiv. H2SO4 were added in 2 mL MeCN or THF and the solution was stirred vigorously at 60 °C for 12 h. a Yield of isolated 3. b THF was used as the solvent. d THF was used as the solvent and only 3.68 equiv. H2SO4 was used as catalyst. The reaction time was increased to 24 h.