Room-Temperature Rhodium–Silver Cooperative C–H Alkynylation of Indoles in Bio-Based Cyrene: A Green Protocol with Mechanistic Insights from DFT Studies

Transition metal-catalyzed C-H activation reactions are desirable as they fulfill several principles of green chemistry. However, these reactions often use toxic and volatile organic solvents, significantly hampering the sustainability of the C-H activation strategy. In this work, we demonstrate the use of biobased Cyrene as the solvent for the rhodium(III)-catalyzed C-H alkynylation of indoles. The reaction was performed at room temperature with a shorter reaction time. Detailed mechanistic studies were conducted to understand the reaction mechanism. Supported by DFT calculations and experimental studies, a plausible catalytic cycle was proposed, involving α-halogen elimination and silyl transfer as the key steps in the C-H alkynylation. The rhodium(III)-catalyzed C-H alkynylation in Cyrene media has been studied for the robustness of the reaction conditions by evaluating its reaction-condition-based sensitivity. Furthermore, the green chemistry metrics calculations suggested that the developed protocol is highly efficient and eco-friendly.