Green synthesis of 1,3-oxazines by visible light-promoted catalyst-free C–H activation/cyclization of tertiary amines.

Saikia, B. Shriya; Deb, Mohit L.; Baruah, Pranjal K.

To achieve the goal of green chemistry and sustainable development, catalyst-free reactions and use of naturally abundant resources are gaining importance. In last two decades, C–H functionalization has gained attention for the synthesis of organic molecules. Here, we report a catalyst-free cross-dehydrogenative coupling reaction promoted by visible light for the synthesis of 1,3-oxazines. When α-aminoalkylnaphthols/phenols, commonly known as Betti bases, are irradiated with white light-emitting diode (LED, 23 W) in dimethyl sulfoxide (DMSO) solvent in an open reaction vessel at room temperature, cyclization takes place via α-C–H activation of tertiary amine moiety and forms a new C–O bond. Biologically important 1,3-oxazines are obtained in 58–85% yields. The various advantages of this methodology are (i) the reaction is catalyst-free, (ii) only aerial oxygen is needed as the oxidant, (iii) the reaction is visible light-promoted and (iv) a broad range of 1,3-oxazines are synthesized by varying the tertiary amine moiety or naphthols/phenols or the aryl substituent of the substrate Betti bases.

OXAZINES; TERTIARY amines; RING formation (Chemistry); CATALYSTS; DIMETHYL sulfoxide; VISIBLE spectra; SUSTAINABLE chemistry; LIGHT emitting diodes

Environmental Chemistry Letters, 2022, Vol 20, Issue 1, p109

1610-3653

Academic Journal

10.1007/s10311-021-01308-6