Crystal structures of two 1,2,3,4-tetra-hydro-naphthalenes obtained during efforts towards the total synthesis of elisabethin A.

The two substituted 1,2,3,4-tetra-hydro-naphthalenes, methyl (R)-3-{(1R,4S)-6-meth-oxy-4,7-dimethyl-5,8-bis-[(triiso-propyl-sil-yl)-oxy]-1,2,3,4-tetra-hydro-naph-th-al-en-1-yl}butano-ate, C36H66O5Si2, (2), and methyl (E)-3-{(1R,4S)-8-hy-droxy-6-meth-oxy-4,7-dimethyl-5-[(triiso-propyl-sil-yl)-oxy]-1,2,3,4-tetra-hydro-naphthalen-1-yl}acrylate, C26H42O5Si, (8), crystallize in the Sohncke space groups P212121 and P21, respectively, with the absolute structure determined on the basis of anomalous dispersion effects. The configurations of the stereo centres in the 1,2,3,4-tetra-hydro-naphthalene moiety of (2) and (8) are the same, and the conformation of the non-aromatic part of the ring system is nearly identical. In the crystal of (2), weak non-classical C-H⋯O inter-actions consolidate the packing, whereas in (8), inter-molecular O-H⋯O hydrogen-bonding inter-actions of medium-to-weak strength direct the mol-ecules into Z-shaped strands extending parallel to [010].

Introducing a new 7-ring fused diindenone-dithieno[3,2-b:2',3'-d]thiophene unit as a promising component for organic semiconductor materials.

A novel π-conjugated molecule, EtH-T-DI-DTT is reported, which is fused, rigid, and planar, featuring the electron-rich dithieno[3,2-b:2',3'-d]thiophene (DTT) unit in the core of the structure. Adjacent to the electron-donating DTT core, there are indenone units with electron-withdrawing keto groups. To enable solubility in common organic solvents, the fused system is flanked by ethylhexylthiophene groups. The material is a dark, amorphous solid with an onset of absorption at 638 nm in CH2Cl2 solution, which corresponds to an optical gap of 1.94 eV. In films, the absorption onset wavelength is at 701 nm, which corresponds to 1.77 eV. An ionisation energy of 5.5 eV and an electron affinity of 3.3 eV were estimated by cyclic voltammetry measurements. We have applied this new molecule in organic field effect transistors. The material exhibited a p-type mobility up to 1.33 × 10-4 cm2 V-1 s-1.

Colletotrichalactones A-Ca, unusual 5/6/10-fused tricyclic polyketides produced by an endophytic fungus, Colletotrichum sp. JS-0361.

Three unusual polyketides with a 5/6/10-fused ring system, named colletotrichalactones A-Ca (1-3a), were isolated from cultures of the endophytic fungus, Colletotrichum sp. JS-0361, which was isolated from a leaf of Morus alba. Their structures, including their absolute stereochemistries, were completely established using extensive spectroscopic methods together with a chemical reaction utilizing competing enantioselective acylation coupled with LC/MS. Compounds possessing this ring skeleton were previously reported in three studies. Our rigorous chemical investigation revealed the complete configuration of this skeleton, which agreed with the results for glabramycin B with this ring skeleton established by computational chemistry and enantioselective synthesis in previous reports. 1 and 2 had unstable aldehyde groups that were easily converted to acetal groups in the presence of solvents. Meanwhile, compound 3a, with terminal acetal functionality, was deduced to be an artefact originating from compound 3 with a terminal aldehyde group. Compounds 1 and 3a displayed moderate-to-potent cytotoxic activities against MCF7 cells with IC50s of 35.06 and 25.20 µM, respectively.

One-Pot Cascade Transformation of Glucal into Structurally Diverse Drug-Like Scaffolds.

A diversity-oriented synthesis strategy to produce three types of structurally drug-like N-heterocyclic-fused rings has been developed from abundant biomass-derived d-glucal, aniline and water in a stereoselective manner. The overall transformation which entails a cascade of Ferrier reaction and 4π conrotatory imino-Nazarov cyclization was performed in one-pot allowing convenient preparation of scaffolds of high molecular complexity from relatively simple starting materials. While indoline-fused products were readily accessible using ortho-unsubstituted secondary anilines as substrates, reactions with ortho-hydroxyl-anilines furnished fused 1,4-benzoxazines instead. In both cases, InBr3 acted as the Lewis acid catalyst. By altering InBr3 to Ln(OTf)3 , the indoline-fused products could be further converted into tetrahydroquinoline-fused cyclopentenones via ensuing retro-ene rearrangement.

Synthesis of π-Conjugated Benzocyclotrimers.

Polycyclic aromatic hydrocarbons (PAHs), especially three branchphene benzocyclotrimers represent a series of molecules with intriguing physical and chemical properties. Benzocyclotrimers are also important precursors to construct fullerenes and graphenes. In this article, we review the recent progress in the preparation methods of π-conjugated benzocyclotrimers. In particular, cyclotrimerization reactions to construct varying shaped and edged benzocyclotrimers are illustrated. Various typical characterization methods for these materials, such as variable-temperature 1 H-NMR, single crystal X-ray analysis, density functional theory (DFT) calculations and atomic force microscope (AFM) measurements are included for discussion.

