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The chirality of the title compound, C(19)H(26)O(2), is solely generated by the presence of the double bond in the cyclo-hexene ring. This compound was synthesized to study the inter-action of the two enanti-omers in the solid state. The resultant racemate is made up of carboxylic acid RS dimers. Inter-molecular O-H⋯O hydrogen bonds produce centrosymmetric R(2) (2)(8) rings which dimerize the two chiral enanti-omers through their carboxyl groups.

The two components of the title heterodimer, C17H21NO2.C8H5NO2, are linked end-to-end via O-H...O(=C) and C-H...O(=C) hydrogen-bond interactions. Additional lateral C-H...O interactions link the dimers in a side-by-side fashion to produce wide infinite molecular ribbons. Adjacent ribbons are interconnected via pi-pi stacking and C-H...pi(arene) interactions. This structure represents the first evidence of robust hydrogen-bond formation between the moieties of pyridin-4(1H)-one and benzoic acid.

Cocrystallization of 1,1'-(p-phenylene)dipyridin-4(1H)-one (4,4'-dpy) and terephthalic acid (tpa) affords the hydrogen-bonded 1:1 title complex, C16H12N2O2.C8H6O4. Both molecules are symmetrically disposed about independent symmetry centers. Strong O-H...O hydrogen bonds between tpa carboxyl groups and 4,4'-dpy carbonyl groups produce one-dimensional zigzag infinite chains. Each chain is linked to four surrounding chains via weak C-H...O interactions, resulting in a three-dimensional molecular framework.

The title compound, C(21)H(24)N(3)O(4)P, is a self-complementary hydrogen-bond (HB) building unit, with (P=)O as the primary HB acceptor and N-H as the HB donor. Each of the four crystallographically distinct and nearly parallel molecules of the unit cell has a net dipole moment along the P=O bond direction and all of the dipoles are directed in the same general crystallographic direction. Head-to-tail N-H...O=P double-HB strands stack adjacent molecules into one-dimensional infinite polar columns. Each polar column is a 2(1) helix and all columns are essentially parallel, resulting in polar order throughout the entire crystal.

While the barriers of rotation of the sp and ap rotamers of 9-(o-methylphenyl)fluorene, C(20)H(16), are sufficiently similar to permit them to equilibrate, both being observed (NMR) in solution, crystallization provides the sp rotamer, (I), exclusively. Although in the sp conformation the intramolecular distance between adjacent C atoms of the phenyl and fluorene rings is small [3.382 (4) A, within 0.02 A of the sum of the van der Waals radii], in the ap conformation the distance between the adjacent o-CH(3) group on the phenyl ring and C atom of the fluorene ring would be much closer, based on that exhibited in the crystalline ap progenitor 9-(o-methylphenyl)-9-fluorenol. The angle between the fluorene and 9-aryl planes of (I) is 75.82 (10) degrees.

The title compound, C(20)H(16)O, (I), which crystallized exclusively as its ap rotamer, exhibits several intermolecular aryl-H.pi(arene) interactions, resulting in planar molecular arrays in which each molecule interacts with six adjacent molecules. Surprisingly, there were no O-H.O-H or O-H.pi(arene) interactions within hydrogen-bonding distances. Crystalline (I) melted sharply without molecular decomposition (NMR), but the cooled melt recrystallized only after several hours.

The title compound, C(23)H(22), (I), crystallizes in an ap conformationThe designations sp (synperiplanar) and ap (antiperiplanar) for these fluorene rotamers are in accordance with Rule E-6.6, IUPAC Tentative Rules, Section E, Fundamental Stereochemistry [J. Org. Chem. (1970), 35, 2861]. and its melt readily recrystallizes on cooling, in contrast to the corresponding 9-fluorenol compound, (II), which is sp and which melts without decomposition and fails to recrystallize over a long period. Both of these differences are ascribed to the intermolecular hydrogen bonding in (II), which is absent in (I) and which leads to distinctly different molecular packing in the two compounds.

The structure of the title compound, C(14)H(16)N(2)O(6)S(2).2C(6)H(6)O(2), consists of 2,2'-(4,4'-bipyridinium-1,1'-diyl)di(ethanesulfonate) molecules (with crystallographically imposed twofold symmetry) that are hydrogen bonded to each other, as well as to hydroquinone molecules, in a complex three-dimensional motif. The orange color of the crystals is indicative of the donor-acceptor interaction between the electron-rich hydroquinone pi-donor and the electron-deficient bipyridinium pi-acceptor. The dihedral angle between the bipyridyl planes is 38.31 (11) degrees. The distance from the centroid of one of the hydroquinone molecules to the center of the bipyridinium group is 3.653 (3) A, which is within the range typically observed for molecular complexes exhibiting charge-transfer characteristics.

