Ortho-Palladation of (Z)-2-Aryl-4-Arylidene-5(4H)-Oxazolones. Structure and Functionalization

Abstract

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 3 CHCl 3 gives the six-membered cyclopalladated dinuclear complex [Pd(μ-Br)-(o-C 6 H 4 CHdCNC(O)OCPh)] 2 (7). The reaction of 7 with PPh 3 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 PPh 2 Me gives mononuclear 8, which incorporates two phosphines as a results of the cleavage of the μ-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 C 6 H 4 -2-Br-CHdCNC(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 C 6 H 4 -2-OAc-CHdCNC(O)OCPh (20) through C-O coupling. When treatment of 7 with PhI(OAc) 2 is performed in MeOH or EtOH, the oxazolones C 6 H 4 -2-OR-CHdCNC(O)OCPh (R = Me (18), Et (19)) are obtained. The reaction of 7 with CO in alcohols ROH gives cleanly the oxazolones C 6 H 4 -2-CO 2 R-CHdCNC(O)OCPh (R = Me (21), i Pr (22)) through CO migratory insertion into the Pd-C bond and further nucleophilic attack of the ROfragment.

Terpyridine–Porphyrin Hetero‐Pacman Compounds

“…Palladium is situated in a typical square‐planar coordination sphere with the two triphenylphosphine ligands assuming trans positions. The CPd (2.015 Å), PdI (2.673 Å), and PdP bonds (2.316 and 2.341 Å) are in agreement with known structures, for which lengths between 1.99–2.03 Å for the CPd bond, 2.66–2.70 Å for the PdI bond, and 2.31–2.35 Å for the PdP bond can be found 63–66. A similar result is observed for the bond angles around the central palladium atom of 6 .…”

Orthopalladation of GFP‐Like Fluorophores Through C–H Bond Activation: Scope and Photophysical Properties

“…Surprisingly, the use of transition metals for rigidification of imidazolones has never been attempted and, in the case of oxazolones, only some few cases using Pd as metal have been reported , . Moreover, the photophysical properties of the oxazolones once cyclopalladated remains totally unexplored.…”

Reactions of m-chloroperoxybenzoic acid with dimeric cyclopalladated complexes derived from 2-phenyl-2-oxazolines

“…Reactions at the C-Pd bond of cyclopalladated complexes (CPCs) [1][2][3][4][5] (e.g., phosphination [6][7][8][9][10], chlorination [11][12][13][14], iodination [15][16][17][18][19], bromination [15,16], acetoxylation [20][21][22][23][24][25] and other transformations [15,[26][27][28][29][30][31]) represent an attractive method for highly regioselective functionalization of organic compounds. These Pd-mediated transformations are gaining importance as a synthetic method, providing access to new organic and organometallic compounds not readily available by other methods.…”