Hydrophosphorylation, alkenes

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, 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. 

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. 

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). 

Addition reactions. Under oxygen fi-propylcatecholborane catalyzes anti-Markovnikov hydrophosphorylation of 1-alkenes. 

The reaction of triethyl phosphite with maleic anhydride has been re-investi-gated. The product is not the dimeric phosphorane (11), but the ylid (12). Reactions of alkyl or aryl diphenylphosphinites with 1-nitro-l-alkenes have been studied in detail. Radical ion-pairs are involved as shown by e.s.r. and P CIDNP experiments. Allene may be hydrophosphorylated in a radical-initiated process to give allyl- and isopropenyl-phosphonates. A phosphorane (14) has been observed during the reaction of ethyl diethylthiophosphinite (13) with methacrylic acid. ... 

Hydrophosphorylation of alkenes has been regarded as a rather difficult reaction. Tanaka discovered that efficient hydrophosphorylation of simple alkenes and cyclic alkenes is possible by using the five-membered cyclic phosphonate 52. The reaction of 1-octene with 52 proceeded at 100 "C to afford the linear phosphonate 53 in 89 % yield. Regioselectivity depends on the nature of the alkenes, and the branched phosphonate 54 was formed by the reaction of styrene. DPPB was found to be a suitable ligand [29]. Hydrophosphination of styrene with diphenylphos-phine (55) proceeded regioselectively by using phosphine-free Pd catalyst to afford 2-phenylethyl(diphenyl)phosphine (56) [30]. 

Mechanistically, they proposed that Ag first reacted with PhjPfO) to form the crucial active intermediate, which promotes the reaction. Worthy of note that this is the first time for the hydrophosphorylation of alkenes via silver salt to be catalyzed. 

Hydrophosphorylation of alkenes and alkynes with phosphinic acid derivatives such as alkyl phosphinates [H2P(0)(0R)] and anilinium phosphinate [PhNH3 0P (0)H2] is successfully catalyzed by palladium complexes, in particular those ligated by xantphos and dppf [25]. Polymer-botmd palladium catalyst 11 has proved to catalyze the same reactions with phosphinic acid to give good yields, although the... 

Pd] = PdM62(PPh2Cy)2 R = Ph (a-isomer >95%) Scheme 8.15 Pd-catalyzed hydrophosphorylation of alkenes... 

It was possible to carry out hydrophosphorylation of non-activated alkenes only with cyclic five-membered P-H substrate using cis-PdMcaLa as catalyst precursor (Scheme 8.15) [77]. Neither six-membered analogs of the substrate, nor non-cyclic dialkyl phosphites were active in this catalytic addition reaction. 

Tayama O, Nakano A, Iwahama T, Sakaguchi S, Ishii Y (2004) Hydrophosphorylation of alkenes with dialkyl phosphites catalyzed by Mn(lll) under air. J Org Chem 69 5494-5496... 

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