Collect. Czech. Chem. Commun. 1988, 53, 3171-3178

An unusually selective photo-induced rearrangement of 4-alkoxycarbonyl-5-formyl-2,3-dihydro-6H-1,3-oxazines. A new route to preparation of condensed lactones

Vladimír Oremusa, Lubor Fišeraa, Hans-Joachim Timpeb and Ute Lammelb

a Department of Organic Chemistry, Slovak Institute of Technology, CS-812 37 Bratislava, Czechoslovakia
b Department of Photochemistry, Technical University, DDR-4200 Merseburg, G.D.R.


3-R-Alkoxycarbonyl-5-formyl-2,3-dihydro-6H-1,3-oxazines IIa-IIc (R = methyl, ethyl, isopropyl) as primary photoproducts formed by a rearrangement of 3-R-alkoxycarbonyl-3a,4,6,6a-tetrahydrofuro[3,4-d]isoxazoles Ia-Ic undergo cyclization to bicyclic lactones IIIa-IIIc due to further irradiation. The photochemical transformation of compounds II into III constitutes a new kind of photo-induced rearrangement. The quantum yields are very little dependent on the presence of oxygen and polarity of the solvent. The proposed concerted mechanism of the photorearrangement is discussed.