Oxidative behaviour of 3-aryl-2H-1,4-benzoxazines

Autoxidation of 3 - phenyl - 2H - 1,4-benzoxazine 8 gives 2 - hydroxy -3 - phenyl - 2H - 1,4-benzoxazine 13, 3 - phenyl - 2H - 1,4-benzoxazin - 2 - one 11, and 2 - phenylbenzoxazole 10 according to the conditions. Oxidation of 8 with DDQ in the presence of air gave mainly the bisacetal 17 but in the absence of air the major product was trans-Δ^2,2′-bi-(3-phenyl-2H-1,4-benzoxazine) 21a. Corresponding dimers were obtained from the 3-p-bromophenylbenzoxazine 9. The trans-isomers 21a and 22a are photochromic and change into their cis-isomers on exposure in solution to direct sunlight.