Selective [3 + 2] C–H/C–H Alkyne Annulation via Dual (Distal) C(β, δ)–H Bond Activation Relay: A Novel Therapeutic Quinazolone-Tethered Benzofulvenes for Oral Cancer

Abstract

In contrast to proximal C–H bond activations, distal C–H bond activation is fundamentally more challenging and requires distinctly specialized directing partners or techniques. In this context, we report an unprecedented dual (distal) β-C(benzylic)–H and δ-C(aryl)–H bond activation relay protocol for the chemo-, regio-, and stereoselective construction of heterocycle-tethered benzofulvenes via [3 + 2] CH/CH-alkyne annulation under palladium catalysis. The protocol overrides the more favorable [4 + 2] CH/NH annulation and does not follow the vinylic C–H bond activation pathway. Mechanistic studies provide insight into the favored cyclopalladation of key intermediates (resulting from β-C(benzylic)–H bond cleavage) through relay δ-C(aryl)–H cleavage (vs N–H cleavage) prior to reductive elimination, which is the key to desired annulation. The synthesized new chemical entities (NCEs) constitute a novel scaffold with favorable anticancer activity against oral squamous cell carcinoma (OSCC). Detailed biomolecular studies, including RNA-sequencing and analysis, indicate that these compounds (4e and 4w) arrest the cell cycle at the S-phase and target multiple cancer hallmarks, such as the activation of apoptotic pathways and impairment of mitochondrial activity simultaneously, suggesting their chemotherapeutic potential for oral cancer by addressing the complexity and adaptability of cancer cells in chorus.