Highly regio- and diastereo-selective synthesis of novel tri- and tetra-cyclic perhydroquinoline architectures via an intramolecular [3 + 2] cycloaddition reaction.

A facile and efficient synthetic protocol was established for the construction of novel tri- and tetra-cyclic pyrrolo/pyrrolizinoquinoline architectures via the in situ formation of azomethine ylide followed by an intramolecular [3 + 2] cycloaddition reaction strategy. This protocol leads to the creation of two/three new rings and three/four contiguous stereocentres, in which one of them is a tetra-substituted carbon center, in a highly diastereoselective fashion with excellent yields.

Methyl 1-phenyl-3-p-tolyl-1,9b-di-hydro-3H-chromeno[4,3-c]isoxazole-3a(4H)-carboxyl-ate.

In the title compound, C25H23NO4, the pyran ring of the chroman moiety has an envelope conformation with the methyl-ene C atom as the flap. The isoxazole ring has a twist conformation on the O-C bond. The dihedral angle between their mean planes is 57.87 (9)°. The attached phenyl and benzene rings are twisted away from its mean plane by 56.19 (10) and 50.57 (10)°, respectively. These two rings are normal to each other, subtending a dihedral angle of 89.2 (1)°. In the crystal, there are no classical hydrogen bonds; the mol-ecules are linked via C-H⋯π inter-actions, forming a two-dimensional network lying parallel to (10-1).

Two Body Wear of Newly Introduced Nanocomposite Teeth and Cross Linked Four Layered Acrylic Teeth: a Comparitive In Vitro Study.

STATEMENT OF PROBLEM: Wear of complete denture teeth results in compromise in denture esthetics and functions. To counteract this problem, artificial teeth with increased wear resistance had been introduced in the market such as nanocomposite teeth. PURPOSE: The purpose of this study was to compare the amount of wear between nanocomposite teeth and acrylic teeth. MATERIALS AND METHODS: Fifteen specimens were chosen from each group namely the nanocomposite teeth (SR_-PHONARES) and the acrylic teeth (ACRY PLUS). Maxillary premolar was only chosen for testing and the samples were customized according to the specifications of the pin on disc machine. Pin on disc machine is a two body tribometer which quantifies the amount of wear under a specific load and time. Test samples were mounted on to the receptacle of the pin on disc machine and tested under a load of 0.3 kg for 1,000 cycles of rotation against a 600 grit emery paper. The amount of wear is displayed from the digital reading obtained from the pin on disc machine. RESULTS: After statistical analysis, it was found that, the amount of wear is more in four layered acrylic teeth. The p value obtained is 0.002 (<0.005) thus implies that the difference in wear between nanocomposite teeth and acrylic teeth is statistically significant. CONCLUSION: Though the nanocomposite teeth has less amount of wear than the four layered acrylic teeth, the difference is very less and adds only to a little clinical significance but the cost of the nanocomposite is four times that of the acrylic teeth. Further clinical studies must be performed to confirm our results.

3-(2-Methyl-phen-yl)-3a,4-dihydro-3H-chromeno[4,3-c]isoxazole-3a-carbo-nitrile.

In the title compound, C(18)H(14)N(2)O(2), the pyran ring of the chromeno ring system has a half-chair conformation, and the dihedral angle between its mean plane and the benzene ring is 5.3 (2)°. The isoxazole ring forms a dihedral angle of 74.6 (2)° with the attached benzene ring and is inclined to the mean plane of the chromeno ring system by 15.06 (19)°. In the crystal, there are no significant inter-molecular inter-actions.

Methyl 6-eth-oxy-3-phenyl-3a,4-dihydro-3H-chromeno[4,3-c]isoxazole-3a-car-boxylate.

In the title compound, C(20)H(19)NO(5), the dihedral angle between the mean plane of the pyran ring (which has a half-chair conformation) and the benzene ring of the chromeno ring system is 7.21 (7)°. The dihedral angle between the mean plane of the chromeno ring system and the isoxazole ring is 21.78 (6)°, while the isoxazole ring forms a dihedral angle of 72.60 (8)° with the attached phenyl ring. In the crystal, mol-ecules are linked via pairs of C-H⋯O hydrogen bonds, forming inversion dimers with an R(2) (2)(10) ring motif. These dimers are linked via C-H⋯N hydrogen bonds, forming chains along [001].

8-Bromo-3-phenyl-3a,4-dihydro-3H-chromeno[4,3-c]isoxazole-3a-carbo-nitrile.

In the title compound, C(17)H(11)BrN(2)O(2), the five-membered isoxazole ring has an envelope conformation with the C atom bearing the phenyl ring as the flap. The pyran ring has a half-chair conformation. In the chromeno ring system, the dihedral angle between the mean plane of the pyran ring and the benzene ring is 4.68 (2)°. The dihedral angle between the mean planes of the chromeno ring system and the isoxazole ring is 13.79 (15)°. The latter forms a dihedral angle of 34.10 (17)° with the phenyl ring. In the crystal, mol-ecules are linked by C-H⋯N hydrogen bonds, forming an undulating two-dimensional network parallel to the ab plane.

