Dibenzoylmethane Reaction with Dichlorophenylphosphine: Oxygen Transfer from Carbon to Phosphorus via a Defined C2P 0 3 Phosphorane Wilhelm V. Dahlhoff*, Kalulu M. Taba [1], and Richard Mynott* Max-Planck-Institut für Kohlenforschung. Kaiser-Wilhelm-Platz 1, D-4330 Mülheim a.d. Ruhr. FRG Z. Naturforsch. 44b, 41—46 (1989); received August 10, 1988 Tricyclic Phosphorane, Rearrangement to Phosphinic Acid Ester, 2D NMR Spectra, 13C NMR Spectra Dichlorophenylphosphine reacts with two equivalents of dibenzoylmethane at —30 °C in the presence of triethylamine to give a tricyclic phosphorane intermediate 4 which isomerizes to the more stable phosphinic acid ester 5 above 30 °C. The structures of 4 and 5 were determined by l3C, 'H shift correlated 2D NMR spectroscopy using Introduction In the course of our work on acetylacetonate che lates [2—5] we have now also investigated the reac tion of dichlorophenylphosphine with some 1,3-di- ketones. Both dichlorophenylphosphine [6 ] and its (CO) 5 Cr— [7], (CO) 5 W - [7] and Cp(CO) 2 Mn- [8 ] derivatives are known to react with acetylacetone to give the dioxaphosphorinane ring system as the main product. This is formed by attack of both P—Cl func tions on a single molecule of acetylacetone, resulting in the removal of an a and a ß proton. Similar reac tions leading to ring formation have also been ob served in the case of dichlorophenylphosphine oxide [9], As diketones that have no ß protons obviously cannot react in this manner, it was decided to eluci date the reaction of dibenzoylmethane (1,3- diphenyl-1,3-propanedione) with dichlorophenyl phosphine. The results of this study are given below. Results A solution of dichlorophenylphosphine 2 in THF was added dropwise to a solution of dibenzoyl methane 1 and triethylamine in THF. After removal of the triethylamine hydrochloride and concentration of the solution at 0 °C a pale yellow solid product 4 was obtained. In its 'P NMR spectrum one major signal (87% of the total integral) was observed at —9.6 ppm. * Reprint requests to Dr. W. V. Dahlhoff or Dr. R. Mynott. Verlag der Zeitschrift für Naturforschung, D-7400 Tübingen 0932-0776/89/0100-0041/$ 01.00/0 long range couplings. On heating 4 above 30 °C, pure 5 was formed, which was isolated in 58% yield after recrystalliza tion. A single resonance was observed in the 'P NMR spectrum of 5 at 25.6 ppm. The quantitative rearrangement of 4 to 5 was followed by ''P NMR. Structure Determination of 3 and 4 by NMR Both 4 and 5 contain two groups of atoms derived from dibenzoylmethane molecules. The signals of the atoms forming the backbones of these units must be identified and assigned in order to determine the structures of these products. However, each com pound contains 9 quaternary carbon atoms and 17 different types of CH groups. The protons of the CH groups in the backbone play a key role in the analysis. Their 'H NMR signals are easily recognized because these protons do not couple with other hydrogen nuclei. The 1 ’C resonance of the carbon atom to which each of these protons are bonded was located in a 2D 13C,*H — chemical shift correlated NMR spectrum [10], The signals of carbon atoms within ca. three bonds of each proton were then iden tified by recording 2 D 1 3C, 'H-chemical shift correlated NMR spectra optimized for long range / c . h couplings (LR-HETCOSY) [10]. Analysis of the NMR spectra of 4 Unexpectedly, the l?C NMR spectrum of 4 meas ured at —30 °C has no signals in the carbonyl region. The signals of the protons on C-4 and C -8 (num bering scheme in Fig. 1), the central methine carbon atoms of the original diketone units, are a doublet at (3h(H-4) = 6.27 ( 7p.h = 32 Hz) and a sharp singlet at