Aryl imines formed in situ from aryl aldehydes and aromatic amines undergo smooth [4 2] cycloaddition reactions with cyclic enol ethers such as 3,4-dihydro-2H-pyran and 2,3-dihydrofuran in the presence of 10 mol % Selectfluor TM in acetonitrile at room temperature to afford pyrano-and furanotetrahydroquinoline derivatives in excellent yields with high endo-selectivity.

D-Glycals undergo smoothly allylic rearrangement with allyltrimethylsilane and trimethylsilyl cyanide in the presence of catalytic amount of bismuth triflate to afford the corresponding 2,3-unsaturated allyl glycosides and glycosyl cyanides in excellent yields with high a-selectivity.

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The molecule of the title compound C19H18O6, adopts anEconformation about the C=C double bond and the C—C=C—C torsion angle is −179.30 (16)°. The molecule is nearly planar, as indicated by the dihedral angle of 6.99 (6)° between the benzene ring and the benzodioxalane ring. In the crystal, molecules are linkedviaweak C—H...O hydrogen bonds, forming zigzag chains propagating along thebaxis.

In the title compound, C18H13F2NO2, the two rings of the quinoline system are fused almost coaxially, with a dihedral angle between their planes of 2.28 (8)°. The plane of the attached benzene ring is inclined to the plane of the quinoline system by 7.65 (7)°. The carboxyl­ate group attached to the quinoline system is in an anti­periplanar conformation. There is a short intra­molecular C—H⋯O contact involving the carbonyl group. In the crystal, mol­ecules are linked via C—H⋯O hydrogen bonds, forming chains lying in the (1-10) plane.

In the title compound, C 16 H 20 N 4 O, the dihedral angle between the pyrazole and phenyl rings is 53.86 (12) . The piperazine ring adopts a chair conformation with the exocyclic N-C bonds in equatorial orientations. In the crystal, molecules are linked by very weak C-HÁ Á ÁO hydrogen bonds to generate [010] C(8) chains, with adjacent molecules related by translation. Structure descriptionPiperazine derivatives are found in biologically active compounds across many therapeutic areas and display antipsychotic (Chaudhary et al., 2006) and antifungal (Upadhayaya et al., 2004) behaviours. As part of our ongoing studies in this area (Girisha et al., 2010), herein we report the synthesis and structure of the title compound (Fig. 1).The dihedral angle between the pyrazole (r.m.s. deviation = 0.012 Å ) and phenyl rings is 53.86 (12) . The piperazine ring adopts a chair conformation with the exocyclic N-C bonds in equatorial orientations. The piperazine ring bisects the plane of the pyrazole ring which is evident from the dihedral angle value of 53.57 (10) between the mean planes of the pyrazole and piperazine (all atoms) rings.In the crystal, the molecules are linked by weak C-HÁ Á ÁO hydrogen bonds (Table 1) to generate [010] C(8) chains, with adjacent molecules related by translation (Fig. 2).

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