Self‐aggregation of Synthetic Zinc Chlorophyll Derivatives Possessing 31‐Hydroxy or Methoxy Group and 131‐Mono‐ or Dicyanomethylene Moiety in Nonpolar Organic Solvents as Models of Chlorosomal Bacteriochlorophyll‐d Aggregates

Methyl 13¹‐(di)cyanomethylene‐pyropheophorbides were synthesized by Knoevenagel reactions of the corresponding 13¹‐oxo‐chlorins prepared from modifying chlorophyll‐a with malononitrile or cyanoacetic acid. Alternatively, methyl 13¹‐cyanomethylene‐pyropheophorbides were produced by Wittig reactions of 13¹‐oxo‐chlorins with Ph₃P=CHCN. Self‐aggregation of zinc complexes of the semi‐synthetic chlorophyll derivatives possessing a hydroxy or methoxy group at the 3¹‐position was examined in 1%(v/v) tetrahydrofuran or dichloromethane and hexane by electronic absorption and circular dichroism spectroscopy. Although intermolecular hydrogen‐bonding between the 3¹‐hydroxy and 13¹‐oxo groups of bacteriochlorophylls‐c/d/e/f was essential for their self‐aggregation in natural light‐harvesting antenna systems (=chlorosomes), zinc 3¹‐hydroxy‐13¹‐di/monocyanomethylene‐chlorins self‐aggregated in the less/lesser polar organic solvents to form chlorosome‐like large oligomers in spite of lacking the 13¹‐oxo moiety as the hydrogen‐bonding acceptor. Zinc 3¹‐methoxy‐13¹‐dicyanomethylene‐chlorin gave similar self‐aggregates regardless of lack of both the 3¹‐hydroxy and 13¹‐oxo groups. The present self‐aggregation was ascribable to stronger coordination of the 3¹‐oxygen atom to the central zinc than the conventional systems, where the electron‐withdrawing cyano group(s) increased the coordinative ability of the central zinc through the chlorin π‐system.     

2‐(4‐Bromophenyl)‐1,2‐dihydropyrimido[1,2‐a]benzimidazol‐4(3H)‐one and 4‐(4‐methylphenyl)‐3,4‐dihydropyrimido[1,2‐a]benzimidazol‐2(1H)‐one form hydrogen‐bonded base‐paired dimers

The title compounds, 2‐(4‐bromo­phenyl)‐1,2‐di­hydro­pyrimido­[1,2‐a]­benzimidazol‐4‐(3H)‐one, C₁₆H₁₂Br­N₃O, (IVa), and 4‐(4‐methylphenyl)‐3,4‐dihydropyrimido[1,2‐a]benzimidazol‐2‐(1H)‐one, C₁₇H₁₅N₃O, (Vb), both form R(8) centrosymmetric dimers via N—H?N hydrogen bonds. The N?N distance is 2.943 (3) Å for (IVa) and 2.8481 (16) Å for (Vb), with the corresponding N—H?N angles being 129 and 167°, respectively. However, in other respects, the supra­molecular structures of the two compounds differ. Both compounds contain different C—H?π interactions, in which the C—H?π(centroid) distances are 2.59 and 2.47 Å for (IVa) and (Vb), respectively (the latter being a short distance), with C—H?π(centroid) angles of 158 and 159°, respectively. The supramolecular structures also differ, with a short Br?O distance of 3.117 (2) Å in bromo derivative (IVa), and a C—H?O interaction with a C?O distance of 3.2561 (19) Å and a C—H?O angle of 127° in tolyl system (Vb). The di­hydro­pyrimido part of (Vb) is disordered, with a ratio of the major and minor components of 0.9:0.1. The disorder consists of two non‐interchangeable envelope conformers, each with an equatorial tolyl group and an axial methine H atom.     