Diversity-oriented synthesis of bicyclic fragments containing privileged azines.

An innovative and efficient reagent- and scaffold-based diversity oriented synthesis (DOS) of a fragment set was developed for fragment-based drug discovery (FBDD) programs. Twelve diverse, functionalized and bicyclic scaffolds were rapidly accessed by adopting a convenient synthetic toolkit around three privileged azine cores in order to effectively modulate biomolecules. These structures are characterized by both key motifs for interacting with diverse biological targets via hydrogen bonds and useful points of growth for subsequent fragment optimization.

Microwave Assisted Synthesis of Biorelevant Benzazoles.

The benzazole scaffolds are present in various therapeutic agents and have been recognized as the essential pharmacophore for diverse biological activities. These have generated interest and necessity to develop efficient synthetic methods of these privileged classes of compounds to generate new therapeutic leads for various diseases. The biological activities of the benzazoles and efforts towards their synthesis have been summarized in a few review articles. In view of these, the aim of this review is to provide an account of the developments that have taken place in the synthesis of biorelevant benzazoles under microwave irradiation as the application of microwave heating has long been recognized as a green chemistry tool for speedy generation of synthetic targets. Attention has been focused to those literature reports wherein the use of microwave irradiation is the key step in the formation of the heterocyclic ring system or in functionalization of the benzazole ring system to generate the essential pharmacophoric feature. The convenient and economic way to synthesize these privileged class of heterocycles through the use of microwave irradiation that would be beneficial for the drug discovery scientist to synthesize biologically active benzazoles and provide access to wide range of reactions for the synthesis of benzazoles constitute the theme of this review. Examples have been drawn wherein the use of microwave heating offers distinct advantage in terms of improved product yields and reduction of reaction time as compared to those observed for the synthesis under conventional heating.

Total Syntheses of (+)-Grandilodine†C and (+)-Lapidilectine†B and Determination of their Absolute Stereochemistry.

Enantioselective total syntheses of the Kopsia alkaloids (+)-grandilodine C and (+)-lapidilectine B were accomplished. A key intermediate, spirodiketone, was synthesized in 3 steps and converted into the chiral enone by enantioselective deprotonation followed by oxidation with up to 76 % ee. Lactone formation was achieved through stereoselective vinylation followed by allylation and ozonolysis. The total synthesis of (+)-grandilodine C was achieved by palladium-catalyzed intramolecular allylic amination and ring-closing metathesis to give 8- and 5-membered heterocycles, respectively. Selective reduction of a lactam carbonyl gave (+)-lapidilectine B. The absolute stereochemistry of both natural products was thereby confirmed. These syntheses enable the scalable preparation of the above alkaloids for biological studies.

Crystal structure of 6,6,12,12-tetra-chloro-tri-cyclo-[8.2.0.0(4,7)]dodecane-5,11-dione.

The asymmetric unit of the title compound, C12H12Cl4O2, contains two crystallographically independent mol-ecules with almost identical conformations (r.m.s. overlay fit for the non-hydrogen atoms = 0.059 Å). In each mol-ecule, the central eight-membered ring has a distorted boat configuration, and two non-planar four-membered rings are fused on either side of the eight-membered ring. A weak C-H⋯O hydrogen bond links the two independent mol-ecules. In the crystal, weak C-H⋯O hydrogen bonds link the mol-ecules into a two-dimensional network parallel to (001).

Crystal structure of 10-[(3-oxo-3H-benzo[f]chromen-1-yl)meth-yl]-2-tri-fluoro-methyl-9a,10-di-hydro-benz[4,5]imidazo[1,2-a]pyrimidin-4(5aH)-one.

In the title compound, C25H14F3N3O3, the dihedral angle between the planes of the benz[4,5]imidazo[1,2-a]pyrimidine unit (r.m.s. deviation = 0.035 Å) and the benzochromene ring system (r.m.s. deviation = 0.106 Å) is 72.82 (5)°. In the crystal, mol-ecules are linked by C-H⋯O inter-actions, generating [010] C(9) chains. A weak aromatic π-π stacking inter-action [centroid-centroid separation = 3.5376 (15) Å] is also observed.

Construction of a hemifullerene skeleton: a regioselective intramolecular oxidative cyclization.

A two-step synthesis of a strained π bowl, with hemifullerene skeleton from sumanene, was achieved in a high yield. The first step is a base-promoted condensation reaction with a benzophenone compound, bis(3,5-dimethylphenyl)methanone. The second step is the regioselective intramolecular oxidative cyclization, which is a key reaction for the hemifullerene skeleton synthesis. This regioselective cyclization is likely to be under thermodynamic control. This strategy will allow facile synthesis of various highly strained π bowls.