[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.

中文翻译：

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通过[4 + 2]光环加成反应构建螺吡喃及其计算研究

[4 + 2]-光化学环加成法是探索具有高原子经济性的不同大小的碳环和杂环骨架的最有效和通用途径之一。[4 + 2]通过硫代缎和不同杂芳基酮的Knoevenagel缩合获得的查耳酮（2a-h）的光环加成。与作为亲二烯体的2-乙酰基，3-乙酰基，4-乙酰基吡啶和2-乙酰基噻吩烯属的2-氯丙烯导致了六元新型螺吡喃杂环（3a-h）的构建，产率为60％。已通过DFT-B3LYP / 6-31-G +（2d，2p）计算方法详细研究了[4 + 2]光环加成反应的机理。