Syntheses of Chalcone‐Type Chlorophyll Derivatives Possessing a Bacteriochlorin,Chlorin or Porphyrin π‐System and Their Optical Properties

C3‐(Trans‐2‐arylethenyl)carbonylated chlorophyll derivatives possessing a bacteriochlorin or chlorin π‐system were synthesized by cross‐aldol (Claisen–Schmidt) condensation of methyl pyrobacteriopheophorbide‐a or 3‐acetyl‐3‐devinyl‐pyropheophorbide‐a bearing the C3‐acetyl group with p‐(un)substituted benzaldehydes under basic conditions. The corresponding porphyrin‐type chlorophyll derivatives were prepared by the oxidation (17,18‐didehydrogenation) of the chlorin‐type. Their Qy absorption and fluorescence emission maxima in dichloromethane correlated well with Hammett substituent constants of the p‐substituents. Several electron‐withdrawing p‐substituents suppressed the emission due to photoinduced electron transfer quenching in a molecule. The substitution sensitivities for their maxima and fluorescence quantum yields decreased in the order of bacteriochlorin‐, chlorin‐ and porphyrin‐type derivatives.     

Reactions between arylhydrazinium chlorides and 2‐chloroquinoline‐3‐carbaldehydes: molecular and supramolecular structures of a hydrazone,a 4,9‐dihydro‐1H‐pyrazolo[3,4‐b]quinoline and two 1H‐pyrazolo[3,4‐b]quinolines

Hydrazone derivatives exhibit a wide range of biological activities, while pyrazolo[3,4‐b]quinoline derivatives, on the other hand, exhibit both antimicrobial and antiviral activity, so that all new derivatives in these chemical classes are potentially of value. Dry grinding of a mixture of 2‐chloroquinoline‐3‐carbaldehyde and 4‐methylphenylhydrazinium chloride gives (E)‐1‐[(2‐chloroquinolin‐3‐yl)methylidene]‐2‐(4‐methylphenyl)hydrazine, C₁₇H₁₄ClN₃, (I), while the same regents in methanol in the presence of sodium cyanoborohydride give 1‐(4‐methylphenyl)‐4,9‐dihydro‐1H‐pyrazolo[3,4‐b]quinoline, C₁₇H₁₅N₃, (II). The reactions between phenylhydrazinium chloride and either 2‐chloroquinoline‐3‐carbaldehyde or 2‐chloro‐6‐methylquinoline‐3‐carbaldehyde give, respectively, 1‐phenyl‐1H‐pyrazolo[3,4‐b]quinoline, C₁₆H₁₁N₃, (III), which crystallizes in the space group Pbcn as a nonmerohedral twin having Z′ = 3, or 6‐methyl‐1‐phenyl‐1H‐pyrazolo[3,4‐b]quinoline, C₁₇H₁₃N₃, (IV), which crystallizes in the space group R. The molecules of compound (I) are linked into sheets by a combination of N—H…N and C—H…π(arene) hydrogen bonds, and the molecules of compound (II) are linked by a combination of N—H…N and C—H…π(arene) hydrogen bonds to form a chain of rings. In the structure of compound (III), one of the three independent molecules forms chains generated by C—H…π(arene) hydrogen bonds, with a second type of molecule linked to the chains by a second C—H…π(arene) hydrogen bond and the third type of molecule linked to the chain by multiple π–π stacking interactions. A single C—H…π(arene) hydrogen bond links the molecules of compound (IV) into cyclic centrosymmetric hexamers having (S₆) symmetry, which are themselves linked into a three‐dimensional array by π–π stacking interactions.     

ACE applied to the quantitative characterization of benzo‐18‐crown‐6‐ether binding with alkali metal ions in a methanol–water solvent system

ACE was applied to the quantitative evaluation of noncovalent binding interactions between benzo‐18‐crown‐6‐ether (B18C6) and several alkali metal ions, Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺, in a mixed binary solvent system, methanol–water (50/50 v/v). The apparent binding (stability) constants (K_b) of B18C6–alkali metal ion complexes in the hydro‐organic medium above were determined from the dependence of the effective electrophoretic mobility of B18C6 on the concentration of alkali metal ions in the BGE using a nonlinear regression analysis. Before regression analysis, the mobilities measured by ACE at ambient temperature and variable ionic strength of the BGE were corrected by a new procedure to the reference temperature, 25°C, and the constant ionic strength, 10 mM . In the 50% v/v methanol–water solvent system, like in pure methanol, B18C6 formed the strongest complex with potassium ion (log K_b=2.89±0.17), the weakest complex with cesium ion (log K_b=2.04±0.20), and no complexation was observed between B18C6 and the lithium ion. In the mixed methanol–water solvent system, the binding constants of the complexes above were found to be about two orders lower than in methanol and about one order higher than in water.     

