Carboxylic Acids as Traceless Directing Groups for Formal meta‐Selective Direct Arylation

Abstract

Spurlos: Bei der ersten meta‐selektiven direkten C‐H‐Arylierung mit Iodarenen als Kupplungspartnern (siehe Schema, EWG=elektronenziehende Gruppe) werden Carbonsäureeinheiten als temporäre Steuergruppen genutzt, die während der Reaktion abgespalten werden, ohne eine Spur in den gebildeten Biarylprodukten zu hinterlassen.

Pd(II)-catalysed meta-C–H functionalizations of benzoic acid derivatives

“…Desired meta -functionalized products were obtained regardless of the substitution patterns and steric biases of the substrates. Notably, the challenging tri-substituted substrates were tolerated, which was not observed in previous transition-metal catalysed meta -C–H functionalizations 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 . Importantly, the new protocol was compatible with molecular oxygen as the terminal oxidant.…”

“…So far only a limited number of approaches are available for addressing meta -C–H functionalizations of arenes 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 . These approaches include inherent substrate control via steric and/or electronic factors 28 29 30 31 32 33 34 35 , chelating group-assisted Cu(II)-catalysed arylation 36 37 , ruthenium(II) complex facilitated meta -C–H functionalizations 38 39 40 41 42 43 , the use of transient norbornene mediator 44 45 and formal meta -C–H functionalizations utilizing traceless directing groups 46 47 48 49 50 51 . Another unique method is the use of nitrile-based templates for meta -C–H functionalizations of electron-rich arenes, such as hydrocinnamic acids and phenylacetic acids, which was pioneered by the group of Yu 54 55 56 57 58 59 60 61 62 63 .…”

A decarboxylative approach for regioselective hydroarylation of alkynes

“…Although the strategy of utilizing carboxyl functionality as a removable ortho-directing group has been reported as part of a tandem sequence or in a separate step [35][36][37][38][39][40][41][42][43][44][45][46][47] , the decarboxylative C-H alkenylation with alkynes has not been reported. The dominant majority of the reported decarboxylative C-H functionalization processes require high reaction temperatures (130-170°C) and stoichiometric Ag(I) or Cu(II) salts to promote decarboxylation.…”

Synthesis of Aryl Ethers from Benzoates through Carboxylate‐Directed CH‐Activating Alkoxylation with Concomitant Protodecarboxylation

“…The viability of a reaction concept that combines an ortho alkoxylation with a concomitant decarboxylation is further supported by the documented ability of aromatic carboxylate groups to direct other types of CÀH functionalization into their ortho position, [21] for example, as described by Yu et al [22] Furthermore, Satoh, Miura, and Larrosa and their respective co-workers described C À H arylations of aromatic carboxylic acids with subsequent removal of the carboxylate directing group by in situ protodecarboxylation. [23] Our mechanistic outline for an efficient decarboxylative ortho alkoxylation process of benzoates is shown in Scheme 2. It consists of a silver/copper-mediated oxidative ortho alkoxylation cycle of the benzoate linked with a decarboxylation cycle.…”