Methyl 2-[(2-chloro-quinolin-3-yl)(hy-droxy)meth-yl]acrylate.

There are two independent mol-ecules (A and B) in the asymmetric unit of the title compound, C14H12ClNO3. The mean planes of the methyl ester unit (Cmeth-yl-O-C=O; r.m.s. deviation = 0.051 Šfor mol-ecule A and 0.016 Šfor mol-ecule B) and the chloro-quilonine ring system (r.m.s. deviation = 0.023 Šfor mol-ecule A and 0.014 Šfor mol-ecule B) form dihedral angles of 63.5 (1)° in mol-ecule A and 78.1 (1)° in mol-ecule B. The main difference between the two independent mol-ecules is reflected in the (H)O-C-C=C(H2) torsion angle which is -109.7 (2)° in mol-ecule A and 10.6 (2)° in mol-ecule B. An intra-molecular O-H⋯O hydrogen bond is observed in mol-ecule A. In the crystal, mol-ecules A and B are linked into pairs via bifurcated O-H⋯(N,Cl) hydrogen bonds and a weak C-H⋯O hydrogen bond links pairs of mol-ecules into chains along [100].

rac-Methyl 3-(2-meth-oxy-phen-yl)-3a,4-di-hydro-3H-chromeno[4,3-c]isoxazole-3a-carboxyl-ate.

The title compound, C19H17NO5, comprising two stereogenic C atoms of the same configuration, crystallizes in a centrosymmetric space group as a racemate. The pyran ring adopts a half-chair conformation, while the isoxazole ring adopts an envelope conformation with the C atom bonded to the meth-oxy-phenyl group as the flap. The dihedral angle between the mean plane of the pyran ring and the adjacent benzene ring is 5.86 (5)°. In the crystal, mol-ecules are linked by a weak C-H⋯O hydrogen bond, forming a chain along the a axis.

rac-3-(4-Chloro-phen-yl)-3a,4-di-hydro-3H-chromeno[4,3-c]isoxazole-3a-carbo-nitrile.

The title compound, C17H11ClN2O2, which contains two stereogenic C atoms, crystallizes in a centrosymmetric space group as a racemate. The pyran ring and the isoxazole ring adopt sofa and twisted conformations, respectively. The dihedral angle between the benzene ring and the mean plane through the near coplanar atoms of the pyran ring is 4.17 (5)°. The mol-ecular conformation features a weak C-H⋯O contact. In the crystal, C-H⋯O hydrogen bonds link the mol-ecules, forming chains along the a-axis direction.

2-[(2-Chloro-quinolin-3-yl)(hy-droxy)meth-yl]acrylo-nitrile.

In the title compound, C13H9ClN2O, the dihedral angle between the acrylo-nitrile C=C-CN plane and the quilonine ring system is 71.3 (2)°. In the crystal, mol-ecules are linked by O-H⋯N hydrogen bonds, forming chains along [01-1]. The chains are linked into a three-dimensional network through C-H⋯N inter-actions.

8-Bromo-3-(4-ethyl-phen-yl)-1-phenyl-3,3a,4,9b-tetra-hydro-1H-chromeno[4,3-c]isoxazole-3a-carbo-nitrile.

In the title compound, C25H21BrN2O2, the fused isoxazolidine ring adopts an envelope conformation with the N atom at the flap and the mean plane of the ring makes dihedral angles of 54.37 (12) and 87.32 (13)°, respectively, with the adjacent phenyl and benzene rings. The tetra-hydro-pyran ring has a half-chair conformation. In the crystal, mol-ecules are linked into a double-column structure along the b-axis direction through weak C-H⋯O and C-H⋯π inter-actions.

rac-Methyl 3-(2-meth-oxy-phen-yl)-1-phenyl-3,3a,4,9b-tetra-hydro-1H-chromeno[4,3-c]isoxazole-3a-carboxyl-ate.

The title compound, C(25)H(23)NO(5), comprising two stereogenic carbon atoms of the same configuration, crystallizes in a centrosymmetric space group as a racemate. The six-membered pyran ring and the five-membered isoxazole ring adopt sofa and twisted conformations, respectively. The dihedral angle between the benzene ring and the mean plane through the near coplanar atoms of the pyran ring is 10.73 (7)°. The crystal structure features C-H⋯O hydrogen bonds.

(2S,5S,6R)-5-(4-Methyl-phen-yl)-3-phenyl-4,8-dioxa-3-aza-tricyclo-[7.4.0.0]trideca-1(13),9,11-triene-6-carbonitrile.

In the title compound, C(24)H(20)N(2)O(2), the six-membered pyran ring adopts a half-chair conformation with one C atom deviating from the mean plane of the remaining ring atoms by 0.654 (6) Å. The five-membered isoxazole ring adopts an N-envelope conformation with the N atom displaced by 0.742 (5) Šfrom the mean plane formed by the remaining ring atoms. The carbonitrile side chain is almost linear, with a C-C-N angle of 178.6 (5)°. The crystal packing is stabilized by inter-molecular C-H⋯N inter-actions, through bifurcated acceptor hydrogen bonds formed between the carbonitrile N atom and two alternate C atoms in the unsubstituted benzene ring. The mol-ecular structure and crystal packing are further stabilized by intra-molecular and inter-molecular C-H⋯π inter-actions.

