The purple pigments produced by acetylation of 2-(2-oxoindolin-3-yl)-glyoxylates in the presence of pyridine
Abstract
The reaction of 2-(2-oxoindolin-3-yl)glyoxylates with acetic anhydride in the presence of pyridine gives insoluble purple pigments in which two molecules of the indoline have condensed with one molecule of acetic anhydride and for which a spirocyclobutene structure (13a) is suggested. The mode of formation of the pigments is discussed.