Substituents In Equatorial Positions Research Articles

Stability of Hierarchically Formed Titanium(IV) Tris(catecholate ester) Helicates with Cyclohexyl Substituents in DMSO.

A cyclohexyl substituent strongly prefers the chair conformation with large substituents in equatorial positions, while other cycloalkyls are structurally more flexible. In hierarchically formed dimeric titanium(IV) tris(catecholates) equatorial versus axial connection of the cyclohexane to the ester results in either a more compact (axial) or more expanded (equatorial) structure. In DMSO solution the axial position results in a compact structure which minimizes solvophobic effects, leading to higher stability. However, computational investigations indicate that additionally intramolecular London dispersion interactions significantly contribute to the stability of the dimer. Thus, weak side-chain-side-chain interactions are responsible for the high stability of cyclohexyl ester derivatives with axial compared to equatorial ester connection.

Tert-Butyl 4-(3,4-dichloroanilino)piperidine-1-carboxylate

In the title compound, C16H22Cl2N2O2, the substituted piperidine ring adopts a chair conformation with both substituents in equatorial positions. In the crystal, N—H⋯O and C—H⋯O hydrogen bonds connect mol­ecules into ribbons along the a-axis direction.

2,8,9-Tris(2-methylpropyl)-2,5,8,9-tetraaza-1λ5-phosphatricyclo[3.3.3.01,5]undecan-5-ium chloride dihydrate

The asymmetric unit of the title hydrated salt, C18H40N4P+·Cl−·2H2O, consists of two ionic mol­ecules and four water mol­ecules. The mol­ecular geometry around the penta­coordinate P atom is trigonal–bipyramidal, with a H atom and an apical N atom in axial positions and three N atoms with isobutyl substituents in equatorial positions. The Cl− ions and water mol­ecules are connected via O—H⋯Cl hydrogen bonds, forming chains along [100]. The ethyl­ene bridging groups are disordered with refined site-occupancy ratios of 0.578 (9):0.422 (9).

1,2,3,4,5,6-Hexa-O-acetyl-scyllo-inositol

The title mol­ecule, C18H24O12, has crystallographic 2/m symmetry with two acetate group located on a mirror plane. The H—Csp 3—O—Csp 2 torsion angles characterizing orientation of the acetyl groups with respect to the cyclo­hexane ring are 0.0, 23.9 and −23.9°. The cyclo­hexane ring is in a chair conformation with all substituents in equatorial positions. In the crystal, mol­ecules are connected through C—H⋯O hydrogen bonds into a chain extending along the c axis.

1-(2-Chlorobenzyl)-3-methyl-2,6-diphenylpiperidine

In the title compound, C25H26ClN, the piperidine ring has a chair conformation with all ring substituents in equatorial positions. The dihedral angle formed between the chloro­benzene ring and the flanking phenyl rings are 74.91 (18) and 47.86 (17)°. The chloro substituent is anti to the piperidine N atom. In the crystal, centrosymmetrically related mol­ecules aggregate via π–π inter­actions occurring between chloro­benzene rings [centroid–centroid distance = 3.778 (2) Å] and these are linked into linear supra­molecular chains along the a axis by C—H⋯π inter­actions occurring between the phenyl rings.

2,2'-(Piperazine-1,4-di-yl)diacetonitrile.

The complete mol­ecule of the title compound, C8H12N4, is generated by a crystallographic inversion centre. The piperazine ring adopts a chair conformation with the N-bonded substituents in equatorial positions. In the crystal, mol­ecules are linked by C—H⋯Nc (c = cyanide) hydrogen bonds.

2-Chloro-1-[4-(2,4-difluorobenzyl)piperazin-1-yl]ethanone

In the title mol­ecule, C13H15ClF2N2O, the piperazine ring is in a chair conformation with the 2,4-difluoro­benzyl and chloro­acetyl substituents in equatorial positions.