Diastereoisomeric forms of 11‐ethyl‐6,11‐dihydro‐5H‐dibenzo[b,e]azepine‐6‐carboxamide: syntheses and the molecular and supramolecular structure of the minor form (6RS,11RS)‐11‐ethyl‐6,11‐dihydro‐5H‐dibenzo[b,e]azepine‐6‐carboxamide

Compounds containing the tricyclic dibenzo[b,e]azepine system have potential activity in the treatment of a number of diseases. Continuing with our studies on the synthesis of new small and potentially bioactive molecules, a synthetic route, involving acid‐catalysed intramolecular Friedel–Crafts cyclization, to the readily separable diastereoisomers of 11‐ethyl‐6,11‐dihydro‐5H‐dibenzo[b,e]azepine‐6‐carboxamide, a potentially useful precursor in the synthesis of analogues of some anti‐allergenic, antidepressant and antihistaminic drugs currently in use, has been developed starting from 2‐allylphenylamine and methyl 2‐bromo‐2‐phenylacetate and proceeding via racemic methyl 2‐[(2‐allylphenyl)amino]‐2‐phenylacetate (A) and racemic 2‐[(2‐allylphenyl)amino]‐2‐phenylacetamide (B), to give the two diastereoisomers (I) and (II), C₁₇H₁₈N₂O. Isomers (I) and (II), and their precursors (A) and (B), have all been fully characterized spectroscopically. Structure analysis of the minor isomer (I) shows that it has the (6RS,11RS) configuration, and that the azepine ring adopts a conformation intermediate between the boat and twist‐boat forms, with the carboxamide and ethyl substituents both occupying quasi‐equatorial sites. The molecules of (I) are linked by a combination of N—H…O, N—H…π(arene) and C—H…π(arene) hydrogen bonds to form complex sheets. Comparisons are made with the structures of some related compounds.     

Synthesis,self‐assembly,and formation of photo‐crosslinking‐stabilized fluorescent micelles covalently containing zinc(II)‐bis(8‐hydroxyquinoline) for ABC triblock copolymer bearing cinnamoyl and 8‐hydroxyquinoline side groups

Triblock copolymers (MPEG‐b‐PCEMA‐b‐PHQHEMA) bearing cinnamoyl and 8‐hydroxyquinoline side groups with different block length are synthesized by a two‐step reversible addition fragmentation chain transfer polymerization of cinnamoyl ethyl methacrylate (CEMA) and 2‐((8‐hydroxyquinolin‐5‐yl)methoxy)ethyl methacrylate (HQHEMA), respectively. The self‐assembly of MPEG‐b‐PCEMA‐b‐PHQHEMA in mixture of THF and ethanol is investigated by varying the ratio of THF and ethanol. Spheric micelles with diameter of 63.7 nm and polydispersity of 0.128 are obtained for MPEG₁₁₃‐b‐PCEMA₁₅‐b‐PHQHEMA₁₇ in THF/ethanol with a volume ratio (v/v) of 5/5. The PCEMA inner shell of the resulted micelles is photo‐crosslinked under UV radiation to give stabilized micelles. The complex reaction of the stabilized micelles with Zn(II) is investigated under different conditions to give zinc(II)‐bis(8‐hydroxyquinoline)(Znq₂)‐containing micelles. When the complex reaction is carried out in THF/ethanol (v/v = 5/5) or THF/toluene (v/v = 6/4) with zinc acetate, fluorescent Znq₂‐containing micelles are obtained without obvious change in diameters and morphologies. The fluorescent micelles exhibit green emission with λ_max at 520 nm. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1056–1064     

2‐[4‐Phenyl‐5‐(2‐pyridyl)‐4H‐1,2,4‐triazol‐3‐yl]nicotinic acid: a case of solvent‐dependent polymorphism

