DDQ promoted the reaction of 3-(indol-3-yl)-1,3-diphenylpropan-1-ones with 3-methyleneoxindoles in refluxing ethanol resulting in functionalized dihydrospiro[carbazole-1,3′-indolines] in good yields and with high diastereoselectivity. Similar reactions with 5-arylidene-1,3-dimethylbarbituric acids also afforded functionalized spiro[carbazole-1,5′-pyrimidines] in satisfactory yields. The reaction actually proceeded via the DDQ oxidative dehydrogenation of 3-(indol-3-yl)-1,3-diphenylpropan-1-ones to the corresponding 3-vinylindoles, their sequential Diels–Alder reaction with dienophiles and further isomerization process. DFT calculations showed that the Diels–Alder reaction has a normal electron-demanding character.