Construction of spiropyrans via [4+2] photocycloaddition reactions and its computational investigation

Abstract

Abstract

[4+2]-Photochemical cycloaddition provides one of the most efficient and versatile route for the exploring of carbocyclic and heterocyclic frameworks of different sizes with high atom economy. [4+2] photocycloaddition of the chalcones (2a-h) obtained by Knoevenagel condensation of thiosatin and different heteroaryl ketones viz. 2-acetyl, 3-acetyl, 4-acetylpyridines and 2-acetylthiophene olefinic 2-chloropropene with as dienophiles led to the construction of six membered novel spiropyran heterocycles (3a-h) with 60% yield. The mechanism of the [4+2] photocycloaddition reaction has been investigated in detail by DFT-B3LYP/6-31-G+ (2d, 2p) computational method.