The title compound, C₁₉H₁₃N₅O₂, crystallizes in two monoclinic forms depending on the solvent used. From methanol or acetone, a yellow form [(Ia), m.p. 533 K] in the space group P2₁ is obtained, while with ethanol as the solvent, an orange form [(Ib), m.p. 541 K] in the space group Cc results. The conformers observed in the two polymorphs differ primarily in the relative orientation of pyridine/phenyl and triazole rings. Molecules of both polymorphs form chains through carboxyl O—H...N hydrogen bonding; however, in each crystal structure, a different group acts as acceptor, viz. a triazole and a pyridyl N atom for (Ia) and (Ib), respectively. This is the first case of polymorphism observed for crystals of a 3,4,5‐trisubstituted 1,2,4‐triazole derivative.     

Three closely related thienyl‐substituted 1,4‐epoxynaphtho[1,2‐b]azepines: hydrogen‐bonded assembly in one,two and three dimensions

(2R,4S)‐2‐(3‐Methylthiophen‐2‐yl)‐2,3,4,5‐tetrahydro‐1,4‐epoxynaphtho[1,2‐b]azepine, C₁₉H₁₇NOS, (I), crystallizes with a single enantiomer in each crystal, whereas its geometrical isomer (2RS,4SR)‐2‐(5‐methylthiophen‐2‐yl)‐2,3,4,5‐tetrahydro‐1,4‐epoxy‐naphtho[1,2‐b]azepine, (II), and (2RS,4SR)‐2‐(5‐bromothiophen‐2‐yl)‐2,3,4,5‐tetrahydro‐1,4‐epoxynaphtho[1,2‐b]azepine, C₁₈H₁₄BrNOS, (III), both crystallize as racemic mixtures. A combination of one C—H...O hydrogen bond and two C—H...π(arene) hydrogen bonds links the molecules of (I) into a three‐dimensional framework; the molecules of (II) are linked into a C(4)C(4)[R₂²(7)] chain of rings by a combination of C—H...N and C—H...O hydrogen bonds; and in (III), where Z′ = 2, a combination of four C—H...π(arene) hydrogen bonds and two C—H...π(thienyl) hydrogen bonds links the molecules into complex sheets. Comparisons are made with the assembly patterns in some aryl‐substituted 1,4‐epoxynaphtho[1,2‐b]azepines.     

Effects of Substituents on Synthetic Analogs of Chlorophylls. Part 4: How Formyl Group Location Dictates the Spectral Properties of Chlorophylls b,d and f

Photosynthetic organisms are adapted to light characteristics in their habitat in part via the spectral characteristics of the associated chlorophyll pigments, which differ in the position of a formyl group around the chlorin macrocycle (chlorophylls b, d, f) or no formyl group (chlorophyll a). To probe the origin of this spectral tuning, the photophysical and electronic structural properties of a new set of synthetic chlorins are reported. The zinc and free base chlorins have a formyl group at either the 2‐ or 3‐position. The four compounds have fluorescence yields in the range 0.19–0.28 and singlet excited‐state lifetimes of ca 4 ns for zinc chelates and ca 8 ns for the free base forms. The photophysical properties of the 2‐ and 3‐formyl zinc chlorins are similar to those observed previously for 13‐formyl or 3,13‐diformyl chlorins, but differ markedly from those for 7‐formyl analogs. Molecular‐orbital characteristics obtained from density functional theory (DFT) calculations were used as input to spectral simulations employing the four‐orbital model. The analysis has uncovered the key changes in electronic structure engendered by the presence/location of a formyl group at various macrocycle positions, which is relevant to understanding the distinct spectral properties of the natural chlorophylls a, b, d and f.     

Mechanochromism,Twisted/Folded Structure Determination,and Derivatization of (N‐Phenylfluorenylidene)acridane

(N‐Phenylfluorenylidene)acridane (Ph‐FA) compounds with electron‐withdrawing and ‐donating substituents (H, MeO, Ph, NO₂, Br, F) at the para position of the phenyl group were successfully synthesized by Barton–Kellogg reactions of N‐aryl thioacridones and diazofluorene. By using the substituent on the nitrogen atom to alter the electronic properties, both the folded and twisted conformers of p‐NO₂‐C₆H₄‐FA could be crystallographically characterized, which enabled the charge transfer from the electron‐donating acridane moiety to the electron‐accepting fluorenylidene moiety to be understood. Ground‐state mechanochromism, thermochromism, vapochromism, and proton‐induced chromism were demonstrated between the folded and twisted conformations of the conformers. Protonation and chemical oxidation of Ph‐FA gave two stable acridinium compounds, namely, the fluorenylacridinium and acridinium radical cations. The present study will contribute to the development of functional dyes and organic semiconductors.     

