Regioselective construction of diverse and multifunctionalized 2-hydroxybenzophenones for sun protection by indium(iii)-catalyzed benzannulation

Abstract

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.

Base‐Promoted Direct Cascade Transformation of Chromones to Coumarins via Benzannulation and Transesterification

“…However, polar solvents such as acetonitrile and ethanol failed to afford the desired product (entries 8-11). Using toluene as a solvent, when the reaction temperature was decreased to room temperature, 50 °C or 80 °C, 3 a was isolated in a trace amount, 20% or 55% yield, respectively (entries [12][13][14]. The 1 H NMR spectrum of 3 a exhibits three methyl singlet peaks corresponding to the methoxy, acetyl, and methyl groups at δ 3.86, 2.82, and 2.37 ppm, respectively.…”

“…[13] Our group has previously developed an In(III)catalyzed reaction of 3-substituted chromen-4-ones and βenamino esters used for the construction of 2hydroxybenzophenones. [14] In this case, coumarin products were not formed. As an on-going study toward the annulation reactions using 3-substituted chromen-4-ones, [15] we herein report a mild base-promoted reaction of 3-substituted chromones and β-keto esters used for the synthesis of 3-acyl-4arylcoumarins via cascade benzannulation and transesterification processes (Scheme 1d).…”

“…Recently, benzannulation reaction has become a versatile platform for the construction of diverse aromatics from acyclic precursors [13] . Our group has previously developed an In(III)‐catalyzed reaction of 3‐substituted chromen‐4‐ones and β ‐enamino esters used for the construction of 2‐hydroxybenzophenones [14] . In this case, coumarin products were not formed.…”

Multicomponent Cascade Reaction of 3-Formylchromones: Highly Selective Synthesis of Functionalized 9-Azabicyclo[3.3.1]nonane Derivatives

“…The 3-formylchromones and their analogs are diverse building blocks − used in the preparation of heterocycles. To further investigate the multicomponent reaction of 3-formylchromones, we used two different types of dinucleophiles, namely enaminones and HKAs, to study this model reaction promoted by different bases.…”

Synthesis and Reactivity of Electron-Deficient 3-Vinylchromones

“…Scheme 45 Reaction of chromones 2 with 1,3-dicarbonyl compounds 2-Hydroxybenzophenones 111, with a different set of substituents, were obtained from chromones 2 and -enaminoesters or -enaminoketones by the [4+2] benzannulation reaction, catalyzed by indium(III) triflate in acetonitrile at room temperature (Scheme 46). 68 In this transformation, the role of 1,2-ambiphile was performed by ketoenamines.…”