Synthesis of Polycyclic Oxazolinium Compounds from Aryloxazolines and Alkynes via Dual Photoredox/Gold Catalysis and Rhodium Catalysis

A series of polycyclic oxazolinium compounds is synthesized from various aryloxazolines with silyl-substituted alkynes and internal alkynes via two synthetic pathways. By using dual photoredox/gold catalysis, the coupling of 2-aryloxazoline diazonium compounds with silyl-substituted alkynes affords silyl-substituted polycyclic oxazoliniums in 20%–36% yield. The coupling of 2-aryloxazolines with internal alkynes affords polycyclic oxazoliniums with up to 81% yield by Rh-catalyzed C.H bond functionalization. X-ray crystallographic analysis and circular dichroism reveal the successful coupling of chiral (R)-2-aryloxazolines with internal alkynes and affording the corresponding chiral (R)-oxazoliniums. Cytotoxicity analysis of the polycyclic oxazolinium compounds reveals cytotoxic activity on cancerous HeLa cells in micromolar dosage, with the lowest IC₅₀ of 6.4 μM.