Synthesis of Dioxapropellanes Using Mn(III)-Based Oxidative Tandem Cyclization of Tetracarbonyl Compounds with Diarylethenes

Abstract

The Mn(III)-based oxidation of tetracarbonyl compounds with 1,1-diarylethenes formed dioxapropellanes. The use of methylenebis(3-hydroxycyclohex-2-en-1-one)s as a tetracarbonyl compound led to the production of 3,4,5,6,7,9-hexahydro-8H-4a,9a-(epoxyethano)xanthene-1,8(2H)-diones in good yields. Although the reaction competed with the self-cyclization to form 3,5,6,7-tetrahydro-4H-spiro[benzofuran-2,1'-cyclohexane]-2’,4,6'-triones, it could be controlled by adding the co-solvent formic acid at room temperature. The reactions of alkyl- and aryl-substituted methylenebis(3-hydroxycyclohex-2-en-1-one)s resulted in the corresponding dioxapropellanes as a diastereomixture. The formation of the diastereomers was explained by the steric hindrance of the intermediate carbocations during the tandem cyclization. The reactions using 2-(2-hydroxy-4,4-dimethyl-6-oxocyclohex-1-en-1-yl)butane-1,4-diones and 2,2'-methylenebis(3-hydroxycyclopent-2-en-1-one)s also produced the corresponding dioxapropellanes. The structure determination of the products and the reaction pathway for the formation of the dioxapropellanes are discussed.