Conformational effects in acid-mediated ring opening of epoxides: a prominent role of the oxirane Walsh orbital

A kinetic study has been made of the BF(3)-mediated ring opening of two rigid conformers (alpha and beta) of m- and p-dimethyl-substituted homobenzoquinone epoxides spiro-linked with a twist-boat dibenzocycloheptene ring as compared with the conformationally mobile epoxides bearing diphenyl groups. The rates of the regioselective ring opening were dependent on the topological alignment of the dibenzocycloheptene ring as well as the substitution pattern of the quinone dimethyl groups, indicating pi-aryl participated orbital interaction with the vacant Walsh orbital of the oxirane ring.     

Mechanistic evidence for remote pi-aryl participation in acid-catalyzed ring opening of homobenzoquinone epoxides

The acid-induced reaction of bis(p-chlorophenyl)homobenzoquinone epoxide gave the dual ipso/ortho intramolecular S(E)2-Ar products associated with pi-aryl participated oxirane ring opening, whereas bis(p-tolyl)- and diphenyl-substituted homologues provided only the ortho products.     

Cyclization-Carbonylation-Cyclization Coupling Reaction of Propargyl Ureas with Palladium(II)-Bisoxazoline Catalyst

The cyclization-carbonylation-cyclization coupling reaction (CCC-coupling reaction) of propargyl ureas catalyzed by Pd^II(box) complexes afforded symmetrical ketones bearing two 2-amino-2-oxazoline groups in good to moderate yields.     

A practical strategy to create near-infrared luminescent probes: conversion from fluorescein-based sensors

Luminescent lanthanide complexes incorporating Yb(3+) and Nd(3+) are attracting much attention as imaging agents, but there have been few practical methods to make responsive sensors with these complexes. Here, we introduce a general strategy to synthesize near-infrared luminescent probes by conjugating a Yb(3+) chelate to established fluorescein-based probes. As the first demonstration, we present a complex, based on the green-emitting probe DAF-4, that responds to nitric oxide (NO) in aqueous solution with a significant increase in luminescence intensity at 980 nm.     

Breaking of chiral symmetry and spontaneous rotation in a spinor Bose-Einstein condensate

We show that a spin-1 Bose-Einstein condensate with ferromagnetic interactions spontaneously generates a topological spin texture, in which the m = +/- 1 components of the magnetic sublevels form vortices with opposite circulations. This phenomenon originates from an interplay between ferromagnetic interactions and spin conservation.     

Mg-doping experiment and electrical transport measurement of boron nanobelts

We measured electrical conductance of single crystalline boron nanobelts having α-tetragonal crystalline structure. The doping experiment of Mg was carried out by vapor diffusion method. The pure boron nanobelt is a p-type semiconductor and its electrical conductivity was estimated to be on the order of 10^-3 (Ω cm)⁻¹ at room temperature. The carrier mobility of pure boron nanobelt was measured to be on the order of 10⁻³ (cm² Vs⁻¹) at room temperature and has an activation energy of ∼0.19 eV. The Mg-doped boron nanobelts have the same α-tetragonal crystalline structure as the pristine nanobelts. After Mg vapor diffusion, the nanobelts were still semiconductor, while the electrical conductance increased by a factor of 100-500. Transition to metal or superconductor by doping was not observed.     

Alkaline hydrolysis of N-bromoiminothianthrene derivatives

5-(N-Bromo)iminothianthrene (2) and 5-(N-bromo)iminothianthrene 10-oxide (5) and 10,10-dioxide (8) were prepared and their alkaline hydrolyses were studied. The compound 2 and cis-5-(N-bromo)iminothianthrene 10-oxide (cis-5) afforded the corresponding sulfoximine exclusively. While, unexpectedly, both trans-5-(N-bromo)iminothianthrene 10-oxide (trans-5) and 8 afforded mainly de-brominated products, trans-5-iminothianthrene 10-oxide (trans-4) and 5-iminothianthrene 10,10-dioxide (7), respectively. In these cases, 5-iminothianthrene 5,10-dioxide (6) (Z- and E-mixture) and 5-iminothianthrene 5,10,10-trioxide (9) and further de-iminated products were also formed respectively as minor products. The stereochemical considerations on the S_N reactions are described in view of the steric effect and ‘flip-flap’ motion of the thianthrene framework.     

Photochemical behaviors of tetraphenyldiphosphine in the presence of alkynes

Under an atmosphere of nitrogen, the photoinduced reaction of tetraphenyldiphosphine (1) with alkynes (2) generates vicinal bisphosphinated alkenes (3) as air-sensitive compounds, which can be isolated by treatment with elemental sulfur. A novel E to Z isomerization of 3 is revealed to take place upon continuous photoirradiation.     

Arrays of double-decker porphyrins on highly oriented pyrolytic graphite

Three double-decker complexes of cerium(IV) were synthesized, which commonly have a 5,10,15,20-tetrakis(4-docosyloxyphenyl)porphyrin (C22OPP) moiety as one of the two tetrapyrrole rings. The three complexes-Ce(Pc)(C22OPP), Ce(C22OPP)2, and Ce(BPEPP)(C22OPP)-are distinguished by the other rings, which are Pc (=phthalocyanine), C22OPP, and BPEPP (=5,15-bis[4-(phenylethynyl)phenyl]porphyrin), respectively. The rate of inter-ring rotation of Ce(BPEPP)(C22OPP) was estimated to be approximately 3 s(-1) in solution at room temperature. These complexes assemble into ordered arrays at the interface of 1-phenyloctane and the highly oriented pyrolytic graphite surface, owing to the affinity of the long alkyl chains toward the surface, as revealed by means of scanning tunneling microscopy (STM) with molecular resolution. The shape of the upper ring is reflected in the STM image. Thus, Ce(Pc)(C22OPP), Ce(C22OPP)2, and Ce(BPEPP)(C22OPP) were observed as circular, square, and elliptic features, respectively. Possible molecular arrangements in the array of Ce(BPEPP)(C22OPP) are proposed by comparing STM images and molecular models. In the mixed arrays of Ce(BPEPP)(C22OPP) and H2(C22OPP), the double-decker complexes were distinguished by brighter features. Competitive adsorption experiments showed that the adsorption of Ce(BPEPP)(C22OPP) is less favorable than that of H2(C22OPP) by DeltaG(app) = 2.7 kJ mol(-1). Ce(BPEPP)(C22OPP) molecules appeared elliptic when placed within their own row, while they appeared isotropic when flanked by H2(C22OPP) molecules. Implications of the differences in the observed shapes to the inter-ring rotation are discussed.