2-Deoxy-α-D-arabino-hexopyranose

The title compound, C6H12O5, is the α-pyran­ose form of the reducing aldose 2-de­oxy-d-arabino-hexose. The six-membered pyran­ose ring adopts a 4 C 1 conformation, with the anomeric hy­droxy group in axial and the other substituents in equatorial positions. In the crystal, each of the four hy­droxy groups acts as an inter­molecular hydrogen-bond donor function, resulting in a three-dimensional hydrogen-bonded network.

2-Phenylethyl 1-thio-β-D-galactopyranoside hemihydrate

The title compound, C14H20O5S·0.5H2O, crystallizes with two organic mol­ecules and a solvent water mol­ecule in the asymmetric unit. In both mol­ecules, the hexa­pyranosyl rings adopt a slightly distorted chair conformation (5 C 2) with four substituents in equatorial positions and one substituent in an axial position. The main difference between the organic mol­ecules is the dihedral angle between the phenyl ring and the best plane defined by the O—C1—C2—C3 atoms (r.m.s deviations = 0.003 and 0.043 Å) of the hexa­pyranosyl rings [47.4 (4) and 86.5 (4)°]. In the asymmetric unit, mol­ecules are linked by two strong O—H⋯O hydrogen bonds. In the crystal, the components are linked by a total of 10 distinct O—H⋯O hydrogen bonds, resulting in the formation of a two-dimensional network parallel to the ab plane.

3,9-Diisopropyl-2,4,8,10-tetrathiaspiro[5.5]undecane

The mol­ecule of the title compound, C13H24S4, has C2 symmetry and it crystallizes as a racemate. The structure displays two six-membered rings exhibiting chair conformations, with the isopropyl substituents in equatorial positions. In the crystal structure, weak inter­molecular C—H⋯S inter­actions are observed, leading to a channel-like arrangement along the c axis.

3,5-Dimethyl-2,6-diphenyl-3,4,5,6-tetrahydro-2H-pyran-4-one

The mol­ecular structure of the title compound, C19H20O2, reveals a slightly distorted chair conformation for the tetra­hydro­pyran ring with the two methyl and two phenyl substituents in equatorial positions.

Trans-4-[(Phenylsulfonyloxy)methyl]cyclohexanecarboxylic acid

The title compound, C14H18O5S, is an important inter­mediate for the synthesis of poly(amido­amine) dendrimers. The cyclo­hexane ring adopts a chair conformation with its two substituents in equatorial positions. In the crystal structure, mol­ecules form centrosymmetric dimers via O—H⋯O hydrogen bonds.

2,3,4,6-Tetra-O-acetyl-α-D-glucopyranosyl azide

The CuI-catalysed 1,3-dipolar cyclo­addition of an azide and a terminal alkyne is becoming an increasingly popular tool for synthetic chemists. This is the most representative of the so-called `click reactions' and it is used to generate 1,4-di­substituted triazoles in high yield. During studies on such cyclo­addition reactions, a reduced reactivity of an α-glucosyl azide with respect to the corresponding β-anomer was observed. With the aim of understanding this phenomenon, the structure of the title compound, C14H19N3O9, has been determined at 140 K. The glucopyranosyl ring appears in a regular 4C1 chair conformation with all the substituents in equatorial positions, except for the anomeric azide group, which adopts an axial orientation. The observed bond lengths are consistent with a strong anomeric effect, which is reflected in a change in dipolar character and hence reduced reactivity of the α-glucosyl azide.

2,4-Bis(4-chlorobenzoyl)-1-(4-chlorophenyl)-3,5-di-2-thienylcyclohexanol methanol hemisolvate

The title compound, C34H25Cl3O3S2·0.5CH3OH, was synthesized by the reaction of thio­phene-2-carbaldehyde with acetophenone and NaOH under solvent-free conditions, using tetra­butylammonium bromide as a phase-transfer catalyst. The central six-membered ring adopts a chair conformation with the bulky thio­phene, 4-chloro­phenyl and 4-chloro­benzoyl substituents in equatorial positions. The hydroxyl group is in an axial position and forms an intra­molecular O—H⋯O hydrogen bond to the carbonyl group of an adjacent 4-chloro­benzoyl substituent. The methanol solvent mol­ecules are disordered equally over two positions within one-dimensional channels, with site occupancy factors of 0.25.

