Dialkyl arylphosphonates

Dialkyl arylphosphonates and alkenylphosphonates are prepared by the coupling of halides or triflates with the dialkyl phosphonate 783[64l-643]. 

Et or Bu) and the phosphonation of iodoaromatics with dialkyl phosphonates, although in this case with poorer yields (better results of the dialkyl arylphosphonates are obtained by photostimulation). Chemical oxidation (using AgNO -peroxodi-sulphate) and anodic oxidation of aromatics in the presence of trialkyl phosphites produces dialkyl arylphosphonates in good yields. The Cul-catalysed arylation of dialkyl (cyanomethyl)-phosphonates affords dialkyl (a-cyanobenzyl)phosphonates. ... 

A Michaelis-Becker approach using the sodium salt of dialkyl phosphites has been successful for the formation of C-P bonds to aromatic rings.184 Reaction of the dialkyl phosphite in DMF with the appropriate diaryliodonium halide provides the corresponding dialkyl arylphosphonate in good yield (81 to 93%). This approach to the arylphosphonate esters proceeds in superior yield under relatively mild conditions and therefore is one to be accorded serious consideration for the preparation of such materials. 

Similarly, copper salts (cupric and cuprous) facilitate the reaction of aryl halides with trialkyl phosphites in the formation of dialkyl arylphosphonates under conditions like those found in nickel systems.37-39 Again, the copper salts appear to undergo an initial reaction with the phosphites to form a complex that subsequently undergoes reaction with the aryl halide. The requirement for copper is also similar to that for nickel saltstonly a catalytic amount is needed. Further, a preference among halides on the aromatic ring is noted iodide is replaced preferentially to other halides (Figure 6.10).40... 

Ohmori, FI., Nakai, S., and Masui, M., Formation of dialkyl arylphosphonates via arylation of trialkyl phosphites, ]. Chem. Soc., Perkin I, 2023, 1979. 

Fourth, the present procedure bears a resemblance to the photochemical reaction of aryl iodides with trialkyl phosphites, by means of which several dialkyl arylphosphonates have been prepared.13 However, prolonged irradiation (>24 hours) in quartz vessels was employed. 

Table 4 Yields of Dialkyl Arylphosphonates Formed in the Photostimulated Reaction of Dialkyl Phosphite Ions with Aryl Halides ArX + (ROhPO" - (RO>2P( —Q)Ar ...

The palladium-catalysed cross-coupling of aryl halides or vinyl halides with dialkyl phosphonates (31) to yield dialkyl arylphosphonates and dialkyl vinylphosphonates, respectively, was first reported by Hirao and co-workers 69 the halides used most frequently are bromides and the reaction is stereospecific with haloalkenes. Subsequently, analogous reactions of alkyl alkylphosphinates (32), alkyl arylphosphinates (32), alkyl phosphinates (33), and secondary phosphine oxides (34), replacing [P—H] bonds with [P—C] bonds to yield various phosphinates and tertiary phosphine oxides, have been developed (Figure 7.1). Alkyl phosphinates (33) may be mono- or diarylated as desired by the selection of appropriate conditions. Aiyl and vinyl triflates have also found limited... 

Hall, N., and Price, R., The copper-promoted reaction of o-halogenodiaiylazo-compounds with nucleophiles. Part 1. The copper-promoted reaction of < -bromodiarylazo-compounds with trialkyi phosphites. A novel method for the preparation of dialkyl arylphosphonates, J. Chem. Soc., Perkin Trans. 1, 2634, 1979. 

The light-induced reactions of fluoro-, chloro-, and bromo-naphthalenes have been studied in the nucleophilic solvents methanol and diethylamine.83 The fluoro-derivative yields substituted products from the naphthalene singlet state, but the other halogenonaphthalenes react from the Tx state to give mainly the radical products naphthalene and binaphthyl, although some substitution is observed. Attempts to quench the reactions led to anomalous behaviour in that the quantum yields were actually increased in the presence of several potential triplet quenchers.84 85 Aryl iodides have been reported to react rapidly with potassium dialkyl phosphates in liquid ammonia when irradiated with 350 nm wavelength light.86 Dialkyl arylphosphonates are formed in 87—96% yield... 

Slightly unconventional modifications have been applied, occasionally with advantage, to otherwise conventional preparative reactions. Thus, the Michael-Becker reaction between dibromomethane and sodium dialkyl phosphites in solvents containing liquid ammonia is aided by exposure of the reaction mixtures to ultraviolet radiation. Dialkyl arylphosphonates are obtained in very high yield from the reaction between trialkyl phosphites and aromatic hydrocarbons when carried out in the presence of trisodium phosphate in an electrochemical system (see Organophosphorus Chemistry , Vol. 12, p. 105). The bond between phosphorus and aromatic carbon is also formed when aryl halides react with the P(0)H function in the presence of a combination of tetrakis-... 

Dialkyl arylphosphonates are also obtained from sodium dialkyl phosphites and aryl halides in the presence of Cu I in HMPTin a similar reaction, diethyl (l-cycloalkenyl)phosphonates with carbon rings having up to 12 atoms were prepared in 50—70% yields from the 1-cycloalkenyl chloride and the copper(i) adduct from triethyl phosphite. ... 

A novel route to the dialkyl arylphosphonates (34) involves the use of (l,2-propadiene)phosphonate anions with vinamidinium salts the yields vary from 5 to 83%. The use of 2-(dimethylamino)enones yields the phosphonic esters (35) in 48— 90% yields in a less-well exemplified series. ... 

A P n.m.r study has been made of the PdCl2-catalysed reactions between unactivated aryl halides and trialkyl phosphites which lead to dialkyl arylphosphonates. Several Pd-containing species have been recognised as participating in the general reaction scheme.Other applications Pd(0)-catalysis are to be found later in this Report. 

It was shown that dialkyl arylphosphonates were prepared in good yield by the reaction of aryl iodides or bromides with dialkyl H-phosphonates in the presence of triethylamine and a catalytic amount of tetrakis(triphenylphosphine)palladium [368],... 

Dialkyl arylphosphonates are synthesized by the reaction of the corresponding sodium salts of dialkyl phosphites with arylhaUdes in the presence of copper (1) iodide [369]. 

This method is also suitable for the synthesis of steric-hindered dialkyl arylphosphonates. The yields of dialkyl arylphosphonates are, however, lower than in the case where cupric iodide is used as a catalyst. 

Arbuzov and Michaelis-Becker reactions provide facile and versatile procedures for the formation of carbon-phosphorus bonds. These methods, however, are not applicable to the formation of sp hybridized carbon-phosphorus bonds. Only few methods have been reported for the syntheses of arylphosphonates and vinylphospho-nates. Direct reaction of aryl or vinyl halides with trialkyl phosphite in the presence of nickel halide requires severe reaction conditions [21,22], and the stereochemistry of vinylphosphonates has not been clarified. Synthesis of dialkyl arylphosphonates 22 [23, 24] is achieved by the palladium-catalyzed reaction (Scheme 2.12), which is called by Hirao reaction . The stereoselective synthesis of dialkyl vinylphosphonates 23 [24-26] is similarly accomplished by this method (Scheme 2.13). A variety of modified procedures have been developed recently [27-37]. 

A plausible formation path for dialkyl arylphosphonates is as follows. Palladium(O) species undergoes oxidative addition with aryl bromide to give the arylpalladium species, which reacts with dialkyl phosphite or phosphonate to give dialkyl arylphosphonate. 

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