The acyl radical was trapped by radical scavengers like TEMPO and DPE, indicating involvement of radical in the mechanism (Figure ). O labelling studies that revealed a substantial 23.3% O incorporation in the product (after debenzoylation, cyclization, and dehydration under gas chromatography-mass spectrometry conditions) were indicative of the migration taking place through the contact ion pair (CIP) method (Figure ). The cross-over experiment exclusively yielded non-crossover products suggesting a concerted or an in-cage, stepwise pathway for the acyloxy migration (Figure ). These preliminary mechanistic investigations proposed the following mechanism (Figure ); the photoexcited [Cu(I)] complex (16.21) is oxidatively quenched by acyl chloride, yielding acyl and Cl radicals alongside [Cu(II)Cl] complex (16.22). Subsequently, 16.22 undergoes LMCT to liberate Cl radical thus regenerating [Cu(I)] (16.20) and completing the catalytic cycle. Both Cl and acyl radicals react with THF solvent giving ride to THF adducts. The radical cross-coupling of acyl radical, with the triplet (T1) nitro(hetero)arene forms an unstable intermediate, 16.25, that collapses to release a carboxylate radical and nitrosoarene (16.27). The nitrosoarene further traps second and third acyl radicals, yielding the bis-acylated hydroxylamine intermediate, 16.29. The subsequent intramolecular acyloxy migration followed by tautomerization forms the desired product (16.32).