The title compound, C(12)H(20)O(3), (IV), the ethyl ester of which is an intermediate in the synthesis of a compound reported to be highly estrogenic, has been prepared. After the initial steps reported for the synthesis of this ester intermediate were followed, it was converted into the crystalline acid, (IV), for X-ray analysis. It was verified that (IV) was racemic when prepared. X-ray analysis showed that anti-hydrogenation of the double bond had occurred in the synthesis, making the orientation of the carboxyl group cis to the 2-methyl group and trans to the 3-ethyl group. NMR spectroscopy showed that the stereochemistry of (IV) was identical with that of its ester precursor. While the earlier report did not note the stereochemistry of this ester, it pointed out that the estrogenic product derived from it possessed the opposite carboxyl-2-methyl orientation, i.e. trans, although no X-ray analysis was performed. In the light of these results and the importance of correlating biological activity with compound structure, the unequivocal characterization of the highly estrogenic compound is warranted.

Choristomas and mixed hamartomas of the oral cavity are uncommon lesions that show a variety of clinical presentations, histological appearances and growth patterns. We report a case of an unusual mixed hamartoma of the posterior tongue composed of dermoid cyst, sebaceous and glial elements. Magnetic resonance imaging indicated a predominantly cystic lesion limited to the pharyngeal and posterior part of the anterior tongue. A conservative approach was adopted and the lesion has shown minimal growth for 2 years following diagnosis.

The preparation of sp-9-acetylfluorene from the reaction of 9-fluorenyllithium with acetyl chloride also provided 9-(1-acetoxyethylidene)fluorene ('diacetylfluorene') and 1,1-di(9-fluorenyl)ethanol, (II), as by-products recently characterized by X-ray analysis. A third by-product, 1,1-di(9-fluorenyl)ethyl acetate, (III), C(30)H(24)O(2), has now been unequivocally identified for the first time, and emanates from the acetylation of the oxyanion of (II). In the asymmetric unit, compound (III) exists as two almost identical structures which differ slightly, but significantly, in conformation. Neither possesses the significant fluorene-ring bowing or the perpendicularity of the two ring planes exhibited by (II). The angle between the least-squares planes of the two fluorene rings of (III) is 58.45 (9) and 60.95 (10) degrees, respectively, for the two conformations, and their corresponding bonding parameters also differ slightly in a number of instances.

Treatment of 9-fluorenyllithium with acetyl chloride produces 9-acetylfluorene, (I), and several by-products. Among them is a compound unequivocally identified for the first time as the addition product of (I) with 9-fluorenyllithium, 1,1-di(9-fluorenyl)ethanol, C(28)H(22)O, (II). The two fluorene-ring planes of (II) are essentially perpendicular [89.90 (9) degrees ]. A number of intermolecular non-bonding distances are well within or close to the sum of their respective van der Waals radii and may be responsible for the rarely observed large bowing of one of the fluorene rings. This bowing apparently arises from two molecules impinging on the convex face of the bowed ring, augmented by hydrogen bonding between the peripheral pi electrons of the concave face and the hydroxyl H atom of another molecule adjacent to that face.

Treatment of 9-fluorenyllithium with acetyl chloride produces 9-acetylfluorene, (I), and several by-products, among which is "diacetylfluorene", now characterized definitively as 9-(1-acetoxyethylidene)fluorene [IUPAC name: (1-fluoren-9-ylidene)ethyl acetate], (II), C(17)H(14)O(2), derived from acetylation of initially formed (I). Various parameters disclose substantial structural distortion within (II) emanating from A((1,3)) strain associated with the 9-(acetoxyethylidenyl)fluorene system.

The title compound, C(14)H(20)O(8), was synthesized from the hydrogenation of tetramethyl 1,4-cyclohexadiene-1,2,4, 5-tetracarboxylate with a catalytic amount of palladium/carbon. All four carbonyl moieties of the methyl ester groups are on the same face of the chair-conformed ring. The substantial ring distortion associated with the 1,3-diaxial methoxycarbonyl substituents is reflected in the large difference between bond angles as well as torsion angles, respectively, that in undistorted cyclohexanes would be approximately the same.

