Mechanistic Studies of Pd‐Catalyzed Regioselective Aryl CH Bond Functionalization with Strained Alkenes: Origin of Regioselectivity

Abstract

Mechanistic studies of a palladium-catalyzed regioselective aryl C-H functionalization of 2-pyrrole phenyl iodide with norbornene are presented. Kinetic and spectroscopic analyses together with crystallographic data provide evidence for intermediates in a proposed stepwise mechanism. On the basis of the mechanistic studies, the origin of the regioselectivity is due to a ligand exchange between I(-) and HO(-) on the norbornyl palladium complex. These mechanistic studies also implicate that either alkoxide or water is responsible for the formation of the palladacycle, but a reversible ring-opening-ring-closing process of the palladacycle with HX can retard the rate of reaction of a key intermediate. The significant aspects of the proposed mechanism are discussed in detail.

Gold(iii)–arene complexes by insertion of olefins into gold–aryl bonds

“…The presence of the gold( iii ) center also affects the ortho -CH signals, one of them being shifted to high field by about 10 ppm ( δ 124.1 and 135.6 ppm). These spectroscopic data are strongly reminiscent of those observed by Cheng and Catellani for related neutral Pd( ii )–arene complexes 27–29 and suggest η 2 -coordination of the phenyl ring to gold( iii ). Some of these Pd( ii )–arene complexes have been crystallographically characterized and their bonding situation has been thoroughly investigated.…”

“…Some of these Pd( ii )–arene complexes have been crystallographically characterized and their bonding situation has been thoroughly investigated. 27–29 …”

Palladium‐Catalyzed Heteroarylation and Concomitant ortho‐Alkylation of Aryl Iodides

“…We prepared ap utative palladacycle A [18] of the catalytic cycle (Scheme 2) and then subjected it to the coupling conditions with benzoxazole (Scheme 5a). In the presence Scheme 2.…”

Dehydrogenative Carbon–Carbon Bond Formation Using Alkynyloxy Moieties as Hydrogen‐Accepting Directing Groups

“…Substrates with acyclohexyl, methyl, or phenyl group instead of the tert-butyl group attached to the ethynyl moiety were not suitable for this reaction. [12] These results suggest that abulky substituent on the ethynyl carbon atom is necessary for effective double C À Hc leavage.T he presence of para-, meta-, and ortho-substituted aryl groups in the TIPS ethynyloxy moiety did not hamper the reaction (entries [8][9][10][11][12]. Silylethynyl 4-biphenyl ether 1i afforded 3i in 78 %y ield (entry 12);t he molecular structure of 3i was confirmed by single-crystal X-ray diffraction.…”