Özden Özel Güven

Synthesis of di- and cis-triaryl-3a,4,5,6-tetrahydroimidazo[1,5-b]isoxazoles and their ring-opening reactions

Abstract The Δ3-imidazoline 3-oxides 1 undergo diastereoselective cycloaddition with dimethyl acetylenedicarboxylate 2 to give 3a,4,5,6-tetrahydroimidazo[1,5-b]isoxazoles 3. Thermally and base induced ring-opening reactions of compounds 3 were demonstrated. cis-6-Phenyl substituted adducts 3d,e undergo ring opening with secondary but not with tertiary amines. The same adducts undergo regio- and diastereoselective Michael addition with sodium methoxide to give 2-methoxy-3a,5,6-triphenyl-hexahydro-imidazo[1,5-b]isoxazole-2,3-dicarboxylic acid dimethyl esters 6.

The first examples of di- and cis triaryl-3a,4,5,6-tetrahydroimidazo[1,5-b]isoxazoles and their ring-opening reactions

Abstract The Δ 3 -imidazoline 3-oxides 1 undergo diastereoselective cycloaddition with dimethyl acetylenedicarboxylate 2 to give 3a,4,5,6-tetrahydroimidazo[1,5- b ]isoxazoles 3 . Thermal and base induced ring-opening reactions of compounds 3 were demonstrated.

The first regio- and diastereoselective synthesis of homochiral perhydroimidazoisoxazoles via the 1,3-dipolar cycloaddition of imidazoline 3-oxides with (1S)-(−)-β-pinene

Abstract The 1,3-dipolar cycloaddition of imidazoline 3-oxides 1 with (1 S )-(−)-β-pinene proceeds regio- and diastereoselectively to give homochiral perhydroimidazoisoxazole derivatives 3 in high yields in the cases of imidazoline 3-oxides 1a – e but in low yields in the reactions of 1f – g . The preferred attack of (1 S )-(−)-β-pinene to the cyclic nitrone was shown to be anti–endo. The reaction of racemic nitrones (±)- 1f – g with the homochiral β-pinene gave the adduct from the ( S )-nitrone and the corresponding imidazole. The adducts 3 undergo retro-1,3-dipolar cycloaddition when heated in the condensed phase or in diphenyl ether to give the corresponding imidazole and β-pinene.

1-[2-(2,6-Dichloro­benz­yloxy)-2-(2-fur­yl)eth­yl]-1H-benzimidazole

In the molecule of the title compound, C20H16Cl2N2O2, the planar benzimidazole ring system is oriented with respect to the furan and dichlorobenzene rings at dihedral angles of 53.39 (6) and 31.04 (5)°, respectively. In the crystal structure, intermolecular C—H⋯Cl hydrogen bonds link the molecules into centrosymmetric R 2 2(8) dimers. These dimers are connected via a C—H⋯π contact between the benzimidazole and the furan rings, and π–π contacts between the benzimidazole and dichlorobenzene ring systems [centroid–centroid distances = 3.505 (1), 3.567 (1), 3.505 (1) and 3.567 (1) Å].

1-[2-(4-Fluoro­benz­yloxy)-2-phenyl­ethyl]-1H-benzimidazole

The asymmetric unit of the title compound, C22H19FN2O, contains two independent molecules. The planar benzimidazole ring systems are oriented with respect to the phenyl/fluorobenzene rings at dihedral angles of 31.10 (4)/45.17 (5) and 45.52 (5)/68.63 (5)°, respectively, for the two molecules. In the crystal structure, intermolecular C—H⋯N and intermolecular C—H⋯N and C—H⋯F hydrogen bonds link the molecules into a three-dimensional network. There are C—H⋯π contacts between the benzimidazole and fluorobenzene rings and a π–π contact between the benzimidazole and phenyl ring systems [centroid–centroid distance = 4.575 (1) Å].

1-[2-(3,4-Dichloro-benz-yloxy)-2-phenyl-ethyl]-1H-benzimidazole.

In the molecule of the title compound, C22H18Cl2N2O, the planar benzimidazole ring system is oriented with respect to the phenyl and dichlorobenzene rings at dihedral angles of 12.73 (3) and 36.57 (4)°, respectively. The dihedral angle between the dichlorobenzene and phenyl rings is 29.95 (6)°. There are C—H⋯π contacts between the benzimidazole and dichlorobenzene rings, between the benzimidazole and phenyl rings, and between a methylene group and the dichlorobenzene ring.

1-{2-Phenyl-2-[4-(trifluoro­meth­yl)­benzyl­oxy]eth­yl}-1H-benzimidazole

The asymmetric unit of the crystal structure of the title compound, C23H19F3N2O, contains two independent molecules. In the two molecules the planar benzimidazole ring systems are oriented with respect to the phenyl/trifluoromethylbenzene rings at dihedral angles of 9.62 (6)/78.63 (7) and 2.53 (8)/83.83 (9)°. In the crystal structure, intermolecular C—H⋯N hydrogen bonds link the molecules into R 2 2(6) dimers. The molecules are elongated along [001] and stacked along the b axis.

1-[2-(4-Chloro­benz­yloxy)-2-phenyl­ethyl]-1H-benzotriazole

The asymmetric unit of the title compound, C21H18ClN3O, contains two crystallographically independent molecules which differ slightly in the orientations of chlorobenzyloxy units. In one of the molecules, the phenyl and chlorophenyl rings are oriented at dihedral angles of 38.09 (6) and 42.15 (6)°, respectively, with respect to the benzotriazole ring [43.23 (6) and 29.80 (6)° in the other molecule]. The dihedral angle between the phenyl and chlorophenyl rings is 77.63 (6)° in one of the molecules and 72.97 (6)° in the other. The crystal structure is stabilized by weak C—H⋯π interactions.

2-(1H-Benzotriazol-1-yl)-1-phenyl­ethanol

In the title compound, C14H13N3O, the benzotriazole ring is oriented at a dihedral angle of 13.43 (4)° with respect to the phenyl ring. In the crystal structure, intermolecular O—H⋯N hydrogen bonds link the molecules into chains along the b axis. Aromatic π–π contacts between benzene rings and between triazole and benzene rings [centroid–centroid distances = 3.8133 (8) and 3.7810 (8) Å, respectively], as well as a weak C—H⋯π interaction involving the phenyl ring, are also observed.

2-(2H-Indazol-2-yl)-1-phenyl-ethanone.

The asymmetric unit of the title compound, C15H12N2O, contains two independent molecules with different conformations, the phenyl ring and indazole mean plane in the two molecules forming dihedral angles of 50.82 (5) and 89.29 (6)°. In the crystal, weak C—H⋯O and C–H⋯N hydrogen bonds and C—H⋯π interactions consolidate the packing.