Methylation of 9-lithiated ap-9-pivaloylfluorene, (I), as well as pivaloylation of 9-lithiated 9-methylfluorene provided rotationally stable sp-9-methyl-9-pivaloylfluorene, (III), C(19)H(20)O, which lies about a crystallographic mirror plane. Fluorene (I) exists exclusively in the ap configuration in solution (NMR) as well as in the crystalline state, reflecting the unfavorable interaction between the tert-butyl and fluorene-ring pi electrons in the sp configuration. The existence of (III) exclusively in the sp configuration indicates that, in this case, the interaction between the tert-butyl group and the fluorene-ring pi electrons provides relatively more thermodynamic stability than the steric interaction between the tert-butyl and 9-methyl groups (ap configuration).

Treatment of 9-lithiated fluorene with pivaloyl chloride provided ap-9-pivaloylfluorene, (1), the major product, and a minor product ultimately identified as the title compound, C(23)H(26)O(2), (2). The latter was also formed directly, but slowly, from 9-lithiated-(1) treated with pivaloyl chloride. Although (1) exists exclusively as its less sterically restricted ap rotamer, its sp(2)-hybridized anion sterically impedes reaction at the 9-position from either face. While 9-lithiated-(1) is exclusively, but slowly, 9-methylated with methyl iodide, reaction with pivaloyl chloride, also slow, leads only to the O-acylated product, (2). The protons of the tert-butyl-C=C moiety approach a proton on the fluorene ring to well within the sum of their van der Waals radii, resulting in significant molecular compression, strain and distortion. For example, distortion in the moiety C=C(O)(C) is exhibited by the enlargement of C=C-C angle to 130.6 (2) degrees at the expense of the corresponding 'equivalent' C=C-O angle, which is compressed to 116.46 (19) degrees.

A prototype of a new class of 2,3,1-benzodiazaborine-based estrogen mimics is described. 1,2-Dihydro-1,6-dihydroxy-2-(2-methoxy-6-pyridyl)-2,3,1-benzodiazabor ine, (6), was obtained as a crystalline monohydrate (C13H12BN3O3.H2O) after regioselective BBr3-mediated O-demethylation of the condensation product formed from 2-formyl-4-methoxybenzeneboronic acid and 2-hydrazino-6-methoxypyridine. As intended by design, the solid-state structure of (6) features an intramolecular hydrogen-bond association between the donor B--OH group and the acceptor pyridine ring N, a connection which constitutes an additional 'virtual' six-membered ring, thereby providing for an overall topography closely matching that of a tetracyclic steroid. Specifically, prototype (6) can be viewed as a boron-containing mimic of the O17-methyl ether derivatives of dihydroequilenin or estradiol.

The condensation reaction of 4-amino-6-methyl-2-pyrone with 1-cyclohexenecarboxaldehyde and a catalytic amount of (S)-(+)-10-camphorsulfonic acid in toluene at 358 K gave a 1:2.5 ratio of the title compound, (1) (C13H13NO2), and 7,8,9,10-tetrahydro-1H-pyrano[4,3-c]isoquinoline-1-one, (2). The formation of (2) presumably proceeds through an intermediate imine. Both (1) and (2) show inhibitory activities against acetylcholinesterase and human aldose reductase. Of the three linear-fused rings of (1), both ring A and ring B are planar and the angle between these planes is 0.46 (13) degrees. While the two C atoms of cyclohexane ring C attached to its common atoms with ring B are in the plane of the latter, as expected, the remaining two C atoms of ring C are out of this plane, by 0.342 (4) and -0.402 (3) A, respectively.

The structure of the fourth member of a family of structurally related 2,3,1-benzodiheteroborines has been solved by crystallographic means, providing data for proper direct comparison with the others. The title compound, 1,2-dihydro-1-hydroxy-2-methyl-2,3,1-benzodiazaborine (C8H9BN2O) is obtained via condensation of 2-formylbenzeneboronic acid and methylhydrazine, and is similar in most respects to its 2-unsubstituted parent, in internal geometry and intramolecular association topography, but has some subtle oxazaborine-like characteristics.

Condensation of 2-formylbenzeneboronic acid and 1,1-dimethylhydrazine afforded the title compound, bis(8-B-4)-1,3,5-tris[2-[(N,N-dimethylhydrazono)methyl]-phenyl)]b oroxin, C27H33B3N6O3, a tridehydro cyclic trimer of the expected simple benzaldehyde hydrazone and the first triphenylboroxin derivative found to possess two B chelating interactions. The double chelation induces molecular asymmetry but effects only a slight puckering in the central boroxin ring.

