A series of 6,7-disubstituted 2-hydroxy-3-nitronaphthazarins were prepared by treatment of 2,3-dichloronaphthazarins with sodium nitrite. Acid-catalyzed hydrolysis of a mixture of two isomeric 6(7)-ethoxy-7(6)-ethyl-substituted 2-hydroxy-3-nitronaphthazarins followed by chromatographic separation led to the individually precursors of echinamines A and B. Further reduction of nitroquinones using various reducing agents gave echinamines and related 3-amino-2-hydroxynaphthazarins in good yields.
DMSO-mediated transformation of 3-amino-2-hydroxynaphthazarins to natural 2,3-dihydroxynaphthazarins and related compounds
作者:Nikita S. Polonik、Sergey G. Polonik
DOI:10.1016/j.tetlet.2016.06.056
日期:2016.7
A general and convenient method for the synthesis of naturallyoccurring and related hydroxylated naphthazarins has been developed. This protocol involves the oxidative DMSO-mediated transformation of 3-amino-2-hydroxynaphthazarins to 2,3-dihydroxynaphthazarins under acidic conditions. Based upon experimental observations, a plausible reaction mechanism is proposed.