Convergent Total Syntheses of (−)‐Rubriflordilactone B and (−)‐pseudo‐Rubriflordilactone B

A highly convergent strategy for the synthesis of the natural product (?)‐rubriflordilactone B, and the proposed structure of (?)‐pseudo‐rubriflordilactone B, is described. Late stage coupling of diynes containing the respective natural product FG rings with a common AB ring aldehyde precedes rhodium‐catalyzed [2+2+2] alkyne cyclotrimerization to form the natural product skeleton, with the syntheses completed in just one further operation. This work resolves the uncertainty surrounding the identity of pseudo‐rubriflordilactone B and provides a robust platform for further synthetic and biological investigations.     

Absolute Configuration of the Phenylpropanoid Isolated from Peperomia tetraphylla

A recently identified phenylpropanoid isolated from Peperomia tetraphylla was synthesized in enantiopure forms using an aldol condensation of enantiopure （R）-N-acetyl 4-phenyl-oxazolidin-2-one as the key step. With the aid of the single crystal X-ray crystallographic analysis of the synthetic sample, the configuration for the natural product was unambiguously established. Corrected/updated ^13C NMR and optical rotation are also presented.     

Stereoselective Synthesis of Pillar[4]arene[1]cis‐diepoxy‐p‐dione and X‐Ray Crystal Structure of Host–Guest System

Herein, we successfully develop a novel route to give rise to polarity for the pillararenes by the introduction of oxygenated functionalities into pillar[5]arene to stereoselectively synthesize the pillar[4]arene[1]cis ‐diepoxy‐p ‐dione. Its host–guest properties with different dinitrile molecules were also investigated and characterized by NMR and X‐ray crystallography.     

Total Synthesis of Ileabethoxazole,Pseudopteroxazole, and seco‐Pseudopteroxazole

The total syntheses of ileabethoxazole, pseudopteroxazole, and seco‐pseudopteroxazole, three antituberculosis diterpenoids that had been isolated from Pseudopterogorgia elisabethae, were accomplished in a collective fashion. A cascade alkyne carbopalladation/Stille reaction was exploited to construct a triene precursor with suitable geometry. A fully substituted arene was then assembled through a key 6π electrocyclization/aromatization sequence, and served as an advanced common intermediate. Two radical cyclizations led to the formation of the five‐ and six‐membered rings of ileabethoxazole and pseudopteroxazole, respectively, with the desired stereochemistry, and a straightforward side‐chain elongation delivered seco‐pseudopteroxazole.     

Total Synthesis of Ileabethoxazole,Pseudopteroxazole, and seco‐Pseudopteroxazole

The total syntheses of ileabethoxazole, pseudopteroxazole, and seco‐pseudopteroxazole, three antituberculosis diterpenoids that had been isolated from Pseudopterogorgia elisabethae, were accomplished in a collective fashion. A cascade alkyne carbopalladation/Stille reaction was exploited to construct a triene precursor with suitable geometry. A fully substituted arene was then assembled through a key 6π electrocyclization/aromatization sequence, and served as an advanced common intermediate. Two radical cyclizations led to the formation of the five‐ and six‐membered rings of ileabethoxazole and pseudopteroxazole, respectively, with the desired stereochemistry, and a straightforward side‐chain elongation delivered seco‐pseudopteroxazole.     

A High‐Barrier Molecular Balance for Studying Face‐to‐Face Arene–Arene Interactions in the Solid State and in Solution

An atropisomeric molecular balance was developed to study face‐to‐face arene–arene interactions. The balance has a large central 1,4,5,8‐naphthalene diimide surface that forms intramolecular arene–arene interactions with two pendent arms. The balance adopts distinct syn and anti isomers with varying numbers of intramolecular interactions. Thus, the strength of the arene–arene interaction could be quantitatively measured by NMR spectroscopy from the anti/syn ratios. The size of the arene arms was easily varied, which allowed examination of the relationship between arene size and strength of the interaction. A nonlinear size dependence was observed in solution with larger arene arms having a disproportionately stronger arene–arene interaction. The intramolecular arene–arene interactions were also characterized in the solid state by X‐ray crystallography. These studies were facilitated by the kinetic stability of the syn and anti isomers at room temperature due to the high isomerization barrier (ΔG=27.0 kcal mol^?1). Thus, the anti isomer could be selectively isolated and crystallized in its folded conformation. The X‐ray structures confirmed that the anti isomers formed two strong intramolecular arene–arene interactions with face‐to‐face geometries. The solid‐state structure analysis also reveals that the rigid framework may contribute to the observed nonlinear size trend. The acetate linker is slightly too long, which selectively destabilizes the balances with smaller arene arms. The larger arene arms are able to compensate for the longer linker and form effective intramolecular arene–arene interactions.     

ortho‐Directing Chromium Arene Complexes as Efficient Mediators for Enantiospecific C(sp2)–C(sp3) Cross‐Coupling Reactions

A new strategy for the coupling of a broad scope of electronically diverse aromatics to boronic esters is reported. The coupling sequence, which relies on the directed ortho‐lithiation of chromium arene complexes followed by boronate formation and oxidation, occurs with complete ortho‐selectivity and enantiospecificity to give the coupling products in excellent yields and with high functional group tolerance. An intermediate chromium arene boronate complex was characterized by X‐ray, NMR, and IR experiments to elucidate the reaction mechanism.     

