No abstract

The 1,3-dipolar cycloaddition of cyanonitrile oxide to 2,3- and 2,5-dihydrofurane, 7-oxabicyclo[2,2,1]-2-heptene and derivatives of 1,3-dioxep-5-ene is described. The condensed isoxazolines Ia, IIIa, Va, Vc, Vd thus prepared are rearranged on irradiation into cyanosubstituted heterocyclic enaminoaldehydes IIa, IVa, VIa, VIc. The quantum yields of the photorearrangement of cyanoderivatives are higher than those of the phenyl derivatives, being within the limits from 0·068 to 0·19. The reaction of II with hydrazine gives the derivative IX of oxazino[4,5-d]pyridazine.

2-Chloro-1,3-dithiane was obtained by the chlorination of 1,3-dithiane with N-chlorosuccinimide. Reactions of 2-chloro-1,3-dithiane with various substituted phenols lead to 2-(1,3-dithianyl)phenols (3). Hexakis-[p-(1,3-dithian-2-yl)phenoxy]cyclotriphosphazene (6) was obtained by reaction with hexachlorotriazacyclotriphosphazene (5).

Preparation and photolysis of furoisoxazoline derivatives is described. The respective compounds IVa, II and VI were obtained by a 1,3-dipolar cycloaddition of benzenenitrile oxide to 5,6-dimethoxycarbonyl-7-oxabicyclo[2,2,1]-2-heptene, 2,5-dihydrofuran and furan; IVb was synthesized from benzoylnitrile oxide. The biradical primarily formed by photolysis was stabilized with respect to the arrangement of the heteroatom and the isoxazoline chromophore. The new 1,3-oxazine derivatives III and V were obtained in high yields as single products. The quantum yield of photoreaction of II, IVa and XXVII was found to be 0.04, 0.26 and 0.07, respectively. Were the stabilization of the radical by conjugation with the lone electron pair of oxygen impossible, oxazoline VII should be formed. Photolysis of the benzoyl derivative IVb had an anomalous course and yielded the β-aminochalcone Xb.

Photochemical reactions of 2-substituted furans I, IV and V with benzaldehyde, benzophenone and 4-methylbenzophenone gave substitued 2,7-dioxabicyclo[3,2,0]-3-heptenes, which can be used for syntheses of 2,3- or 2,4-disubstituted furans. Regioisomeric (2:1)-cycloadducts XV and XVI were distinguished on the basis of their 1H and 13C NMR spectra.