(E)-2-({2-[(E)-(Hy-droxy-imino)-meth-yl]phen-oxy}meth-yl)-3-o-tolyl-acrylonitrile.

In the title compound, C(18)H(16)N(2)O(2), the dihedral angle between the mean planes through the two benzene rings is 56.8 (6)°. The enoate group assumes an extended conformation. The hy-droxy-ethanimine group is essentially coplanar with the benzene ring, the largest deviation from the mean plane being 0.047 (1) Šfor the hy-droxy-imino O atom. In the crystal, the mol-ecules are linked into cyclic centrosymmetric dimers with R(2) (2)(6) motifs via O-H⋯N hydrogen bonds.

rac-6-Eth-oxy-3,3a,4,9b-tetra-hydro-1,3-diphenyl-1H-chromeno[4,3-c]isoxazole-3a-carbonitrile.

The title compound, C(25)H(22)N(2)O(3), with three stereogenic centres, crystallizes in a centrosymmetric space group as a racemate. The pyran ring adopts a sofa conformation and the five-membered isoxazole ring exhibits an envelope conformation. The dihedral angle between the benzene ring and the mean plane through the near coplanar atoms of the pyran ring is 10.54 (9)°. In the crystal, no significant intermolecular interactions are observed.

(E)-2-({2-[(E)-(Hy-droxy-imino)-meth-yl]phen-oxy}meth-yl)-3-p-tolyl-acrylonitrile.

In the title compound, C(18)H(16)N(2)O(2), the hy-droxy-ethanimine group is essentially coplanar with the ring to which it is attached (C-C-N-O torsion angle = -176.9°). Mol-ecules are linked into cyclic centrosymmetric R(2) (2)(6) dimers via O-H⋯N hydrogen bonds.

Methyl (E)-2-({2-[(E)-(hy-droxy-imino)-meth-yl]phen-oxy}meth-yl)-3-phenyl-acrylate.

In the title compound, C(18)H(17)NO(4), the hy-droxy-ethanimine group is essentially coplanar with the ring to which it is attached [C-C-N-O torsion angle = 179.94 (14)°]. The mol-ecules are linked into cyclic centrosymmetric R(2) (2)(6) dimers via O-H⋯N hydrogen bonds and the crystal packing is further stabilized by C-H⋯O inter-actions.

(E)-Methyl 2-({2-eth-oxy-6-[(E)-(hy-droxy-imino)-meth-yl]phen-oxy}meth-yl)-3-phenyl-acrylate.

In the title compound, C(20)H(21)NO(5), the dihedral angle between the mean planes through the two rings is 47.1 (8)°. The enoate group assumes an extended conformation. The hy-droxy-ethanimine group is essentially coplanar with the benzene ring, the largest deviation from the mean plane being 0.061 (1) Šfor the O atom. In the crystal, mol-ecules are linked into cyclic centrosymmetric dimers with an R(2) (2)(6) motif via pairs of O-H⋯N hydrogen bonds. Inter-molecular C-H⋯O hydrogen bonds form a C(8) chain along the b axis. The crystal packing is further stabilized by C-H⋯π inter-actions.

Methyl (E)-2-({2-[(E)-(hy-droxy-imino)-meth-yl]phen-oxy}meth-yl)-3-(4-methyl-phen-yl)acrylate.

In the title compound, C(19)H(19)NO(4), the dihedral angle between the mean planes through the benzene rings is 82.18 (7)°. The C=N double bond is trans-configured. The mol-ecules are linked into centrosymmetric dimers via pairs of O-H⋯N hydrogen bonds with the motif R(2) (2)(6). The crystal packing also features C-H⋯O inter-actions. The methyl group attached to one of the aromatic rings is disordered over two almost equally occupied positions [occpancy ratio = 0.51 (4):0.49 (4)].

(E)-Methyl 3-(4-ethyl-phen-yl)-2-{2-[(E)-(hy-droxy-imino)-meth-yl]phen-oxy-meth-yl}acrylate.

In the title compound, C(20)H(21)NO(4), the two benzene rings are almost perpendicular to each other, making a dihedral angle of 86.1 (7)°. The hy-droxy-ethanimine group is essentially coplanar with the benzene ring, the largest deviation from the mean plane of the hy-droxy-ethanimine [C=N-OH] group being 0.011 (1) Šfor the O atom. An intra-molecular C-H⋯O hydrogen bond occurs. The mol-ecules are linked into cyclic centrosymmetric R(2) (2)(6) dimers via O-H⋯N hydrogen bonds. Inter-molecular C-H⋯O hydrogen bonds link the mol-ecules, forming a C(8) chain along the a axis. The crystal packing is further stabilized by C-H⋯π inter-actions.