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

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 H-1 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 x 10(4) and 4.9 x 10(4) dm(3) mol(-1) cm(-1), respectively, for 5a and b.