Palladium‐Catalyzed Hydrobenzylation of ortho‐Tolyl Alkynyl Ethers by Benzylic CH Activation: Remarkable Alkynoxy‐Directing Effect

Abstract

It's selective: The title reaction involves palladium(0)-catalyzed insertion of C≡C bonds into benzylic C(sp(3))-H bonds, thus providing efficient access to 2-methylene-2,3-dihydrobenzofurans, which transform into benzofurans upon treatment with a weak acid (e.g., AcOH) and electrophiles. The alkynoxy group serves as a directing group in promoting C-H bond functionalization.

Collaborative Interaction of Carbon–Carbon Unsaturated Bond Groups with Transition-metal Catalysts for C–H Bond Functionalization

“…2-Benzylic CH bonds at the alkynoxyarenes are smoothly activated in the presence of Pd(OAc) 2 , PCy 3 , and Zn as a reductant to form Pd(0) and proceed hydrobenzylation to give 2-silylmethylene-2,3-dihydrobenzofurans (Scheme 16). 21 The Pd(dba) 2 , PCy 3 , and acetic acid catalytic conditions also afford the same product, albeit in a slightly lower yield. Based on the latter catalytic conditions, the non-activated C(sp 3 )H bond in the tert-butyl group can be activated in the presence of Pd(dba) 2 , PnBu 3 , and pivalic acid catalysts to form chromane derivatives (Scheme 17).…”

Activation of stable σ-bonds for organic synthesis

“…Taking advantage of the conjugate exo-methylenes, the Diels-Alder reaction of the cycloadducts with N-phenylmaleimide takes place smoothly to give tetracyclic structures with high stereoselectivity (Scheme 19) [18]. Upon treatment with Pd(II) and Zn catalyst system, o-tolyl TIPS-ethynyl ethers undergo ring closure to give 2-silylmethylene dihydrobenzofurans possibly through benzylic γ-C-H activation (Scheme 20) [19].…”

Copper‐Catalyzed Benzylic C—H Functionalization, Oxidation and Cyclization of Methylarenes: Direct Access to 2‐Arylbenzothiazoles

“…Later, Li developed a potassium iodide‐catalyzed three‐component synthesis of quinazolines via benzaldehyde intermediate. Hiyama and Matsuzaka reported a direct dehydrative condensation of benzylic C—H bonds. A practical Brønsted acid promoted‐benzylic C—H functionalization of 2‐alkylazaarenes and nucleophilic addition to nitroso compounds was also developed by Yang .…”