Polycyclic hydroxyquinones. Part 26. Regio- and site-selectivity in the Diels–Alder reactions of 4-sulphonyliminoanthracene-1,9,10-triones

Abstract

The lead tetra-acetate oxidation of anthraquinones (9)–(11) afforded the corresponding anthracenediquinone monosulphonylimines (14)–(16) in good yields. The diquinone imine (14) reacted with 2,3-dimethylbuta-1,3-diene (17) to furnish mainly the linear Diels–Alder adduct (23) whereas with electron-rich dienes, such as (E)-1-methoxybuta-1,3-diene (18), a mixture of the linear adduct (24) and the bridged adduct (29) was obtained. The latter reaction is regiospecific and the regiochemistry is controlled by the sulphonylimino group. The cycloaddition of chlorodiquinone imine (16) with dienes (18), (20), and cyclopentadiene occurred only at the internal 4a,9a-double bond to afford bridged adducts. The cycloaddition of (14) with less electronrich dienes, such as 2-acetoxybuta-1,3-diene (21) and (E)-3-acetoxy-1-trimethylsilylbuta-1,3-diene (22), gave only the linear adducts (26a,b) and (27), respectively. The latter, which is obtained as a sole regioisomer, is a precursor of anthracyclinones.