Ethyl α‐(Triphenylphosphoranylidene)amino‐β‐ferrocenylacrylate as a Starting Material for [2+2] Cycloadditions, Including the Aza‐Wittig Reaction

Ethyl α‐(triphenylphosphoranylidene)amino‐β‐ferrocenylacrylate, synthesized from the corresponding azide, was treated with a few selected electrophilic agents potentially capable of undergoing the aza‐Wittig reaction. The transformations with aroyl chlorides and phenylisocyanate afforded a series of novel 4‐(ferrocenyl)methylidene‐2‐aryloxazolones. On treatment of the phosphorimino compound with DMAD two competitive reactions took place on the C=C and N=P bonds, giving rise to a novel amino(ferrocenyl)butadiene and a ferrocenyl‐substituted aza‐pentadienylphosphorylide, respectively. The parent azidoferrocenylacrylate underwent the expected 1,3‐dipolar cycloaddition with DMAD, resulting in a triester of a (ferrocenyl)vinyl‐substituted v ‐triazoletricarboxylate suitable for a variety of further heterocyclic syntheses. The structures of the new compounds were determined by IR and NMR spectroscopy, mass spectrometry, and X‐ray analysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)