Bromination of photochromic spironaphthoxazines

Direct bromination of photochromic compounds of the spironaphthoxazine and spironaphthopyran series was performed using N-bromosuccinimide to obtain both photochromic bromine-substituted spiro compounds and nonphotochromic 2-(naphtho[1,2-d]oxazol-2-yl)-3H-indolium bromides. The structures of the resulting products were established by NMR spectroscopy and mass spectrometry. The mechanism of bromination taking into account the involvement of both closed and open (colored) forms of spiro compounds was proposed.