Regioselective construction of diverse and multifunctionalized 2-hydroxybenzophenones for sun protection by indium(iii)-catalyzed benzannulation†
Diverse and functionalized 2-hydroxybenzophenone derivatives were synthesized efficiently in good to excellent yield via the highly regioselective indium(III)-catalyzed [2+2+2] benzannulation of 3-formylchromones with β-enamino esters or β-enamino ketones. This benzannulation reaction proceeds via a domino Michael/retro-Michael/6π-electrocyclization/deformylation reaction. In addition, 2-hydroxybenzophenones were also prepared by the indium(III)-catalyzed [4+2] benzannulation reaction between 3-substituted chromen-4-ones and β-enamino esters or β-enamino ketones. Furthermore, the effects of substituents and π conjugation on the characteristics of the UV-Vis spectrum of synthesized 2-hydroxybenzophenones were examined. Compound 10s exhibited higher sun protection activity than oxybenzone which is used in most popular sunscreens.