First permanent opened forms in spiro[indoline-oxazine] series: synthesis and structural elucidation

Abstract

The geometrical structure (TTC isomer), as well as the electronic distribution (quinoidic form), of the first permanent opened forms of spirooxazines 5a and b have been determined by ¹H NMR spectroscopy and dipole moment measurements. The crystal structure of compound 5b has been determined by X-ray diffraction to confirm the conformations. Molar absorption coefficients were found to be 4.8 × 10⁴ and 4.9 × 10⁴ dm³ mol^–1 cm^–1, respectively, for 5a and b.