Diphenylphosphino acetophenone

Cyclic ketals of acetophenone can be prepared directly under basic conditions by the reaction of aryl triflates, bromides or iodides with hydroxyatkyl vinyl ethers in the presence of a catalytic amount of palladium(II) acetate and 1,3-bis(diphenylphosphino)propane (DPPP).84 The example illustrated in Scheme 2.39 is noteworthy since a protected methyl ketone was appended to an arene in the presence of a reactive aldehyde functionality. 

Bromoacetophenone (100 mg, 0.5 mmol), Pd(OAc)2 (11 mg, 0.05 mmol) and PPh3 (301 mg, 1.15 mmol) were placed in a Teflon stopcock flask. The flask was then evacuated and refilled with nitrogen three times. The mixture was heated to 115 °C and the reaction was monitored by GC MS or TLC. After completion, the reaction mixture was cooled and the crude product was purified by column chromatography on silica gel using a solvent mixture of hexane-ethyl acetate (20 1) as the eluent to give 4-(diphenylphosphino)acetophenone in 44% yield as a white solid. 

Using a completely analogous procedure, the corresponding 2-(diphenyl -arsino)benzaldehyde and 2 -(diphenylphosphino)acetophenone can also be prepared. The reactive 2-(dimethylphosphino)benzaldehyde requires a modified procedure for both the Grignard addition and the hydrolysis. 

Among them, benzylmethylphenylphosphine (BMPP, I)198 and 2,3-0-isopropylidene-2,3-dihydroxy-l,4-bis(diphenylphosphino)butane (DIOP, III)146 have been employed as the most popular ligands. The best result (97.6% e.e.) for the asymmetric reduction of acetophenone to date has been achieved with 2-(2-pyridyl)-4-carbethoxy-l,3-thiazolidine (XXII)195. 

Asymmetric hydrogenation was catalyzed by ruthenium clusters containing atropoisomeric diphosphines. Catalyst precursors were Ru4(/t-H)4(CO)]o (S)-(-)-BINAP (BINAP = 2,2 -bis(diphenylphosphino)-l,l -binaphthyl) and Ru4(/t-H)4(CO)io (S)-(-)-MOBIPH (MOBIPH = 2,2 -bis(diphenylphosphino)-6,6 -dimethoxy-l,l -diphenyl). Substrates included prochiral alkenes such as tiglic acid, (Z)- and ( )-2-methylbutendioic acids, ( )-2-methylbute-noic acid, and acetophenone. Optical purities up to 38% were obtained, but most results were low ee s. 

In the context of bimetallic catalysts, an unusual cationic Ti-Rh bimetallic complex 5 exhibits an interesting cooperative effect in catalyzing the hydrosilation of acetophenone with Ph2SiH2. A weak bonding interaction between rhodium and a Cl on titanium apparently stabilizes a lower-valent Rh intermediate such that the bimetallic complex delivers a much higher hydrosilation yield than the corresponding Rh(COD) monometallic complex based on l,2-bis(diphenylphosphino)benzene. 

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