Ortho-Palladation of (<i>Z</i>)-2-Aryl-4-Arylidene-5(4<i>H</i>)-Oxazolones. Structure and Functionalization
作者:Gheorghe-Doru Roiban、Elena Serrano、Tatiana Soler、Maria Contel、Ion Grosu、Carlos Cativiela、Esteban P. Urriolabeitia
DOI:10.1021/om901068f
日期:2010.3.22
Ortho-palladated complexes of (Z)-2-aryl-4-arylidene-5(4H)-oxazolones have been prepared through oxidative addition. The reaction of (Z)-2-phenyl-4-(2-bromobenzylidene)-5(4H)-oxazolone (4) with Pd-2(dba)(3)center dot CHCl3 gives the six-membered cyclopalladated dinuclear complex [Pd(mu-Br)(o-C6H4CH=CNC(O)OCPh)](2) (7). The reaction of 7 with PPh3 gives dinuclear 9, which incorporates one phosphine per Pd atom through cleavage of the Pd-N bond, and preserves the bromide bridging system. However, reaction with PPh2Me gives mononuclear 8, which incorporates two phosphines as a results of the cleavage of the mu-Br system and N displacement. In contrast, the reaction of 7 with pyridine gives complex 12 due to Simple cleavage of the Br bridge, leaving the N-bonding intact. Therefore, three different reaction pathways have been characterized. The reactivity of the Pd-C bond in 7 has also been examined, and functionalized oxazolones can be obtained. The reaction of 7 With PhI(OAc)(2) in acetic acid gives the starting oxazolone C6H4-2-Br-CH=CNC(O)OCPh (4), through the presumed oxidation of the Pd center and C-Br bond formation by reductive coupling. In contrast, the reaction of the acetate dimer 14 with PhI(OAc)(2) in acetic acid gives C6H4-2-OAc-CH=CNC(O)OCPh (20) through C-O coupling. When treatment of 7 with PhI(OAc)(2) is performed in MeOH or EtOH, the oxazolones C6H4-2-OR-CH=CNC(O)OCPh (R = Me (18), Et (19)) are obtained. The reaction of 7 with CO in alcohols ROH gives cleanly the oxazolones C6H4-2-CO2R-CH=CNC(O)OCPh (R = Me (21), Pr-i (22)) through CO migratory insertion into the Pd-C bond and further nucleophilic attack of the RO- fragment.