Halogen Bond Assisted Light Responsiveness of <i>Para</i>‐Quinone Methides for 1,6‐Conjugate Addition Reactions

Abstract The ability to change the essential characteristics of the molecular systems using light is highly promising and finds use in photocatalysis and materials chemistry. A critical requirement for such systems is that molecules should directly absorb light in the visible region. Though small molecule activation by visible light is challenging, they on complexation with certain species respond to visible light favourably. Herein, we disclose the catalytic application of CBr 4 as a halogen bond donor catalyst to activate para ‐quinone methides towards visible light photo‐catalysed reactions. This protocol facilitates 1,6‐conjugate addition reactions with various nucleophiles, forming C−C and C−O bonds in para ‐quinone methides, yielding the desired products in good to excellent yields. Mechanistic investigations reveal that para‐ quinone methide responds to visible light only when complexed with CBr 4 . The synthetic utility of this protocol is demonstrated through the one‐pot synthesis of spiro‐cyclohexadienone compounds from 2‐naphthol and para ‐quinone methide.