A new class of planar-chiral ferrocenes: Serendipitous formation of 1,2-ferrocenediylazaphosphinines

The reaction of 1-(α-aminoalkyl)-2-diphenyl-phosphinoferrocene (1) which 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 cyclo-propanation of styrene by ethyl diazoacetate revealed a complete diastereo-discrimination leading to the formation of trans-product in 100% yield.