A series of 1,2-dihydroquinolines were synthesized in good to excellent yields by reacting 2-aminobenzaldehyde derivatives and dialkyl acetylenedicarboxylates with catalytic amounts of phosphine. This reaction was rendered catalytic by the selective in situ phosphine oxide reduction with the use of phenylsilane. Furthermore, with the same starting materials and with an additional role of the reducing agent, a new olefination reaction was discovered. Hydrogen/deuterium (H/D) exchange experiments revealed the possible mechanism of this reaction.