The title compound, C16H21NO2S, isolated from the reaction of lithiated racemic 2,3,4,4a,5,6,7,8-octahydroquinoline with 0.5 equivalents of (-)-(1R,2S,5R)-menthyl (SS)-p-toluenesulfinate, possesses the unusual conformation in which the OH and bulky p-toluenesulfinyl groups are in axial positions. The S=O bond distance of 1.519 (3) A is longer than expected because of intramolecular hydrogen bonding between the hydroxyl group and the sulfinyl O atom.

The title compound, derived in four steps beginning with the cyclopropanation reaction of the anion of the alpha-sulfinyl ketimine (4R,SS)-4-(tert-butyldimethylsilyloxy)-3,4-dihydro-5-(p-tolysul finyl)methyl)-2H-pyrrole with 2-chloroethyl trifluoromethanesulfonate, contains a shorter than expected bond (C(7)--C(8) 1.48(l) A) and a larger than expected angle (S(1)--C(6)--C(2) 123.2(6) in the cyclopropane framework.

C18H19O3P, M(r) = 314.32, monoclinic, P2(1)/n, a = 5.726 (6), b = 14.234 (7), c = 20.08 (1) A, beta = 92.54 (7) degrees, V = 1635 (4) A3, Z = 4, Dx = 1.277 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 1.71 cm-1, F(000) = 664, T = 296 K, R = 0.042, 1813 unique observed reflections. The X-ray structure determination of the title compound shows that the dioxaphosphorinane ring has a chair conformation in which the phosphoryl O atom (P=O) is equatorial, which explains the absence of substantial NMR deshielding by its P=O group on H(4) and H(6), which are axial.

1-(9-Hydroxyfluoren-9-yl)-2,2-dimethyl-1-propanone, C18H18O2, M(r) = 266.34, orthorhombic, Pbcn, a = 18.917 (10), b = 11.843 (8), c = 13.177 (7) A, V = 2952 (5) A3, Z = 8, Dx = 1.198 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 0.72 cm-1, F(000) = 1136, T = 296 K, R = 0.044 for 1042 unique observed reflections. Conversion of ap-9-pivaloylfluorene, ap-(I), into lithiated (I)-9-anion followed by the addition of MeOH, then H2O, led to unexpected hydroxylation to provide 20-40% of sp-9-hydroxy-9-pivaloyfluorene, sp-(II), and 60-80% recovery of ap-(I). The singular sp conformation of (II) in solution suggested by NMR was confirmed in the crystalline state by X-ray diffraction which showed the O(1)-C(9)-C(10)-O(2) torsion angle approximately 0 degrees and the C(10) = O(2)...H(9)-O(1) non-bonding distance 1.95 (4) A, suggesting strong intramolecular hydrogen bonding in this conformation.

The title compound contains the tetracyclic A-B-C-E ring system of cephalotaxus alkaloids. Unexpectedly, the five-membered-ring plane is twisted 67.2 degrees from the aromatic ring plane and, like cephalotaxine, the seven-membered ring is oriented in a boat form with the nitrogen at the prow.

C15H15NOS, Mr = 257.35, monoclinic, P2(1), a = 7.710 (2), b = 5.903 (5), c = 14.700 (3) A, beta = 91.48 (2) degrees, V = 668.8 (6) A3, Z = 2, Dx = 1.278 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 2.18 cm-1, F(000) = 272, T = 296 K, R = 0.043, 944 unique observed reflections. This is the first structure determination of an N-alkylidenesulfinamide. The C = N bond is distorted and lengthened presumably because of the steric interaction and electron-withdrawing effect of the sulfinyl group. The nonplanar conformation is also a result of repulsive steric interaction. The configuration at C = N is trans. The title compound was obtained from the displacement reaction of (-)-1-methyl (S)-p-toluenesulfinate with methyllithium.

C16H19NO2S, Mr = 289.39, orthorhombic, P2(1)2(1)2(1), a = 11.467 (5), b = 17.207 (8), c = 7.566 (4) A, V = 1493 (2) A3, Z = 4, Dx = 1.29 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 2.07 cm-1, F(000) = 616, T = 296 K, R = 0.049, 928 unique observed reflections. The structure determination combined with the known S configuration at the sulfur site discloses the stereochemistry of the title compound to be 7S and SS.