Kinetics of the Reaction of 2‐Chloro‐3,5‐dinitrobenzotriflouride with Aniline in Toluene and Methanol‐Toluene Mixed Solvents

Kinetics of the reaction of 2‐chloro‐3,5‐dinitrobenzotriflouride with aniline were studied in toluene, methanol‐toluene binary solvents, benzene and chloroform. The reaction in toluene exhibits third‐order kinetics consistent with aggregates of aniline. Thermodynamic parameters (H^#, (S^# and (G^#are calculated and discussed for the reaction of 2‐chloro‐3,5‐dinitrobenzotriflouride with aniline in methanol‐toluene. Molecular complexes between aniline and the substrate are rejected spectrophotometricaly. The mechanism is studied and compared with the reaction in presence of pyridine. It shows an amine dependence and formation of homo and/or hetero mixed aggregates between aniline and pyridine i.e. dimer mechanism.     

Mechanochromism,Twisted/Folded Structure Determination,and Derivatization of (N‐Phenylfluorenylidene)acridane

(N‐Phenylfluorenylidene)acridane (Ph‐FA) compounds with electron‐withdrawing and ‐donating substituents (H, MeO, Ph, NO₂, Br, F) at the para position of the phenyl group were successfully synthesized by Barton–Kellogg reactions of N‐aryl thioacridones and diazofluorene. By using the substituent on the nitrogen atom to alter the electronic properties, both the folded and twisted conformers of p‐NO₂‐C₆H₄‐FA could be crystallographically characterized, which enabled the charge transfer from the electron‐donating acridane moiety to the electron‐accepting fluorenylidene moiety to be understood. Ground‐state mechanochromism, thermochromism, vapochromism, and proton‐induced chromism were demonstrated between the folded and twisted conformations of the conformers. Protonation and chemical oxidation of Ph‐FA gave two stable acridinium compounds, namely, the fluorenylacridinium and acridinium radical cations. The present study will contribute to the development of functional dyes and organic semiconductors.     

Chlorin–Bacteriochlorin Energy‐transfer Dyads as Prototypes for Near‐infrared Molecular Imaging Probes: Controlling Charge‐transfer and Fluorescence Properties in Polar Media

The photophysical properties of two energy‐transfer dyads that are potential candidates for near‐infrared (NIR) imaging probes are investigated as a function of solvent polarity. The dyads ( FbC‐FbB and ZnC‐FbB ) contain either a free base (Fb) or zinc (Zn) chlorin (C) as the energy donor and a free base bacteriochlorin (B) as the energy acceptor. The dyads were studied in toluene, chlorobenzene, 1,2‐dichlorobenzene, acetone, acetonitrile and dimethylsulfoxide (DMSO). In both dyads, energy transfer from the chlorin to bacteriochlorin occurs with a rate constant of ～(5–10 ps)^?1 and a yield of >99% in nonpolar and polar media. In toluene, the fluorescence yields (Φ _f = 0.19) and singlet excited‐state lifetimes (τ～5.5 ns) are comparable to those of the benchmark bacteriochlorin. The fluorescence yield and excited‐state lifetime decrease as the solvent polarity increases, with quenching by intramolecular electron (or hole) transfer being greater for FbC‐FbB than for ZnC‐FbB in a given solvent. For example, the Φ _f and τ values for FbC‐FbB in acetone are 0.055 and 1.5 ns and in DMSO are 0.019 and 0.28 ns, whereas those for ZnC‐FbB in acetone are 0.12 and 4.5 ns and in DMSO are 0.072 and 2.4 ns. The difference in fluorescence properties of the two dyads in a given polar solvent is due to the relative energies of the lowest energy charge‐transfer states, as assessed by ground‐state redox potentials and supported by molecular‐orbital energies derived from density functional theory calculations. Controlling the extent of excited‐state quenching in polar media will allow the favorable photophysical properties of the chlorin–bacteriochlorin dyads to be exploited in vivo. These properties include very large Stokes shifts (85 nm for FbC‐FbB , 110 nm for ZnC‐FbB ) between the red‐region absorption of the chlorin and the NIR fluorescence of the bacteriochlorin (λ _f = 760 nm), long bacteriochlorin excited‐state lifetime (～5.5 ns), and narrow (≤20 nm) absorption and fluorescence bands. The latter will facilitate selective excitation/detection and multiprobe applications using both intensity‐ and lifetime‐imaging techniques.     

