Palladium-Catalyzed Regiospecific peri- and ortho-C–H Oxygenations of Polyaromatic Rings Mediated by Tunable Directing Groups

Abstract

An efficient divergent approach of Pd-catalyzed C−H oxygenation of polyaromatic rings is described. Reversible directing groups enable regiospecific peri-and ortho-oxygenation to readily access a wide array of polyaromatic phenols without preand postmanipulation of directing groups. The systematic mechanistic investigation, including deuterium-labeling experiments, palladacycle trapping, and DFT calculations, reveals that the tunable ligand-assisted C−H bond cleavage played a crucial role during the reaction process.

Overcoming peri- and ortho-selectivity in C–H methylation of 1-naphthaldehydes by a tunable transient ligand strategy

“…Collectively, we proposed a plausible catalytic cycle that is believed to be different from previous reported Pd(II)/(IV) 15 and Ir(I)/(III) 19a catalysis (Scheme 4). Starting from the formation of imine A or E, metal catalysts are incorporated to activated C−H bond and afforded 5,6-fused bicyclic or 6-membered ring at peri-position.…”

“…Previously reported F + oxidants failed to give the C–H methylation product at the peri -position. 15 Next, screening of basic additives showed that two equivalents of CsOAc gave a better yield (35%). Surprisingly, the addition of H 2 O that facilitated the solubility of trifluoroborate salt improved the yield to 43%, and yet adopting soluble methylboronate MeBF 3 (Bu 4 N) and other methylating reagents inhibited the yield (Tables S1 and S2 † ).…”

“…The only example, demonstrated by the Sorensen group, showed that the in situ formation of Schiff bases with benzaldehydes and orthanilic acids promoted ortho -C–H methylation and fluorination. 15 Our recent study has successfully extended the peri - and ortho -C–H oxygenation of polyaromatic rings. 16 Inspired by these discoveries, we envisioned that the precise site-selectivity control of proximal C–H alkylation of the naphthalene ring might be achieved via the incorporation of TDGs ( Fig.…”

Transient Directing Groups in Metal−Organic Cooperative Catalysis

“…Also, a similar hydroxylation process recently extended the scope to polyaromatic aldehydes as reported by the Zhang group using a palladium(0) precatalyst along with orthanilic acid as the transient directing mediator for the C8-selective hydroxylation of 1-naphthaldehydes through trifluoroacetoxylation and subsequent hydrolysis employing a hypervalent iodine reagent (PhI (OTFA) 2 ). [90] Interestingly, ortho-acetoxylation using related PIDA could also be achieved provided the pre-installation of the imine directing group with an aniline.…”

Palladium‐Catalyzed C8‐Oxygenation of Naphthalene Derivatives: Direct Access to Naphtholactone Skeleton

“…Another strategy, based on transient directing groups, has been lately developed by Zhang's team. [15] With this in mind, we were keen to develop a…”