A Prodigious Behavior of Cycloalkyl Carboxylic Acid to Access 2D Space from 3D Space via Multifold C-H Activation

The dehydrogenation chemistry has long prevailed in the paradigm of organic synthesis. More common with carbonyl compounds, many classical reactions evolved around it. The emergence of the transition metal catalysis redefined the dehydrogenation chemistry with strategies such as transfer dehydrogenation, C-H activation and single electron transfer processes. These strategies have been extended to enable multiple dehydrogenations that had led to aromatization depending on the substrate class. On a contrary, dehydrogenative transformations of aliphatic carboxylic acids offers substantial challenges. Engineered ligands in conjunction with metal catalysis can effectuate the dehydrogenation in carboxylic acids initiated by C-H activation with subsequent functionalization or vice versa; however, the reactivity and product formation vary with the substrate structure. Herein, we have developed a catalytic system that enables cyclohexane carboxylic acid to undergo multifold C-H activation to furnish olefinated arenes implying 3D to 2D conversion and thus, completely bypassing the lactone formation, showcasing a display of the change in reactivity of aliphatic carboxylic acids. The reaction occurs via a tandem dehydrogenation-olefination-decarboxylation-aromatization sequence which has been proved by various control experiments and isolation of key intermediates. For cyclopentane carboxylic acid which are reluctant to aromatization, the same catalytic system allows controlled dehydrogenation to provide difunctionalized cyclopentene derivatives via a tandem dehydrogenation-olefination-decarboxylation-allylic acyloxylation reaction sequence. The transformation is amenable to diversify carboxylic acids to be transformed to molecules of new identity having applications in different fields thus underscoring the im-portance.