Diastereoselective (8+3)‐Cycloadditions of Donor‐Acceptor Cyclopropanes with Tropothione

Abstract Reactions of dimethyl 2‐arylcyclopropane‐1,1‐dicarboxylates, used as representatives of D‐A cyclopropanes, with tropothione were carried out in the presence of scandium triflate as a catalyst, under mild conditions (CH 2 Cl 2 solution, rt). The anticipated (8+3)‐cycloaddition products, cycloheptatriene fused thiopyrans, were obtained in good to excellent yields. Cycloadditions occurred with complete diastereoselectivity and in all cases single diastereomers were formed. Structures of isolated cycloadducts were established based on spectroscopic data and in two cases they were unambiguously confirmed by single crystal X‐ray diffraction analysis. In contrast to an analogous (8+3)‐cycloaddition reported for parent tropone, which was performed in the presence of Ni(ClO 4 ) 2 , no 1,3‐ H shift leading to products possessing a CH 2 moiety located within the seven‐membered ring was observed.