Synthesis of 2‐Phosphaindolizine and [1,3]Azaphospholo[1,5‐ a ]quinoline

The reaction of (chloromethyl)dichlorophosphine ( 1 ) with 2‐[(trimethylsilyl)methyl]pyridine ( 6 ) and 2‐[(trimethylsilyl)methyl]quinoline ( 12 ) in THF affords unsubstituted parent 2‐phosphaindolizine ( 5 ) and [1,3]azaphospholo[1,5‐ a ]quinoline ( 7 ). Multinuclear low‐temperature NMR spectroscopy was used to investigate the reaction mechanism; a cascade of substitution and cyclization steps involving transient picolylphosphines and phosphorus heterocycles was identified. The molecular and crystal structures of two heterocyclic intermediates and of 7 were determined by single‐crystal X‐ray diffraction. Moreover, all intermediates and products were characterized by multinuclear 1 H, 13 C and 31 P NMR spectroscopy.