1. R.I. Wagner, US Patents 3086053 and 3086056 (1963).
2. For reactive intermediates and acyclic valence isomers methylene(oxo)phosphoranes see: H. Heydt, in: M. Regitz, O.J. Scherer (Eds.), Multiple Bonds and Low Coordination Chemistry in Phosphorus Chemistry, Georg Thieme Verlag, Stuttgart, 1990, pp. 375.
3. Multiple Bonds and Low Coordination Chemistry in Phosphorus Chemistry;Schoeller,1990