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Zusammenfassung:
The photochemical properties of the title compounds have been investigated and compared. The benzoxazino-benzoxazine derivatives 1 are photochemically converted into hydrogenated oxazole derivatives. In some cases this ring contraction is accompanied by a dehydrogenation reaction whereby the heterocyclic ring system becomes aromatic. Hydrogenated quinoxalino-quinoxalines also undergo a photodehydrogenation reaction and become aromatic. However, a ring contraction yielding the imidazolyl system does not take place. The only investigated sulfur-containing analog has different properties. The stable form is the bibenzothiazole 23 which contains a five-membered heterocyclic ring system. Photochemically 23 rearranges under ring expansion to give the benzothiazino-benzothiazine 24.