Diterpenoid Alkaloids from Aconitum tanguticum

A new 19,21‐secohetisan diterpenoid alkaloid, tangutisine B ( 1 ), was isolated from the aerial parts of Aconitum tanguticum (Maxim. ) Stapf. , together with pacidine, 14‐deacetylajadine. The structure of 1 was determined by an interpretation of 1D‐ and 2D‐NMR together with X‐ray crystallographic data. Bioactivities of the isolates were tested in the P‐388, Bel‐7402, Cox‐2, and caspase‐3 assays.     

Two New Daphniphyllum Alkaloids from Daphniphyllum calycinum

Two new daphniphyllum alkaloids named 2‐hydroxyyunnandaphnine D ( 1 ) and methyl 7‐hydroxyhomodaphniphyllate ( 2 ), together with eight known alkaloids, daphnioldhanin D, calyciphylline F, calyciphylline B, deoxycalyciphylline B, daphnicyclidin H, macropodumine C, 9,10‐epoxycalycine A, and yunnandaphnine A, were isolated from the stems and leaves of Daphniphyllum calycinum. Their structures and relative configurations were established on the basis of spectral evidence (including 2D‐NMR) and subsequently confirmed by a single‐crystal X‐ray crystallographic diffraction analysis.     

A simple and efficient preparation of pyrazolo[3,4‐b]‐pyridine derivatives through an unexpected reaction of cyanothioacetamide under microwave irradiation

An unexpected multicomponent reaction of cyanothioacetamide with aromatic aldehydes and aminopyrazole under MWI was found and reported. It turned out to be an efficient and simple procedure for the preparation of pyrazolo[3,4‐b]pyridine derivatives. The structure of the product was characterized by IR, MS, ¹H and ¹³C NMR, COSY and NOESY spectroscopy, X‐ray crystallographic analysis, and by comparison with the authentic sample prepared with the known procedure. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:694–699, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20497     

A Rare and Exclusive Endoperoxide Photoproduct Derived from a Thiacalix[4]arene Crown‐Shaped Derivative Bearing a 9,10‐Substituted Anthracene Moiety

A rare and exclusive endoperoxide photoproduct was quantitatively obtained from a thiacalix[4]arene crown‐shaped derivative upon irradiation at λ=365 nm; the structure was unambiguously confirmed by ¹H/¹³C NMR spectroscopy and X‐ray crystallography. The prerequisites for the formation of the endoperoxide photoproduct have also been discussed. Furthermore, the photochemical reaction rate could be greatly enhanced in the presence of the thiacalix[4]arene platform because it served as a host to capture oxygen.     

Control of reactivity of phosphine imides by intramolecular coordination with an organoboryl group

Phosphine imides with a boryl substituent 3–5 were synthesized. Their structures were revealed to have a tetracoordinated boron and a phosphorus atom, featuring the N–B coordination by X‐ray crystallographic analysis and NMR spectroscopy. The phosphine imide moiety was persistent to hydrolysis, methylation, and the aza‐Wittig reaction. The N–B coordination remained intact upon treating with pyridine or fluoride ion. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:429–434, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21033     

Terpenoids from Loxocalyx urticifolius

Two new diterpenoids, loxocalyxin A ( 1 ) and 13‐epiloxocalyxin A ( 2 ), and two new sesquiterpenoids, loxocalyxins B and C ( 3 and 4 , resp.), together with three known compounds, were isolated from the MeOH extract of the whole plant of Loxocalyx urticifolius Hemsl . The structures of the new compounds were established by means of spectroscopic analysis including one‐ and two‐dimensional NMR spectroscopy. All new structures were confirmed by X‐ray crystallographic analysis. Their absolute configurations were established.     

