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A synthesis of the carbopyronine dye Carboxy ATTO 647N from simple materials is reported. This route proceeds in 11 forward steps from 3-bromoaniline with the key xanthone intermediate formed using a new oxidation methodology. The step utilizes an oxidation cycle with base, water, iodine, and more than doubles the yield of the standard permanganate oxidation methodology, accessing gram-scale quantities of this late-stage product. From this, Carboxy ATTO 647N was prepared in only four additional steps. This facile route to a complex fluorophore is expected to enable further studies in fluorescence imaging.

A base-catalyzed direct oxidation of rhodamine, carborhodamine, and siliconrhodamine pyronines to the corresponding xanthones is studied. This methodology utilizes addition of water to split pyronines into xanthone and reduced xanthene, the latter of which is returned to pyronine by oxidation with iodine. The transformation is general, working on the three most recalcitrant versions of N, N, N', N'-tetramethylpyronines in good to excellent yields.