Regioselectivity observed in manganese(III) acetate mediated addition of acetylacetone to various alkenes: mechanistic and theoretical studies

Abstract

Various alkenes substituted at the 1,2-positions by 2-thiophenyl, 3-thiophenyl, and phenyl substituted by electron-withdrawing and electron-donating groups were treated with acetylacetone in the presence of Mn(OAc)3 in acetic acid. In cases where the thiophene ring was connected at the C-2 carbon atom to the double bond, a single regioisomer was formed whereas in case of substitution at the C-3 positions two regioisomers were formed. Stilbene derivatives also gave two regioisomers under the same reaction conditions. However, 1-methoxy-4-(4-nitrostyryl)benzene provided a single cycloaddition product. The observed regioselectivity was discussed in terms of atomic charge distribution on the olefinic double bond carbon atoms. Furthermore, activation barriers for transition states were calculated.