Synthesis and Photophysical Properties of 1,4-Dihydro-2H,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 H2SO4-mediated hydroxymethylation/cyclative N,O-acetalization of 4-aminocoumarins to 1,4-dihydro-2H,5H-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 Φf = 0.69) and very large Stokes shifts (up to 201 nm).

Synthesis, characterization and photophysical studies of dual-emissive base-modified fluorescent nucleosides

“…23,24 Dihydro-oxazines are known for their compact nature, improving the Stokes shift values, which have made them promising candidates for application as fluorescent probes. 25 To overcome these drawbacks and enhance the utility of the coumarin scaffold as a fluorescent probe with larger Stokes shift values, we have coupled dihydro [1,3]oxazine with coumarin derivatives. Furthermore, most environment-sensitive fluorescent nucleosides exhibit single-band emission and often lack microenvironment sensitivity and have low quantum yields.…”