CuOTf/TfOH-mediated tandem reaction of conjugated ene-yne-ketones: Synthesis of novel spiro dihydrofurans

Abstract CuOTf/TfOH-mediated cascade cyclization-coupling-electrophilic substitution of conjugated ene-yne-ketones in DCE at 25 °C provided novel spiro dihydrofurans in 32–83% yield. The experimental results demonstrated that substituent group R3, which is electron-donated or electron-withdrawing group, decreased the yield. Additionally, significant effects of R2 group adjacent to carbonyl carbon on reactivity and yield of the reaction were also observed. Both the reactivity and yield were decreased when replacing methyl group or ethyl group with bulky substituent group (e.g., aryl group, cyclopropyl group). For 3-(3-cyclopropylprop-2-yn-1-ylidene)pentane-2,4-dione, tetrahydro-6H-furo[2′,3’:1,5]cyclopenta[1,2-b]pyran was generated. This method proved to be simple and mild.