(9E)‐9‐Benzylidene‐3‐methyl‐2‐methylsulfanyl‐5‐phenyl‐5,6,7,8,9,10‐hexahydropyrimido[4,5‐b]quinolin‐4(3H)‐one: polarized molecules within hydrogen‐bonded bilayers

The molecules of the title compound, C₂₆H₂₅N₃OS, which was prepared by means of an acid‐catalysed cyclocondensation reaction between a 6‐aminopyrimidinone and 2,6‐dibenzylidenecyclohexanone, exhibit a polarized electronic structure, namely (9E)‐9‐benzylidene‐3‐methyl‐2‐methylsulfanyl‐5‐phenyl‐3,5,6,7,8,9‐hexahydropyrimido[4,5‐b]quinolin‐10‐ium‐4‐olate, involving charge separation in the vinylogous amide portion. Four hydrogen bonds, two each of the C—H...O and C—H...π(arene) types, link the molecules into bilayers comprising inversion‐related pairs of sheets, each containing a single type of R₄³(36) ring.     

Hydrogen‐bonded sheet structures in methyl 4‐(4‐chloroanilino)‐3‐nitrobenzoate and methyl 1‐benzyl‐2‐(4‐chlorophenyl)‐1H‐benzimidazole‐5‐carboxylate

In methyl 4‐(4‐chloroanilino)‐3‐nitrobenzoate, C₁₄H₁₁ClN₂O₄, (I), there is an intramolecular N—H...O hydrogen bond and the intramolecular distances provide evidence for electronic polarization of the o‐quinonoid type. The molecules are linked into sheets built from N—H...O, C—H...O and C—H...π(arene) hydrogen bonds, together with an aromatic π–π stacking interaction. The molecules of methyl 1‐benzyl‐2‐(4‐chlorophenyl)‐1H‐benzimidazole‐5‐carboxylate, C₂₂H₁₇ClN₂O₂, (II), are also linked into sheets, this time by a combination of C—H...π(arene) hydrogen bonds and aromatic π–π stacking interactions.     

Supramolecular framework in catena‐poly[[(nitrato‐κO)silver(I)]‐μ‐(R,S)‐2‐(pyridin‐4‐ylsulfinyl)pyrimidine‐κ3N,O:N′]

In the title complex, [Ag(NO₃)(C₉H₇N₃OS)]_n, η¹:η¹:η¹:μ₂‐bridging 2‐(pyridin‐4‐ylsulfinyl)pyrimidine (pypmSO) ligands with opposite chiralities are alternately arranged to link the Ag^I cations through two N atoms and one sulfinyl O atom of each ligand, leading to an extended zigzag coordination chain structure along the [01] direction. An FT–IR spectroscopic study shows a decreased stretching frequency for the η¹‐O‐bonded S=O group compared with that of the free ligand. The parallel chains are arranged and interconnected via O(S=O)...π(pyridine/pyrimidine) and C—H(pyridine)...O(NO₃⁻) interactions to furnish a layer almost parallel to the ac plane. Along the b axis, the layers are stacked and stabilized through anion(NO₃⁻)...π(pyrimidine) interactions to form a three‐dimensional supramolecular framework. The ligand behaviour of the new diheterocyclic sulfoxide and the unconventional O(S=O)...π(pyridine/pyrimidine) and anion(NO₃⁻)...π(pyrimidine) interactions in the supramolecular assembly of the title complex are presented.     

