Hydrophosphorylation

Because organophosphorus compounds are important in the chemical industry and in biology, many methods have been developed for their synthesis [1]. This chapter reviews the formation of phosphorus-carbon (P-C) bonds by the metal-catalyzed addition of phosphorus-hydrogen (P-H) bonds to unsaturated substrates, such as alkenes, alkynes, aldehydes, and imines. Section 5.2 covers reactions of P(lll) substrates (hydrophosphination), and Section 5.3 describes P(V) chemistry (hydrophosphorylation, hydrophosphinylation, hydrophosphonylation). Scheme 5-1 shows some examples of these catalytic reactions. 

Han and Tanaka reported that Pd(0) complexes catalyze the addition of dialkyl phosphites to terminal alkynes to give alkenylphosphonates (Scheme 5-17, hydrophosphorylation) [15]. 

R = n-CeHia, Ph, p-Tol, NC(CH2)a, HC=C(CH2)5, 3-HC=C-C6H4, 1-cyclohexenyl, SiMea Scheme 5-17 Palladium-catalyzed hydrophosphorylation of alkynes... 

Scheme 5-20 Proposed mechanism for palladium-catalyzed bis-hydrophosphorylation of alkynes...

In contrast to the other X-H additions surveyed in this chapter, there have been only a limited number of studies on the addition of P H linkages across C C (and C—O) multiple bonds. At the same time, there has been significant progress made in the development of catalytic systems for performing hydrophosphination and hydrophosphorylation compared to what was known pre-1982. 

Addition of the P—H bond of hydrogen phosphonates (R0)2P(0)H across alkynes (hydrophosphorylation) may be catalyzed using both Pd° and Pd11 complexes.196 Reaction of oct-l-yne with either (MeO)2P(0)H or (EtO)2P(0)H affords the Markovnikoff adduct (Equation (18)) as the... 

Hydrophosphorylation has recently been extended to rhodium catalysts as a route to anti-Markovnikoff products.198 Thus, 3mol.% Rh(PPh3)3Cl affords the ( )-alkenylphosphonates (R = H, Ph, -Cr,I I ]3, CH2CH2CN, SiMe3, or cyclohexenyl) in high yields (>80%) at room temperature when 4,4,5,5-tetramethyl-l,3,2-dioxaphospholane-2-oxide (74) is used as the PH source (Equation (19)).199 The rate of reaction is highly solvent dependent... 

Regioselective (Markovnikov) hydrophosphorylation of alkynes with dialkyl phosphites catalyzed by a series of Pd(0) complexes has been accomplished in excellent yield in THF solution.78 Although a variety of Pd(0) species served as catalysts, common Pd(II) species were ineffective. Several Pt(0) species were also able to catalyze the hydrophosphorylation process, but with lower efficiency. 

Han, L.-B., Mirzaei, F., Zhao, C.-Q., and Tanaka, M., High reactivity of a five-membered cyclic hydrogen phosphonate leading to development of facile palladium-catalyzed hydrophosphorylation of alkenes, /. Am. Chem. Soc., 122, 5407, 2000. 

Ovchinnikov, V.V., Lapteva, L.I., Sagadeev, E.V., and Konovalova, A.I., Thermochemistry of heteroaromatic compounds. Part 9. Enthalpies of tautomeric transformation of hydrophosphorylic compounds, Thermockim. Acta, 288,105, 1996. 

Ovchinnikov, V.V., Cherezov, S.V., Cherkasov, R.A., and Pudovik, A.N., Reactivity of cyclic and acyclic hydrophosphoryl compounds in reactions of electrophilic addition to ketene acetals and enamines, Zh. Obshch. Khim., 55,1244, 1985. 

The hydrophosphorylation of internal alkynes is somewhat slow. For instance, the reaction of 4-octyne with diethyl phosphonate resulted in 82% yield only after heating for 65 h. Only c/s-isomer was observed in NMR spectroscopy. 

Treatment of (Et0)2P(0)H with Pt(PEt3)3 cleanly forms HPt [P(0)(0Et)2](PEt3)2 via oxidative addition of the H-P bond (Scheme 20), which we believe is the initiation process of the catalysis. Mechanistic detail of the hydrophosphorylation reaction will be described for the reaction with alkene compounds. 

Nickel complexes have proved to be active for hydrophosphorylation of alkynes [17a, 25]. Not only the five-membered phosphonate but also commercially available dialkyl phosphonates readily react in the presence of... 

The hydrophosphorylation of alkenes appears to proceed via the sequence of events illustrated in Scheme 28. 

Although various substrates that have two alkene linkages or both alkene and alkyne linkages conform to the catalysis, the chemoselectivity is rather low and mixtures of products are formed. However, when bulky Me3Si is bound to the alkynyl bond in an en-yne substrate, the alkene moiety is selectively hydrophosphorylated (Scheme 34). 

More than two decades age, Hirao and coworkers briefly described a rather unsuccessful attempt of hydrophosphorylation of a diene isoprene underwent Pd-catalyzed addition of diethyl phosphonate forming diethyl 3-methyl-2-buten-l-ylphosphonate in only 10% yield even under forcing conditions (150 °C, 20 h) [29]. By using the exceptionally reactive five-mem-... 

Treatment of Cjq with lithiated secondary phosphine boranes or phosphinite boranes followed by removal of the BHj group afforded 1,2-hydrophosphorylated 27 in good yields (Scheme 3.14) [114, 117]. The phosphorus nucleophiles were generated by deprotonation of the corresponding borane complexes with Bull in THF-HMPA, and added to toluene solutions of Cjq at -78 °C. Complexes 26 are stable in air at room temperature for months. In the NMR spectrum, the proton of 26b appears... 

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