[reaction: see text] A general new method for the one-pot preparation of secondary phosphines 11 and in situ generation of their borane complexes 12 is described. This method consists of the sequential addition, at room temperature, of equivalent amounts of R(1)MgBr and R(2)MgBr to 1 equiv of the phosphorus atom donor reagent 1. Final treatment with water gives secondary phosphines R(1)R(2)PH (or the corresponding phosphine-borane complexes if treated with BH(3).THF) and the end product 6, which can be recycled.

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Anisoles 1, reacting with AlCl 3 and PCl 3 with appropriate reagent ratios, give, in good yields, the corresponding diaryl methylphosphonates 2 or the methylphoshinates 3b,c and the methylphosphine oxides 4b,c. This unexpected in situ methylphosphorylation explains the reported limited and conflicting results to obtain methoxy-substituted arylphosphonous dichloride with the same reagents. A suggested mechanism is also reported.Since the last century, the Friedel-Crafts-type reaction 1 using PCl 3 and AlCl 3 has been of interest for the direct phosphonation of an aromatic ring. However, this reaction is very sensitive to the type of substituents present on the aromatic ring. 2 In particular, very limited success and conflicting results have been reported when the reaction is carried out with anisoles. For example, anisole, 3,4 upon treatment with PCl 3 and AlCl 3 gave complex reaction mixtures depending on the quality of AlCl 3 with poor yields of methoxy-substituted arylphosphonous dichloride or phenylphosphorodichloridite and large amounts of undistillable residues:To increase the yield and the selectivity of this phosphonation reaction the use 4a of SnCl 4 and very recently the use 4c of BiCl 3 have been reported. In the past years we discovered 5 an unusual reaction of PCl 3 and AlCl 3 with thioanisoles which gave a new heterocyclic system (fused 1,2,3-benzothiadiphosphole) containing the P-PS 2 unit. Recently, the course of this unexpected diphosphonation reaction has been studied 6 and we have found that the reaction follows a complex multistep pathway which was a priori unpredictable and that the outcome of the reaction is very dependent on the ratio of the reagents and on the good quality of AlCl 3 (sublimated prior to use) which in this reaction is a true reagent and not a catalyst.Then, we thought to study again the reaction of anisoles 1 with AlCl 3 and PCl 3 , in order to find results which might explain the reported 3,4 formation of large amounts of undistillable residues. Several reactions were carried out with various molar proportions of reagents and different reaction conditions. The reaction of 1b with an appropriate ratio of the reagents, afforded a mixture containing as major products the corresponding diaryl methylphosphoryl derivatives 2b, 3b and 4b arising from an unexpected in situ methylphosphorylation (Scheme1). Scheme 1After several repeated attempts with small variations of reagent ratios and reaction conditions we could control the regiochemistry of this methylphosphorylation reaction in order to obtain mainly the diaryl methylphosphonates 2 (see Scheme 1). The best results were obtained with a 1: AlCl 3 : PCl 3 ratio of 1:0.6:1, at 70-80°C in atmosphere of dry nitrogen and without solvent (Table 1). In the case of 1c the reaction was complete in 7 h while in the other cases in about 10-15 h. A stoichiometric excess of PCl 3 was useful also to ease the stirring and the homogeneity of the reaction mixture. Compounds 2 have been fully characterised 7 by 1 H and 31 P NMR and spectral data...

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The reaction of benzothiadiphosphole 1 with an equimolar mixture of R1MgBr and R2MgBr gave intermediate A', which, after only 4-5 min, was treated with an equimolar amount of R3MgBr, giving the asymmetric phosphine PR1R2R3 in 45% overall yield (75-80% yield when R1 = R2 and 85-90% yield when R1 = R2 = R3) and the byproduct 6 in 90% yield. The treatment of 6 with PCl3 quantitatively regenerates the starting reagent 1. Treatment of the phosphines with elemental sulfur gave the corresponding sulfides.