Cross-Coupling of Amide and Amide Derivatives to Umbelliferone Nonaflates: Synthesis of Coumarin Derivatives and Fluorescent Materials

The
Buchwald–Hartwig cross-coupling reaction between 4-methylumbelliferone-derived
nonaflates with amides, carbamates, and sulfonamides is described.
A wide variety of N-substituted 7-amino coumarin
analogues was prepared in good to excellent yields. The photophysical
properties of aqueous-soluble derivatives were determined, and they
displayed auxochrome-based variations. Gram-scale synthesis provided
an acrylamide analogue, which was used to fabricate a fluorescent
poly­(2-hydroxylethyl methacrylate) (pHEMA) hydrogel that was resistant
to leaching in ultrapure H2O. We envisage that our reported
protocol to access 7-amino-4-methylcoumarin derivatives will find
use toward the development of new fluorescent coumarin-based probes
by researchers in the field.