Crystal structures of the “two” 4‐aminofurazan‐3‐carboxylic acids

The crystal structures of the two compounds reported to be 4‐aminofurazan‐3‐carboxylic acid have been determined. The compound reported by Sheremetev et al. (J Heterocycl Chem 2005, 42, 519) is the actual 4‐aminofurazan‐3‐carboxylic acid. The compound reported by Meyer (Org Prep Proced Int 2004, 36, 361) is the interesting complex formed from a molecule of the acid and a molecule of the potassium salt of the acid. J. Heterocyclic Chem., (2012).     

“Dumbbell”‐ and “Clackers”‐Shaped Dimeric Derivatives of Monocarba‐closo‐dodecaborate

We designed, synthesized, and characterized two types of dimeric forms of monocarba‐closo‐dodecaborate, namely, a “dumbbell”‐shaped dianion having a C?C bond and a “clackers”‐shaped monoanion having an iodonium linker. The unique architectures of these anionic molecules were established by X‐ray analysis. Spectroscopic analysis, DFT calculations, and reactivity experiments revealed high anionic and chemical stability of both anions, which are crucial properties for weakly coordinating anions.     

A highly regioselective synthesis of 1‐n‐methyl‐spiro‐[2,3′“]‐oxindole‐spiro‐[3,2”]indane‐1“, 3”‐dione‐4‐arylpyrrolidines through 1,3‐dipolar cycloaddition protocol

2‐Arylidene‐1,3‐indanediones undergo a regioselective 1,3‐dipolar cycloaddition reaction with the azomethine ylide derived from isatin and sarcosine by decarboxylative route affording a series of 1‐N‐methyl — spiro[2.3′“]oxindole‐spiro[3.2”]indane‐1“,3”‐diones‐4‐aryl pyrrolidines. The structures were established by spectroscopic techniques as well as single crystal X‐ray analysis. Density functional theory at B3L YP/6‐31G^* and the semi empirical AM₁ calculations were employed to rationalize the observed results. The experimental regioselectivity of 1,3‐dipolar cycloadditions could be corroborated nicely with the computed Fukui frontier orbital energies and reaction energies.     

Synthesis of meso‐Pyrrole‐Substituted 22‐Oxacorroles by a “3+2” Approach

Unsymmetrical 22‐oxacorrole containing two aryl groups and one pyrrole group at the meso position was synthesized by condensing one equivalent of 16‐oxatripyrrane with one equivalent of meso aryl dipyromethane under mild acid‐catalyzed conditions followed by oxidation with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ). This [3+2] condensation approach was expected to yield meso‐free 25‐oxasmaragdyrin but unexpectedly afforded unsymmetrical meso‐pyrrole‐substituted 22‐oxacorrole. We demonstrated the versatility of the reaction by synthesizing four new meso‐pyrrole‐substituted 22‐oxacorroles. The reactivity of α‐position of meso‐pyrrole was tested by carrying out various functionalization reactions such as bromination, formylation, and nitration and obtained the functionalized meso‐pyrrole‐substituted 22‐oxacorroles in decent yields. The X‐ray structure obtained for one of the functionalized meso‐pyrrole substituted 22‐oxacorrole revealed that the macrocycle was nearly planar and the meso‐pyrrole was in the perpendicular orientation with respect to the macrocyclic plane. The meso‐pyrrole‐substituted 22‐oxacorroles absorb strongly in 400–700 nm region with one strong Soret band and four weak Q bands. The 22‐oxacorroles are strongly fluorescent and showed emission maxima at ≈650 nm with decent quantum yields and singlet‐state lifetimes. The 22‐oxacorroles are redox‐active and exhibited three irreversible oxidations and one or two reversible reduction(s). A preliminary biological study indicated that meso‐pyrrole corroles are biocompatible.     

