ORGN 448 |
| The development of transition metal catalysts for regioselective synthesis of vinyl phosphonates/ phosphinates has been a challenge for synthetic chemists. In this context, we herein report three protocols for palladium-catalyzed regioselective addition of ethyl phenylphosphinate [(EtO)PhP(O)H] to terminal alkynes, which furnishes either linear (anti-Markovnikov) or branched (Markovnikov) adduct, depending on the ligand or the solvent. The reaction of phenylacetylene with ethyl phenylphosphinate in toluene was branched selective (99% selectivity) in the presence of palladium acetate (5 mol %) and 1,2-bis(diphenylphosphino)ethane (dppe, P/Pd = 3). On the contrary the same reaction using palladium acetate / tri-tert-butylphosphine (P/Pd = 3) afforded the linear adduct preferentially and the selectivity was enhanced upon increasing the P/Pd up to 20 (90% selectivity). The reaction run in ethanol using palladium acetate / triphenylphosphine (P/Pd = 3) was also linear selective (82% selectivity) although it was somewhat slow. Further details of the ligand effect and the applicability of the recipe to other acetylenes will be discussed.
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Modern Acetylene Chemistry
8:00 PM-10:00 PM, Tuesday, 12 September 2006 Moscone Center -- Hall D, Poster
Sci-Mix
Division of Organic Chemistry |
