The indium(iii) chloride catalyzed synthesis of sulfur incorporated 3-acylcoumarins; their photochromic and acetate sensing properties

Abstract

The synthesis and evaluation of the photochromic properties of 3-acylcoumarins are very important as they exhibit selective sensing properties. We found that InCl₃ efficiently catalyzes the condensation of 2-hydroxybenzaldehydes and β-keto esters to provide near quantitative yields of 3-acylcoumarins. The 3-(phenylsulfanyl/phenylsulfinyl/phenylsufonyl)propanoyl coumarins with an electron-donating NMe₂ group at the C7 position were prepared to evaluate the influence of sulfur on the emission and acetate ion sensing properties. Our studies revealed that 7-(diethylamino)-3-(3-(phenylsulfanyl/phenylsulfinyl/phenylsufonyl)propanoyl)-2H-chromen-2-one exhibits excellent fluorescence emission in hexane and ethyl acetate (Φ ≈ 80%). The 3-acylcoumarin with sulfone in the C3-acyl side-chain detects acetate anions selectively and this property can be conveniently followed by fluorescence emission spectroscopy.