Heat‐Induced Supramolecular Organogels Composed of α‐Cyclodextrin and “Jellyfish‐Like” β‐Cyclodextrin–Poly(ε‐caprolactone)

In general, the complexation and gelation behavior between biocompatible poly(ε‐caprolactone) (PCL) derivatives and α‐cyclodextrin (α‐CD) is extensively studied in water, but not in organic solvents. In this article, the complexation and gelation behavior between α‐CD and multi‐arm polymer β‐cyclodextrin‐PCL (β‐CD‐PCL) with a unique “jellyfish‐like” structure are thoroughly investigated in organic solvent N,N‐dimethylformamide and a new heat‐induced organogel is obtained. However, PCL linear polymers cannot form organogels under the same condition. The complexation is characterized by rheological measurements, DSC, XRD, and SEM. The SEM images reveal that the complexes between β‐CD‐PCL and α‐CD present a novel topological helix porous structure which is distinctly different from the lamellar structure formed by PCL linear polymers and α‐CD, suggesting the unique “jellyfish‐like” structure of β‐CD‐PCL is crucial for the formation of the organogels. This research may provide insight into constructing new supramolecular organogels and potential for designing new functional biomaterials. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1598–1606     

60Co γ‐Irradiation‐Initiated “Living” Free‐Radical Polymerization in the Presence of Dibenzyl Trithiocarbonate

The free‐radical polymerization of vinyl monomers in the presence of dibenzyl trithiocarbonate (DBTTC) and under ⁶⁰Co γ‐irradiation is of living character. Under ⁶⁰Co irradiation, the bonds between benzyl group and sulfur were cleaved, benzyl radicals initiate the polymerization. The propagating radical together with trithiocarbonate radicals form a dormant polymer chain. The fast equilibrium between propagation radical and dormant polymer chain controls the polymerization.     

π‐Extended “Earring” Porphyrins with Multiple Cavities and Near‐Infrared Absorption

β,β‐tripyrrin‐bridged earring porphyrins were synthesized through Suzuki–Miyaura cross coupling reactions. These porphyrinoids have multiple cavities and can accommodate two or three metal ions per molecule. The structures of the porphyrins have been elucidated by x‐ray diffraction analysis, and feature curved π planes. The electronic spectra of the porphyrins exhibit near‐infrared (NIR) absorptions and metal insertion leads to red‐shifted and intensified absorption features. Electrochemical analysis and transient absorption measurements indicated that the porphyrins exhibit effective electronic communication between their central and peripheral moieties.     

Reply to “Comment on Aromatic‐Backbone Interactions in Model α‐Helical Peptides”

In response to Van Mourik's comments on our paper (J Comput Chem 2007, 28, 1208.) we present an extended version of our rotation method. We also prove that intramolecular interaction energies as well the basis set superposition errors calculated with our rotation method are comparable with those obtained by the counterpoise method of Boys and Bernardi (Mol Phys 1970, 19, 533). In intramolecular interaction energy calculations, if the interacting groups are in proximity, our rotation method is recommended to avoid artificial interactions, which can be induced by fragmentation. © 2007 Wiley Periodicals, Inc.J Comput Chem, 2008     

Preparation of “Si‐Centered” Chiral Silanes by Direct α‐Lithiation of Methylsilanes

The direct α‐lithiation of methyl‐substituted silanes as an efficient method for the preparation and elaboration of Si‐chiral compounds is reported. Deprotonation of chiral oligosilanes occurs selectively and with high yields at the methyl group of the stereogenic silicon center, even in the presence of multiple methylsilyl or methylgermyl substituents. Computational studies have confirmed this preference as a consequence of pre‐coordination of the lithiating agent by the amino side‐arm and repulsion effects in the corresponding transition state. This complexation is also obvious from X‐ray structure analyses of the α‐lithiated silanes, which exhibit intriguing structure formation patterns differing in the type of aggregation and the amount of alkyllithium used. An alternative route to Si‐chiral compounds is also presented, which involves desymmetrization of dimethylsilanes mediated by a chiral side‐arm. Structure analyses and computational studies have shown that the diastereoselectivity of this α‐lithiation is influenced by the selectivity of the formation of the stereogenic nitrogen upon complexation of the alkyllithium.