Methyl 7,8-diacetoxy-11-oxo-5-(2-oxopyrrolidin-1-yl)-7,9-epoxycyclopenta[4,5]pyrido[1,2-a]quinoline-10-carboxylate sesquihydrate

The title compound, C26H28N2O9·1.5H2O, the product of an acid-catalysed Wagner–Meerwein skeletal rearrangement, crystallizes as a sesquihydrate with the O atom of one of the two independent water molecules occupying a special position on a twofold axis. The organic molecule comprises a fused pentacyclic system containing two five-membered rings (cyclopentane and tetrahydrofuran) and three six-membered rings (piperidinone, tetrahydropyridine and benzene). The five-membered rings have the usual envelope conformations, and the central six-membered piperidinone and tetrahydropyridine rings adopt boat and sofa conformations, respectively. In the crystal, there are three independent O—H⋯O hydrogen bonds, which link the organic molecules and water molecules into complex two-tier layers parallel to (001). The layers are further linked into a three-dimensional framework by attractive intermolecular carbonyl–carbonyl interactions.

The title compound, C 26 H 28 N 2 O 9 Á1.5H 2 O, the product of an acid-catalysed Wagner-Meerwein skeletal rearrangement, crystallizes as a sesquihydrate with the O atom of one of the two independent water molecules occupying a special position on a twofold axis. The organic molecule comprises a fused pentacyclic system containing two five-membered rings (cyclopentane and tetrahydrofuran) and three six-membered rings (piperidinone, tetrahydropyridine and benzene). The five-membered rings have the usual envelope conformations, and the central six-membered piperidinone and tetrahydropyridine rings adopt boat and sofa conformations, respectively. In the crystal, there are three independent O-HÁ Á ÁO hydrogen bonds, which link the organic molecules and water molecules into complex two-tier layers parallel to (001). The layers are further linked into a three-dimensional framework by attractive intermolecular carbonyl-carbonyl interactions.
The structure of methyl 7,8-bis(acetyloxy)-11-oxo-5-(N-pyrrolidonyl)-7,9-epoxycyclopenta[4,5]pyrido[1,2-a]quinoline-10-carboxylate (I) was established by X-ray diffraction study (Fig. 1). Compound (I) crystallizes as sesquihydrate, i. e., C 26 H 28 N 2 O 9 .1.5H 2 O; one of the two independent water molecules occupies a special position on the twofold axis. Molecule of (I) comprises a fused pentacyclic system containing two five-membered rings (cyclopentane and tetrahydrofuran) and three six-membered rings (piperidinone, tetrahydropyridine and benzene). Both five-membered rings of the bicyclic fragment have usual envelope conformations, and the central six-membered piperidinone and tetrahydropyridine rings adopt the boat and sofa conformations, respectively. The nitrogen N12 atom has a trigonal-planar geometry (sum of the bond angles is 359.5°). The dihedral angle between the planes of the piperidinone (or rather "bottom of the boat" C6A, C7, C10A, C11 plane) and benzene is 38.81 (3)°. The two carboxylate substituents at the C7 and C8 carbon atoms are in the sterically unfavorable syn-periplanar configuration relative to the tetrahydrofuran ring. Such disposition is explained by the direction of the Wagner-Meerwein rearrangement.
The pyrrolidinone ligand and carboxylate substituent at the C10 atom are on the same side of the core pentacyclic framework. It is noteworthy that these fragments are engaged in the attractive intermolecular carbonyl-carbonyl interactions Carbonyl-carbonyl interactions of such type were investigated in substantial detail by Allen et al. (1998).
The mixture was stirred for 2 h at 296 K, then it was diluted with 100 ml of water and treated with a saturated solution of sodium carbonate until pH ~ 8-9. Organic products were extracted with chloroform (3 x 50 ml). The extract was dried (MgSO 4 ), concentrated and purified by crystallization from hexane-ethyl acetate to give 0.41 g (0.8 mmol) of the polycycle (I) as colourless rhomboid-shaped blocks (Fig. 3). Yield is 67%. The single crystals of product (I) were obtained by slow crystallization from a mixture of 95% ethanol-DMF (yield 30%

Refinement
The hydrogen atoms of the solvate water molecules were located in the difference Fourier map; C-bound H atoms were placed geometrically (C-H 0.95 Å, 0.98 Å, 0.99 Å, and 1.00 Å for aromatic, methyl, methylene and methine H atoms respectively) and included in the refinement in riding motion approximation [U iso (H) = 1.2U eq (C) for non-methyl H atoms;