Synthesis and Photophysical Properties of 1,4-Dihydro-2 H,5H-chromeno[4,3-D][1,3]oxazin-5-ones, and Derivatives Containing Tethered 1,2,3-Triazoles, from 4-Aminocoumarins

Abstract

A facile protocol for the unprecedented one-pot H 2 SO 4 -mediated hydroxymethylation/cyclative N, O -acetalization of 4-aminocoumarins to 1,4-dihydro-2 H,5 H -chromeno[4,3- d ][1,3]oxazin-5-ones, in moderate to good yields, was developed and optimized. The scope and limitations of the transformation, which takes place in water or water/THF mixtures, were also studied. The nitrogen atom of the resulting tricycles was used to tether alkyl, aryl and 1,2,3-triazolylmethyl moieties, employing a two-step click chemistry approach for the latter. The photophysical properties of the heterocycles, as well as of their 1,2,3-triazole derivatives, were also examined. The N -aryl derivatives exhibited high quantum yields of fluorescence (up to Φ f = 0.69) and very large Stokes shifts (up to 201 nm).