2-Fluorobenzaldehyde (1) and pipecolic acid (7) react in dimethyl sulfoxide with potassium carbonate to form benzylidene-oxaindolizidines 4. These diastereomers yield with acids uniform salts, so from 4 with hydrogen chloride results (E)-3-(2-fluorobenzylidene)-1-[1,2-bis(2-fluorophenyl)-2- hydroxyethyl]-3,4,5,6-tetrahydropyridinium chloride (6·Cl), elucidated by X-ray structural analysis. Treatment of 6·Cl with alkali hydroxide regenerates 4. Similarly proline (13), when treated with two equivalents of 1, gives rise to oxapyrrolizidines 14. From 14 in presence of 1 the perchlorate of the benzylidene derivative 15·ClO4 can be obtained which is transformed to benzylideneoxapyrrolizidines 15 by bases.