Synthesis and Analysis of the Conformational Preferences of 5‐Aminomethyloxazolidine‐2,4‐dione Scaffolds: First Examples of β2‐ and β2, 2‐Homo‐Freidinger Lactam Analogues

Constrained peptidomimetic scaffolds are of considerable interest for the design of therapeutically useful analogues of bioactive peptides. We present the single‐step cyclization of (S)‐ or (R)‐α‐hydroxy‐β²‐ or α‐substituted‐α‐hydroxy‐β^{2, 2}‐amino acids already incorporated within oligopeptides to 5‐aminomethyl‐oxazolidine‐2,4‐dione (Amo) rings. These scaffolds can be regarded as unprecedented β²‐ or β^{2, 2}‐homo‐Freidinger lactam analogues, and can be equipped with a proteinogenic side chain at each residue. In a biomimetic environment, Amo rings act as inducers of extended, semi‐bent or folded geometries, depending on the relative stereochemistry and the presence of α‐substituents.     

Five closely related 4‐chloro‐6,11‐dihydro‐5H‐benzo[b]pyrimido[5,4‐f]azepines: similar molecular structures but different supramolecular assemblies

Dibenz[b,f]azepine (DBA) is a privileged 6‐7‐6 tricyclic ring system of importance in both organic and medicinal chemistry. Benzo[b]pyrimido[5,4‐f]azepines (BPAs), which also contain a privileged 6‐7‐6 ring system, are less well investigated, probably because of a lack of straightforward and versatile methods for their synthesis. A simple and versatile synthetic approach to BPAs based on intramolecular Friedel–Crafts alkylation has been developed. A group of closely‐related benzo[b]pyrimido[5,4‐f]azepine derivatives, namely (6RS)‐4‐chloro‐6,11‐dimethyl‐6,11‐dihydro‐5H‐benzo[b]pyrimido[5,4‐f]azepine, C₁₄H₁₄ClN₃, (I), (6RS)‐4‐chloro‐8‐hydroxy‐6,11‐dimethyl‐6,11‐dihydro‐5H‐benzo[b]pyrimido[5,4‐f]azepine, C₁₄H₁₄ClN₃O, (II), (6RS)‐4‐<!?tlsb=‐0.14pt>chloro‐8‐methoxy‐6,11‐dimethyl‐6,11‐dihydro‐5H‐benzo[b]pyrimido[5,4‐f]azepine, C₁₅H₁₆ClN₃O, (III), and (6RS)‐4‐chloro‐8‐methoxy‐6,11‐dimethyl‐2‐phenyl‐6,11‐dihydro‐5H‐benzo[b]pyrimido[5,4‐f]azepine, C₂₁H₂₀ClN₃O, (IV), has been prepared and their structures compared with the recently published structure [Acosta‐Quintero et al. (2015). Eur. J. Org. Chem. pp. 5360–5369] of (6RS)‐4‐chloro‐2,6,8,11‐tetramethyl‐6,11‐dihydro‐5H‐benzo[b]pyrimido[5,4‐f]azepine, (V). All five compounds crystallize as racemic mixtures and they have very similar molecular conformations, with the azepine ring adopting a boat‐type conformation in each case, although the orientation of the methoxy substituent in each of (III) and (IV) is different. The supramolecular assemblies in (II) and (IV) depend upon hydrogen bonds of the O—H...N and C—H...π(arene) types, respectively, those in (I) and (V) depend upon π–π stacking interactions involving pairs of pyrimidine rings, and that in (III) depends upon a π–π stacking interaction involving pairs of phenyl rings. Short C—Cl...π(pyrimidine) contacts are present in (I), (II) and (IV) but not in (III) or (V).     

1,4‐Phenylenebis(methylene) bis(9H‐carbazole‐9‐carbodithioate)

The molecules of the title compound, C₃₄H₂₄N₂S₄, lie across centres of inversion in the space group P2₁/n. The spacer unit linking the benzene rings and carbazole units is effectively planar, while the carbazole unit itself is slightly folded. Molecules are linked into sheets by a single C—H...π(arene) hydrogen bond and the hydrogen‐bonded sheets are themselves linked into a three‐dimensional framework structure by a single π–π stacking interaction.