Synthesis of Phenolic Compounds via Palladium Catalyzed C−H Functionalization of Arenes

Abstract

Phenol and its derivatives are extremelyu seful compoundsi no rganic synthesis, medicinal chemistry and material sciences. The synthesis of phenols involvings elective construction of the CÀOb ond at aC ÀHb ond of arenes using transition-metalc atalysis represents the most appealing strategy.I ndeed, active research is currently going on for the synthesis of valuable phenolic compoundsu sing at ransition-metal-catalyzed CÀHf unctionalization strategy.T his short review summarizes recent advances on palladium-catalyzed CÀOb ond forming reactions that enable direct access to phenolic compounds. These catalytic reactions proceed either via CÀHe sterification with trifluoroacetic acid/trifluoroacetic anhydridef ollowedb yi ns itu hydrolysis of the ester or via direct CÀHh ydroxylation.Abrief analysis of substrate scope and limitation, reaction mechanism as well as synthetic utility of these reactions has been included.

Electrochemical Hydroxylation of Electron‐Rich Arenes in Continuous Flow

“…The traditional methods for arene hydroxylation rely on transition-metal catalysis and often require harsh reaction conditions. [4][5][6] Out of different possible options to hydroxylate arenes, [7,8] oxygen [9,10] and H 2 O 2 [11][12][13] are the most frequently used oxidative hydroxylation agents. Lutz Ackerman and Yu Rao have demonstrated methods in which trifluoroacetic acid was used as a hydroxyl group source in transition-metal catalyzed oxidation of arenes in the presence of stoichiometric oxidants (Scheme 1A).…”

Recent Advancements on Transition‐Metal‐Catalyzed, Chelation‐Induced ortho‐Hydroxylation of Arenes

“…[11b] [14] Recently, Guin group has published an elegant review only on Pd catalyzed CÀ H hydroxylation of arenes. [15] In the last few decays, numerous developments in the construction of CÀ C, CÀ O, CÀ N, CÀ P, CÀ S and CÀ X bonds have been reported using palladium catalysts. [16] Because of its versatility in mechanistic path such as Pd(0)/Pd(II), Pd (II)/Pd(IV), Pd(II)/Pd(0) and Pd(II)/Pd(II), compatibility with different directing groups and capability for regeneration, palladium can facilitate the CÀ H bond activation reactions through abstraction of ortho-proton to the directing groups.…”

“…Few review articles have been published on transition metal catalyzed hydroxylation of arenes in last few years. [11b][14] Recently, Guin group has published an elegant review only on Pd catalyzed C−H hydroxylation of arenes [15] . In the last few decays, numerous developments in the construction of C−C, C−O, C−N, C−P, C−S and C−X bonds have been reported using palladium catalysts [16] .…”

Alkenylation of ortho-palladated phenylglycine: synthesis of stilbene derivatives and 3-aryl-isoquinoline-1-carboxylates

“…The functionalisation of C-H bonds mediated by transition metals, especially palladium, is now a valuable and firmly established synthetic tool that allows the transformation of inert C-H bonds into new C-C or C-heteroatom bonds with high selectivity, in some cases under mild conditions. [18][19][20][21][22][23][24][25][26][27][28][29] This ability to transform raw precursors into valuable modified products includes, of course, fragile substrates such as amino acids and peptides. [30][31][32][33] In this respect, in the last few years there has been increasing interest in the C-H functionalisation of αphenylglycine and some of its derivatives.…”