Hydrophosphinations regioselectivity

Organolanthanide-catalyzed intermolecular hydrophosphination is a more facile process than intermolecular hydroamination. The reaction of alkynes, dienes, and activated alkenes with diphenylphosphine was achieved utilizing the ytterbium imine complex 9 (Fig. 8) as catalyst [185-188]. Unsymmetric internal alkynes react regioselectively, presumably due to an aryl-directing effect (48) [186]. 

Markovnikov or anti-Markovnikov selectivity in hydrophosphination of alkynes (Scheme 1) depends on the metal catalyst and reaction conditions it is thought to be controlled by the regioselectivity of insertion of an alkyne into an M-H or M-P bond. 

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]. 

Keywords Alkynes, iodine/hydrophosphine binary system, CDCI3, room temperature, regioselective hydroiodination, Markovnikov-type addition, vinyl iodides... 

Product selectivities differ between the different catalyst systems. In all cases, reactions are regioselective giving anii-Markovnikov or 2,1-addition of the phosphine to the least hindered end of the unsaturated system (Scheme 12a). For example, in the hydrophosphination of styrenes this selectivity can be attributed to the organization of the transition state to P-C bond formation. In the case of the 2,1-insertion of styrene into the Ca-P bond the phenyl group may stabilize the adjacent anionic center. In the case of a 1,2-insertion no such stabilization exists [106]. 

The hydrophosphination of alkynes under radical conditions has been reported [457, 458]. One example of this chemistry used AIBN to promote the addition of diphe-nylphosphine to terminal and internal alkynes (Scheme 4.292) [458]. The reactions were carried out under argon and without the addition of a solvent. After stirring for 10-156 h, moderate to excellent yields of the addition products were isolated. It should be noted that the authors successfully carried out the addition reaction using a mercury lamp to promote the radical addition reaction. For those versions of the chemistry, typical reaction times were 3-5 days and similar isolated yields were reported. While the chemistry was highly regioselective and generally formed the anti-Markovnikov addition products, only moderate... 

Regioselective transformation was observed leading to the ) -adduct as a sole product. Involvement of the rr-allylic intermediate (similar to Pd-catalyzed hydroamination of styrene) in the catalytic cycle was excluded, since the a-adduct was not formed in Ph2P-H addition to styrene and vinyl pyridine [126]. The plausible catalytic cycle of alkenes hydrophosphination involves oxidative addition of the phosphine to Ni(0) leading to the formation of H-Ni-P complex, followed by alkene insertion into the Ni-H bond and reductive elimination (Scheme 8.45). 

The first example of Pd and Ni-catalyzed hydrophosphination of terminal and internal alkynes was reported in 2001 (Scheme 8.51) [134]. Regioselectivity of the reaction depended on the catalytic system used and the nature of the alkyne. Hydrophosphination of phenylacetylene in acetonitrile solution in the presence of Pd(0) complexes led to the -adduct, while Ni(acac)2 in the presence of (EtO)2 P(0)0H gave nearly pure a-adduct (a / = 95 5). 

Ogawa et al. have reported a novel regioselective hydrophosphination of terminal alkynes with diphosphine in the presence of Pd catalyst [135]. Surprisingly, the reaction resulted not in the corresponding bisphosphination product, but in the formation of Markovnikov-type hydrophosphination product [135]. Rh-catalyzed transformation in the presence of hydrosilanes afforded anti-Mark-ovnikov-type hydrophosphination product [136]. 

Mimeau D, Delacroix O, Gaumont A-C (2003) Regioselective uncatalysed hydrophosphination of alkenes a facile route to P-alkylated phosphine derivatives. Chem Commun 2928-2929... 

J6r6me F, Monnier F, Lawicka H, Derien S, Dixneuf PH (2003) Ruthenium catalyzed regioselective hydrophosphination of propargyl alcohols. Chem Commun 696-697... 

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