5-SPIROCYCLOALKANE ISOXAZOLINES - STRUCTURES AND THERMAL-BEHAVIOR

(1): 3-Phenyl-4,5-dihydroisoxazole-5-spirocyclopropane, C11H11NO, M(r) = 173.21, monoclinic, P2(1)/n, a = 10.052 (4), b = 5.732 (8), c = 16.091 (10) angstrom, beta = 99.41 (4)-degrees, V = 915 (1) angstrom 3, Z = 4, D(x) = 1.26 g cm-3, mu = 0.76 cm-1, F(000) = 368, T = 298 K, final R = 0.094 for 407 observed reflections [I > 3-sigma(I)]. (2): 3-Phenyl-4,5-dihydroisoxazole-5-spirocyclobutane, C12H13NO, M(r) = 187.24, orthorhombic, P2(1)2(1)2(1), a = 5.845 (2), b = 8.887 (2), c = 19.236 (5) angstrom, V = 999.2 (5) angstrom 3, Z = 4, D(x) = 1.24 g cm-3, mu = 0.74 cm-1, F(000) = 400, T = 298 K, final R = 0.066 for 679 observed reflections [I > 3-sigma(I)]. (3): 3-Phenyl-4,5-dihydroisoxazole-5-spirocyclopentane, C13H15NO, M(r) = 201.27, orthorhombic, P2(1)2(1)2(1), a = 8.057 (10), b = 11.169 (5), c = 12.251 (9) angstrom, V = 1102 (2) angstrom 3, Z = 4, D(x) = 1.21 g cm-3, mu = 0.71 cm-1, F(000) = 432, T = 298 K, final R = 0.075 for 502 observed reflections [I > 3-sigma(I)]. 5-Spirocyclopropane and 5-spirocyclobutane isoxazolines undergo thermal rearrangement to give mainly 2-phenyl-5,6-dihydropyrid-4-one and 2-phenyl-5,6,7,8-tetrahydro-4H-azepin-4-one respectively under rather different experimental conditions. Geometrical parameters of the 5-spirocyclopropane and 5-spirocyclobutane isoxazolines, derived from the X-ray analysis, were used to justify the origin of their different thermal behaviour.