一对含有苯甲醛基修饰的杯芳烃异构体的晶体结构以及它们与铽离子配位的光物理性质

Two calix[4]arene isomers with benzaldehyde moieties, i.e., 5,11,17,23-tetra-tert-butyl-25,27-bis[2-(o-formyl-phenoxy)ethoxy]-26,28-dihydroxycalix[4]arene (3) and 5,11,17,23-tetra-tert-butyl-25,27-bis[2-(p-formylphenoxy)-ethoxy]-26,28-dihydroxycalix[4]arene (4), were synthesized according to a newly designed route in high yields, and their crystal structures have been determined by X-ray crystallographic study. The photophysical behavior on complexation of calix[4]arene derivatives 3 and 4 with terbium(Ⅲ) nitrate was investigated in anhydrous acetonitrile at 25℃ by UV-Vis and fluorescence spectroscopies. The crystallographic structure of 3 indicated that the eight oxygen atoms formed a preorganized ionophoric cavity due to intramolecular π-π stacking, which could encapsulate lanthanide ions tightly. In sharp contrast, the compound 4 formed a linear array by intermolecular π-π stacking, hence the oxygen atoms of pendant arms could not coordinate with metal ions, giving a poor binding ability to Tb^3 . The absorption spectra of 3 with Tb^3 showed clearly a new broad intense absorption at 385nm. Interestingly, the narrow emission line spectrum has also been observed for compound 3 with Tb^3 , and the results obtained were discussed from the viewpoint of energy transfer mechanism between host structures and the properties of lanthanide ions.     

Unexpected 1,3‐Dipolar Cycloaddition Reaction of Thiazolo[3,2‐a]pyrimidine Derivatives and Nitrilimine

The 1,3‐dipolar cycloaddition reactions of nitrilimine with thiazolo[3,2‐a]pyrimidine derivatives was investigated. Bis‐cycloadducts were obtained through a domino 1,3‐dipolar cycloaddition/ring‐opening/ring‐opening/1,3‐dipolar cycloaddition processes. The structures of the products were characterized thoroughly by NMR, IR, MS, elemental analysis together with X‐ray crystallographic analysis.     

A Simple,Convenient, and Efficient Synthetic Route for The Preparation of (Z)‐3,5‐Dichloro‐N‐(3‐(4‐substitutedphenyl)‐4‐phenylthiazole‐2(3H)‐ylide)benzamide Heterocyclic Compounds from Aroyl Thiourea Derivatives via S‐cyclization Mechanism

A series of variously substituted 1,3‐thiazole heterocyclic compounds ( 3a – 3d ) were prepared by base‐catalyzed S‐cyclization of corresponding 2,4‐dichloro‐N‐{[(4‐substitutedphenyl)amino]carbonothioyl}benzamide ( 2a – 2d ) with acetophenone in the presence of bromine. The structure of all compounds was established by IR, ¹H‐NMR, ¹³C‐NMR, elemental analysis, and X‐ray crystallographic analysis.     

Synthesis of N1-Substituted 1,2,3,6-Tetrahydropyrimidin-2-ones via an Unexpected Reaction of Thiazolo[3,2-a]-pyrimidine Derivatives and Nitrile Oxide

A new class of N1‐substituted 1,2,3,6‐tetrahydropyrimidin‐2‐ones was prepared in moderate yields by the reaction of nitrile oxide with thiazolo[3,2‐a]pyrimidine derivatives via a domino 1,3‐dipolar cycloaddition/ring‐opening/ substitution process. The structures of the products were characterized thoroughly by IR, elemental analysis, MS, NMR together with X‐ray crystallographic analysis.     

Euphorbiane: A Novel Triterpenoid with an Unprecedented Skeleton from Euphorbia tirucalli

Euphorbiane ( 1 ), a novel triterpenoid exhibiting a unique skeleton, together with seven known compounds were isolated from the 95% EtOH extract of the fresh stems of Euphorbia tirucalli. The structure of 1 and relative stereochemistry were elucidated by extensive NMR and a single‐crystal X‐ray crystallographic analysis.     

New Orsellinic Acid Esters from Fungus Chaetomium globosporum

Seven new orsellinic acid esters, 1 – 7 , and four known compounds were isolated from the solid, fermented rice culture of Chaetomium globosporum (cib‐132). Their structures were elucidated by 1D‐ and 2D‐NMR spectra, and the relative configuration of compound 1 was determined by X‐ray crystallographic analysis.     

Structural Fluctuation of Disilanyl Double‐Pillared Bisheteroarenes

Silacyclophanes possessing two disilanyl pillars were synthesized from tricyclic heteroarenes in one‐pot synthetic procedures. The step‐like anti structures of three congeners bearing two heteroarene units were revealed in single crystals by X‐ray crystallographic analysis. Depending on the structures of aromatic units, torsion angles at the disilanyl pillars altered to maintain the overall step‐like molecular structures. The structure, however, fluctuated between anti and syn conformers in a solution phase despite the presence of eight methyl groups on the ring periphery. The analysis of the coalescence temperature with NMR spectroscopy showed the fundamental energetics of the dynamics. The subtle structural differences affected the dynamic behavior of the silacyclophanes.