A New Class of Planar-Chiral Ferrocenes: Serendipitous Formation of 1,2-Ferrocenediylazaphosphinines

The reaction of 1-(α-aminoalkyl)-2-diphenylphosphinoferrocene ( 1 ) with glyoxals gave via an unusual heterocyclization 1,2-ferrocenediylazaphosphinines ( 3 ) as a new class of planar-chiral ferrocenes. The products were fully characterized by analytical and various spectroscopic techniques. In particular, a complete assignment of all protons and carbons was made by various NMR techniques. A substantial degree of π-electron delocalization extending over the fused heterocyclic ring can be evidenced by IR and UV/vis spectra and in the case of 3a by X-ray crystallographic data. Employment of rac- 3a as ligand for Cu-catalyzed cyclopropanation of styrene by ethyl diazoacetate revealed a complete diastereo-discrimination leading to the formation of trans -product in 100% yield.