Developing click reactions of a 3-ferrocenyl-2H-azaphosphirene complex.

Atom efficient reactions of 3-ferrocenyl-2H-azaphosphirene complex 1 using a newly developed acid/base ring expansion protocol are presented. Consecutive reaction of 1 in the presence of dimethyl cyanamide with triflic acid and triethylamine yielded the selective formation of 2H-1,4,2-diazaphosphole complex 3. The same protocol using acetone, benzaldehyde and ferrocenyl aldehyde afforded 1,3,5-oxazaphosphol-3-ene complexes 4, 5a,b and 6a,b, the latter as mixtures of diastereomers, which could be separated. Apart from NMR, IR and UV/vis spectroscopic data, the single-crystal X-ray structures of complexes 3, 4 and 6a are discussed.