Reaction of pyrroles with naphthoquinones. Synthesis of new pyrrolylnaphthoquinone dyes

The reaction of 1,4-naphthoquinone (1) with N-alkylpyrroles (2) gives a mixture of 2-(pyrrol-2-yl)-1,4-naphthoquinones (3) and 2,5-bis(1,4-naphthoquinon-2-yl)pyrroles (4). The yields and the ratios of these two products depend greatly on the experimental conditions. The reaction has been extended to 5-hydroxy-1,4-naphthoquinone (juglone, 5) and 1,2-naphthoquinone (6). New pyrrolylnaphthoquinones are obtained.