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Optically active liquid-crystalline fullerodendrimers from enantiomerically pure fulleropyrrolidines
A synthetic methodology based on the 1,3-dipolar cycloaddition reaction was developed to design enantiomerically pure liquid-crystalline fullerodendrimers.
4,4-Bis(1H-pyrrol-2-yl)pentanol
The title achiral compound, C13H18N2O, crystallized in the chiral monoclinic space group P21. The pyrrole rings are inclined to one another by 62.30 (11)°, and the propanol chain is in an extended conformation. In the crystal, the two pyrrole NH groups are involved in intermolecular N-H ··· O hydrogen bonds, leading to the formation of a helical arrangement propagating along the b axis. An interesting feature of the crystal structure is the absence of any conventional hydrogen bonds involving the hydroxy H atom. There is, however, a weak intermolecular O-H ··· π interaction involving one of the pyrrole rings.
Synthesis, Structure, and Complexation Properties of Partially and Completely Reduced meso-Octamethylporphyrinogens (Calix[4]pyrroles)
Rac-(2R*,3R*)-S-Ethyl-4-Chloro-3-Hydroxy-2-Phenylbuthanethioate and Rac-(2R*,3R*)-S-Ethyl-2-Phenyl-3-(tosyloxy)buthanethioate: Dichotomy of the Stereoselectivity of the Mukaiyama Reaction
The title compounds, rac-(2R*,3R*)-S-ethyl-4-chloro-3-hydroxy-2-phenylbuthanethioate (I) and rac-(2R*,3R*)-S-ethyl-2-phenyl-3-(tosyloxy)buthanethioate (III), are both composed of a S-ethyl 2-phenylbutanethioate moiety but have different geometries. Compound I is substituted in the 3 and 4 positions by a hydroxyl group and a chlorine atom, respectively. In compound III the hydroxyl group in the 3 position of rac-(2R*,3R*)-S-ethyl-3-hydroxy-2-phenylbuthanethioate (II), has been tosylated in order to obtain suitable crystals for X-ray analysis. In compound I the phenyl substituent and the hydroxyl group have a syn arrangement, whereas in the tosylate derivative of II, i.e., compound III, they have an anti arrangement. In the crystal structure of I centrosymmetric hydrogen bonded dimers are formed via O–H•••O hydrogen bonds, involving the hydroxyl group and the carbonyl O-atom. In the crystal structure of III symmetry related molecules are connect via a weak C–H•••O intermolecular interaction, involving a tosylate O-atom and a phenyl H-atom, so forming zigzag chains propagating in the c direction. The compounds were prepared by the Mukaiyama crossed aldol reaction between the silyl enol ether of S-ethyl 2-phenylethanethioate and simple aldehydes, like 2-chloroacetaldehyde (for I) and acetaldehyde (for II). The syn/anti stereo descriptors clearly indicate that the stereoselectivity of the Mukaiyama aldol reaction has switched from a syn selective process for the reaction using 2-chloroacetaldehyde to an anti selective process for the reaction with acetaldehyde. In both compounds the relative stereochemistry at the newly created chiral centers, positions 2 and 3, is R/R.
2,2'-(Propane-2,2-diyl)bis(1H-pyrrole)
The title compound, C11H14N2, crystallized with two independent molecules (A and B) in the asymmetric unit. The two molecules differ only slightly, with the pyrrole rings being inclined to one another at a dihedral angle of 87.67 (8)° in molecule A and 88.09 (7)° in molecule B. In the crystal, there are no classical hydrogen bonds, but the two pyrrole NH groups of one molecule are involved in N-H ··· π interactions with the pyrrole rings of the other molecule. In this manner, a compact box-like arrangement of the two independent molecules is formed.
