Construct of chemical bonds via the transition metal catalyzed chelation-assisted
C-H functionalization reaction is one of the efficient methods in organic synthesis. This type of reaction is a highly atom-, step-economical and environmentally friendly manner. Heteroatoms such as nitrogen or oxygen containing chelating groups are needed for this type of reaction.1 The C-H bond activation by using strong nitrogen containing chelating group is quite easy and well documented in the literature. But, the activation in the presence of a weak oxygen containing directing group is very challenging due to the formation of thermodynamically a less stable metallacycle intermediate.1 In this seminar, I would like to discuss the C H bond functionalization of weak chelating group assisted substituted aromatics or alkenes with carbon-carbon π-components in the presence of a ruthenium/rhodium catalyst.
We have investigated the reaction of benzoic acids with allylic acetates in the presence of a Ru(II) complex. The catalytic reaction was done in the redox-neutral version. During the investigation, we have observed three different type of products (Z)-3-ylidenephthalides, ortho-allylated and ortho-vinylated benzoic acids in the reaction of substituted benzoic acids with allylic acetates.2a The functionalization of arylacetamide is challenging due to its intrinsic ability to undergo tautamerizable nature, unfavourable six-membered metallacycle formation, and the weak coordinating ability of acetamides. In this regard, we have disclosed a Rh(III)-catalyzed redox-neutral C-H vinylation/allylation of weak coordinating arylacetamides with allylic acetates.2b Further, we have demonstrated ortho-alkylation of weak coordinating arylacetamides with acrylates catalysed by a Ru(II) complex in a redox-neutral manner.2c A similar type of reaction was examined with different metals. Interestingly, in the aerobic Rh(III)-catalyzed reaction, we have observed ortho-alkenylated arylacetamides in the reaction of substituted arylacetamides with activated alkenes.2d The metal-catalyzed C−H olefination of substituted aromatics with alkenes is a highly efficient method to synthesize arylated alkenes in a highly regio- and stereoselective fashion. For this kind of transformation, only activated olefins are widely used. Nevertheless, the C−H olefination of substituted aromatics with unactivated olefins is very challenging and not well explored in the literature due to the lower reactivity and unbiased nature. In this regard, we have developed a Rh(III) catalyzed C−H olefination of aromatic/vinyl carboxylic acids with unactivated olefins at room temperature. The reaction provides ortho-alkenylated aromatic acids and β-C−H-olefinated acrylic acids. It should be noted that, the COOH group was not involved in the intramolecular cyclization with the alkene.2e Later, we have also demonstrated a Rh(III)-catalyzed aerobic oxidative C-H olefination of substituted arylamides with unactivated aliphatic olefins without using any external metal oxidant.2f
Reference: (1) (a) Arockiam, P. B.; Bruneau, C.; Dixneuf, P. H. Chem. Rev. 2012, 112, 5879. (b) Manikandan, R.; Jeganmohan, M.; Chem. Commun. 2017, 53, 8931 (2) (a) Jambu, S.; Tamizmani, M.; Jeganmohan. M. Org. Lett. 2018, 20, 1982. (b) Jambu, S.; Jeganmohan. M. Org. Lett. 2019, 21, 5655. (c) Jambu, S.; Sivasakthikumaran, R.; Jeganmohan. M. J. Org. Chem. 2019, 84, 3977. (d) Jambu, S.; Sivasakthikumaran, R.; Jeganmohan. M. Org. Lett. 2019, 21, 1320. (e) Jambu, S.; Jeganmohan, M. Org. Lett. 2020, 22, 5057. (f) Jambu, S.; Shambhavi, C-N.; Jeganmohan, M. manuscript under preparation.