Synthesis of Polycyclic Oxazolinium Compounds from Aryloxazolines and Alkynes <i>via</i> 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 IC 50 of 6.4 μM.