Catalytic Hydrogenation of meso-Octamethylporphyrinogen (Calix[4]pyrrole)
Hydrogenation of meso-octamethylporphyrinogen (calix[4]pyrrole) with a number of heterogeneous catalysts under different experimental conditions has been investigated. GC-MS analyses of the reaction mixtures showed the formation of one to four products in low to moderate yields: three of them were diastereoisomers of the product derived from half-hydrogenation of the substrate, and displayed alternating pyrrolidine and pyrrole rings, while the fourth was the all-cis saturated product. An acidic medium was necessary to achieve hydrogenation. However, the use of too strongly acidic solvents or additives was detrimental to the stability of the substrate and/or the catalyst.
rac-Methyl 4-azido-3-hydroxy-3-(2-nitrophenyl)butanoate
In the title compound, C11H12N4O5, the mean plane through the nitro substituent on the benzene ring is inclined to the benzene mean plane by 85.8 (2)°, which avoids steric interactions with the ortho substituents. The hydroxy group is involved in bifurcated hydrogen bonds. The first is an intramolecular O-H···O hydrogen bond, involving the ester carbonyl O atom, which gives rise to the formation of a boat-like hydrogen-bonded chelate ring. The second is an intermolecular O-H···N hydrogen bond involving the first N atom of the azide group of a symmetry-related molecule. In the crystal structure this leads to the formation of a polmer chain extending in the c-axis direction.
2-(2-Naphthyl)-1,3-dioxane
The title compound, C14H14O2, crystallizes in the chiral monoclinic space group P21. This acetal is composed of a planar naphthalene ring with a 1,3-dioxane ring substituent, which has a chair conformation. In the crystal structure, symmetry-related molecules are connected via a weak C-H ··· O interaction to form a helical chain propagating in [010]. While there are no - stacking interactions present, there are weak C-H ··· π interactions involving the naphthalene aromatic rings, which link the helical chains to form a two-dimensional network in the (011) plane.
Preparation of donor–acceptor substituted fluorostilbenes and crystal chemistry of fluorinated (E)-4-(4-halogeno-styryl)-benzonitriles
The syntheses and crystal structures of a series of fluoro-substituted halogeno (Cl, Br, I)-cyano-stilbenes containing donor and acceptor groups (D-π-A) are reported. These molecules show a tendency to form antiparallel chain-like structures and herringbone packing, crystallising predominantly in a centric space group. However, second harmonic generation measurements bear evidence for orientational disorder leading to partial polar order below the ordinary X-ray structure determination limit. Some co-crystals are isostructural with their components. The non-fluoro as well as the halogeno-fluoro substituted components of co-crystals seem to impose their crystal structure on the complementary fluoro- or cyano–fluoro substituted components. Co-crystallization enhanced the deviation from centrosymmetry.
5-Hydroxyalkyl derivatives of tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate: diastereoselectivity of the Mukaiyama crossed-aldol-type reaction
The title compounds, rac-(1'R,2R)-tert-butyl 2-(1'-hydroxyethyl)-3-(2-nitrophenyl)-5-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate, C17H20N2O6, (I), rac-(1'S,2R)- tert-butyl 2-[1'-hydroxy-3'-(methoxycarbonyl)propyl]-3-(2-nitrophenyl)-5-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate, C20H24N2O8, (II), and rac-(1'S,2R)- tert-butyl 2-(4'-bromo-1'-hydroxybutyl)-5-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate, C13H20BrNO4, (III), are 5-hydroxyalkyl derivatives of tert-butyl 2-oxo-2,5-dihydropyrrole-1-carboxylate. In all three compounds, the tert-butoxycarbonyl (Boc) unit is orientated in the same manner with respect to the mean plane through the 2-oxo-2,5-dihydro-1H-pyrrole ring. The hydroxyl substituent at one of the newly created chiral centres, which have relative R,R stereochemistry, is trans with respect to the oxo group of the pyrrole ring in (I), synthesized using acetaldehyde. When a larger aldehyde was used, as in compounds (II) and (III), the hydroxyl substituent was found to be cis with respect to the oxo group of the pyrrole ring. Here, the relative stereochemistry of the newly created chiral centres is R,S. In compound (I), O-H···O hydrogen bonding leads to an interesting hexagonal arrangement of symmetry-related molecules. In (II) and (III), the hydroxyl groups are involved in bifurcated O-H···O hydrogen bonds, and centrosymmetric hydrogen-bonded dimers are formed. The Mukaiyama crossed-aldol-type reaction was successful when using the 2-nitrophenyl-substituted hydroxypyrrole, or the unsubstituted hydroxypyrrole, and boron trifluoride diethyl ether as catalyst. The synthetic procedure leads to a syn configuration of the two newly created chiral centres in all three compounds.