Acyl radicals, characterized by their sp 2 -hybridized nature, demonstrate a distinctive reactivity owing to the electron-donating lone pair of the carbonyl oxygen. This hyper-conjugation raises the energy level of the singly occupied molecular orbital (SOMO), rendering acyl radicals nucleophilic in nature-an attribute commonly referred to as umpolung phenomena in organic chemistry. Whilst various homo-and heteroleptic Cu(I) complexes have been employed for C-Br and C-I bond activation, Ngai and co-workers in 2022, harnessed the versatile reactivity of Cu(I) photocatalysts to activate more challenging C-Cl bonds in acyl chlorides showcasing their utility as effective acyl radical precursors (Figure ). Employing a unique Cu(I)-NHC complex in conjunction with BINAP, the authors established a tandem acyl radical addition-cyclization strategy enabling the modular synthesis of more than 10 distinct classes of heterocycles. Moreover, this methodology was extended as a protocol for late-stage functionalization of bio-relevant scaffolds such as derivatives from leucine, efavirenz, and thiabendazole (Figure ). 116 Mechanistic investigations such as time-dependent mass spectrometric analysis unveiled an interplay of synergistic excited-state copper catalysis involving [Cu(IPr)2] + (13.5) and in-situ generated [Cu(BINAP)2] + (13.4) complexes. Notably, the luminescence emission of the latter was quenched by the acyl chloride, indicating the formation of acyl radicals via oxidative quenching of the excited state [Cu(BINAP)2] + (13.7) (Figure ). The acyl radical subsequently engages in radical 6-exo-trig cyclization upon addition onto the olefin, followed by ligand exchange or carbocupration with [Cu(IPr)2] + to form 13.13. Oxidation of 13.13 to Cu(III) complex (13.14) by 13.9 followed by C-Cl reductive elimination and condensation furnishes the desired heterocyclic product 13.15, and regenerates [Cu(IPr)2] + (13.16) upon re-coordination of IPr ligand, completing [Cu(IPr)2] + catalytic cycle.