Ethyl α-(triphenylphosphoranylidene)amino-β-ferrocenylacrylate as a starting material for [2+2] cycloadditions, including the aza-Wittig reaction

Ethyl alpha-(triphenylphosphoranylidene)amino-beta-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. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.