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Methoxy-(7a), bromo-(7b), CF3-(7c) and hydroxyl-(7d) substituted bridged triarylamine helicenes were synthesized under mild conditions in 6598% yield. Their luminescence redshifted with π-donating substituents and blue-shifted with the electron-withdrawing CF3-substituent. The absorption and emission of the hydroxyl-substituted derivative (7d) was found to be pH-dependent, particularly under alkaline conditions. Moreover, all derivatives of 7 showed additional reversible negative redox potential, and may be useful as charge transfer materials. [ABSTRACT FROM AUTHOR]

Dimerization of [2,5-bis(fluorodimethylsilyl)phenyl]lithium (8) afforded 9,10-dihydro-9,10-disilaanthracene 9 bearing fluorodimethylsilyl groups at the 2- and 6-positions. Tetrahydrotetrasilapentacene compound 11 was also obtained. [ABSTRACT FROM AUTHOR]

With the objective of preparing an isolable triplet carbene, we have carried out the oxidation of an allenic compound bearing two thioxanthene moieties (5). Relatively weak oxidants such as Ph3C+BF4-gave 8, which is the conjugate acid of 5, as a result of a one-electron oxidation followed by hydrogen abstraction, whereas relatively strong oxidants such as SbCl5furnished a dicationic ketal (9) as a consequence of oxidation and demethylation. Computations on the supposed dicationic intermediate suggest that the singlet state is more stable than the triplet state by 6.7kcalmol-1and that the reason for this peculiarity is because the singlet state is essentially a vinyl cation stabilized by a coordinating methoxy group. [ABSTRACT FROM AUTHOR]

A series of anti-apicophilic pentacoordinate phosphoranes (with one chelating substituent in an O-equatorial, C-apical bonding mode at pentacoordinated phosphorus atom) bearing a para-substituted aryl group (–C6H4(p-X); X = H, CF3, F, OMe) or a mesityl (2,4,6-trimethylphenyl) group were isolated using a novel bulky bidentate ligand with two C2F5 groups. These phosphoranes were stable to isomerization at room temperature, and quantitatively converted into the corresponding more stable isomers (O-apical) at elevated temperatures in solution. On the basis of a kinetic study, the free energy of activation (ΔG‡) of the stereomutation of the O-equatorial mesitylphosphorane to its O-apical isomer was higher than that of the CF3 derivative by 2.6 kcal mol−1, giving rise to a further example of the steric effect of the C2F5 group to freeze the isomerization of the pentacoordinate phosphorus compounds. Kinetic measurements of the isomerization of the O-equatorial ortho-unsubstituted derivatives (–C6H4(p-X)) to the corresponding O-apical isomers suggested that the O-equatorial isomers were stabilized by the π → σ*P–O interaction in the ground state. [ABSTRACT FROM AUTHOR]

Tetrakis(2-pyridyl)stannane (o-Py4Sn), which bears only weakly nucleophilic and Lewis basic pyridines, and a weakly acidic tetraaryltin moiety, was found to efficiently catalyze the reaction between acetic anhydride and alcohols. The reaction rate measurements using 1-phenylethanol show the catalytic activity of o-Py4Sn to be up to 20% of that of 4-(dimethylamino) pyridine (DMAP) and more than 100 times that of pyridine alone. Furthermore, the reaction using (t-BOC)2O was found to be comparable to that with DMAP, with o-Py4Sn being more selective. Thus, a highly efficient cooperative effect is operative with o-Py4Sn. [ABSTRACT FROM AUTHOR]

The reaction of cis-4-oxo-2-pentenal and 8-phenylmenthyl 2-oxocyclopentane-1-carboxylate in the presence of a fluorinated cosolvent afforded the corresponding furan product with a high diastereoselectivity of up to 96% de. Other cyclic β-ketoesters reacted in a likewise diastereoselective manner. [ABSTRACT FROM AUTHOR]

A new dipyrido-annulated N-heterocyclic carbene with phosphorus substituents at the 4 and 8 positions and the corresponding Rh(I) and Rh(III) complexes prepared from the carbene are reported. The X-ray structure of the Rh(I) complex 11 suggested the presence of strong interactions between the phosphorus atoms and Rh(I), in contrast to the previously reported sulfur-substituted system. The new carbene ligand shows promise as a useful carbene-centered pincer ligand with a fixed scaffold for other metal complexes. [ABSTRACT FROM AUTHOR]

Dithienostiboles having a stibole ring fused with a bithiophene system were prepared by the reactions of β,β'-dilithiobithiophene derivatives with aryldichlorostibines. Their optical properties were examined with respect to the UV absorption and emission spectra. DFT calculations on a model were also carried out to understand the electronic states. [ABSTRACT FROM AUTHOR]