The ortho‐Substituent Effect on the Ag‐Catalysed Decarboxylation of Benzoic Acids

Abstract

A combined experimental and computational investigation on the Ag-catalysed decarboxylation of benzoic acids is reported herein. The present study demonstrates that a substituent at the ortho position exerts dual effects in the decarboxylation event. On one hand, ortho-substituted benzoic acids are inherently destabilised starting materials compared to their meta- and para-substituted counterparts. On the other hand, the presence of an ortho-electron-withdrawing group results in an additional stabilisation of the transition state. The combination of both effects results in an overall reduction of the activation energy barrier associated with the decarboxylation event. Furthermore, the Fujita-Nishioka linear free energy relationship model indicates that steric bulk of the substituent can also exert a negative effect by destabilising the transition state of decarboxylation.

Palladium‐Catalyzed Decarbonylative Trifluoromethylation of Acid Fluorides

“…Notably, the acid fluoride derivative of 3,4‐dimethoxybenzoic acid ( 1 h ), which is the end‐product from Lignin valorization,17 was also successful. The highest yields were obtained for those substrates that possessed otho ‐substitution to the COF functionality,18 in line with reactivity trends previously seen for metal‐catalyzed decarbonylations of other carbonyl derivatives,1j, 19 or trifluoromethylations 20. For example, the slight modification from para ‐ to ortho ‐linkage of the biphenyl acid fluoride 1 a (to 1 b ) resulted in a two‐fold increase in yield.…”

Palladium‐Catalyzed Decarbonylative Trifluoromethylation of Acid Fluorides

“…Notably, the acid fluoride derivative of 3,4‐dimethoxybenzoic acid ( 1 h ), which is the end‐product from Lignin valorization, was also successful. The highest yields were obtained for those substrates that possessed otho ‐substitution to the COF functionality, in line with reactivity trends previously seen for metal‐catalyzed decarbonylations of other carbonyl derivatives, or trifluoromethylations . For example, the slight modification from para ‐ to ortho ‐linkage of the biphenyl acid fluoride 1 a (to 1 b ) resulted in a two‐fold increase in yield.…”

The use of carboxylic acids as traceless directing groups for regioselective C–H bond functionalisation

“…25 In light of this, it is proposed that benzoic acids bearing electronwithdrawing substituents are more reactive than those bearing electron-donating substituents as they can better stabilise this Scheme 2 Copper-catalysed protodecarboxylation of aromatic carboxylic acids. a GC yield.…”