A Cyclopropane Fragmentation Approach to Heterocycle Assembly: A Convergent Synthesis of Oxepanes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A Cyclopropane Fragmentation Approach to Heterocycle Assembly: A Convergent Synthesis of Oxepanes

[reaction: see text] A cyclopropanol fragmentation approach to the synthesis of oxepanes has been developed. This convergent strategy condenses cyclopropyl diols with aldehydes to form an acetal, which is subsequently rearranged to furnish a keto-oxepane. The reaction has been developed as a one-pot procedure, utilizing sequential addition of Al(OTf)3 and TiCl4. Yields range from 50 to 70% for the sequence. A Zimmerman-Traxler transition state disposing substituents in equatorial positions is consistent with the observed formation of strictly cis products.

Prop-2-ynyl 1,2,3,4-tetra-O-acetyl-β-D-glucopyranuronate

The structure of the title compound, C17H20O11, has been determined by single-crystal X-ray diffraction at 100 K. The glucopyranose ring exhibits a chair conformation, with all non-H-atom substituents in equatorial positions, and the triple bond is sterically easily accessible, allowing for followup cycloaddition reactions. The glucopyranose ring exhibits chair conformation with all non-H substituents in equatorial positions, and the triple bond is sterically easily accessible, allowing for follow-up cycloaddition reactions.

4-Methoxybenzaldehyde 4-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)thiosemicarbazone

In the title compound, C23H29N3O10S, the hexa­pyran­osyl ring adopts a chair conformation with all the substituents in equatorial positions. The mol­ecules are linked by C—H⋯S interactions into ribbons parallel to the a axis and two additional intermolecular C—H⋯O interactions provide further stability in a three-dimensional network.

Synthesis and characterization of 2,5,7-trichalcogena-1,3,4,6-tetrasilanorbornanes (RMeSiSiMe) 2E 3 (R=Me, Ph/E=S, Se, Te)

The reactions of the trichlorodisilanes ClRMeSi–SiMeCl 2 (R=Me, Ph) with either H 2S/NEt 3 or Li 2E (E=Se, Te) result in the selective formation of 2,5,7-trichalcogena-1,3,4,6-tetrasilanorbornanes (RMeSiSiMe) 2E 3 (R=Me, Ph/E=S, Se, Te). In the cases of R=Ph, three stereoisomers with different spatial orientations of the phenyl substituents arise. The isomers with both phenyl substituents in equatorial positions are formed preferably. All products have been characterized by multinuclear NMR spectroscopy including 1 J SiSe and 1 J SiTe coupling constants. A crystal structure analysis of the isomer of (PhMeSiSiMe) 2S 3 with both phenyl substituents in equatorial positions reveals a very small bond angle at the bridging sulfur atom of 88.5° which is even 4.6° smaller than in the parent norbornane C 7H 12.

Synthesis, structural characterization and 57Fe-Mössbauer spectra of ferrocenylhexasilanes

Linear and cyclic ferrocenylhexasilanes 1,6-Fc–Si 6Me 12–X [X=Me, –C 6H 4CHC(CN) 2], 1,3- and 1,4-Fc–Si 6Me 10–X [X=Me, –C 6H 4CHC(CN) 2], have been synthesized and their Mössbauer spectra have been measured. All compounds possess localized electronic structures on the Mössbauer timescale and partial Fe(III) character of the iron atom due to Cp→(Si n ) electron transfer. The Mössbauer data obtained, furthermore, indicate considerable aryl–ferrocenyl interaction via the hexasilane moiety. The single crystal X-ray structures of 1,3- and 1,4-Fc–Si 6Me 10–C 6H 4CHC(CN) 2 exhibit the cyclohexasilane ring in chair conformation with the bulky Fc- and aryl substituents in equatorial positions.