Kunihide Fujimori

Synthesis, stability and bonding situation of tris-, bis- and mono[9-(azuleno[1,2-b]thienyl)]methyl cations

Stable tris-, bis- and mono[9-(azuleno[1,2-b]thienyl)]methyl cations (7a, 8a and 9a) and their derivatives, with a 6-isopropyl substituent on each azuleno[1,2-b]thiophene ring (7b, 8b and 9b) were prepared by the hydride abstraction reaction of the corresponding methane derivatives. The bonding situation of these compounds including the methane derivatives was examined by analysis of the 3J(H,H) values for the seven-membered ring from the 1H NMR spectra. The methane derivatives exhibited a significant alternating pattern in the 3J(H,H) values, which indicated that the pi-system of the azulene core is perturbed by the fused thiophene ring, showing a tendency towards a localized heptafulvene substructure. The 3J(H,H) values of 7b and 8b in the seven-membered ring revealed that the alternating C-C bond lengths in the azulene core still existed. The cations 9a and 9b, which exhibited nearly equal 3J(H,H) values in the seven-membered ring, exhibit the development of a delocalized tropylium substructure in the azulene core. X-ray crystal analysis of 6-isopropylazuleno[1,2-b]thiophene revealed substantial bond-length alternation in the seven-membered ring. Significant bond-length equalization in the seven-membered ring was also confirmed by the X-ray crystal analysis of 9b. The stability of these carbocations was examined by measurement of the pKR+ values and the redox potentials, which revealed that the bond-length alternation in the azulene core does not significantly affect the stability of the carbocations.

Synthesis and properties of novel bis(1,3-benzodithiolium)-type dications containing a biaryl unit: New redox systems undergoing reversible structural changes by electron transfer

In order to develop new redox systems which undergo reversible structural changes by electron transfer, bis(1,3-benzodithiolium)-type dications (5 2+ ) containing a biaryl unit have been synthesized by hydride abstraction of the corresponding bis(1,3-benzodithiol-2-yl)biaryls (8). Reduction of 5 2+ with zinc gave the corresponding intramolecular cyclization products (6), which reverted to 5 2+ by oxidation. Cyclic voltammetry also showed the efficient interconversion between both states. X-Ray analyses revealed that the twist angle of the biaryl unit decreases largely by reductive intramolecular cyclization.

Structure of azuleno[1,2-b]thiophene

C12H8S, m.p. 375-376 K, orthorhombic, Pnma, a = 7.954 (2), b = 19.194 (5), c = 6.021 (2) A, D m = 1.33, D x = 1.332 Mg m -3, Z = 4. Final R = 0.105 for 504 reflexions. The molecules form a sheet parallel to (010). The sheets are stacked along b. The structure is disordered as in azulene. The molecule is planar within 0.06 (2)A. The bond-length alternation in the seven-membered ring is significant, the shortest C-C length being 1.27 (2) A between positions 5 and 6 (C(7)-C(8)), and the longest 1.58 (2)A between 4a and 9a (C( 11)-C(12)). 1.2 + 0.15 tan 0) using Ni-filtered Cu radiation (2 = 1.5418 A) at 40 kV and 200 mA. Background was measured for 5 s on either side of the peak. Three reference reflexions showed no intensity deterioration. The intensities were corrected for Lorentz and polarization factors, but not for absorption (p(Cu Kct) = 2.59 mm-l). In total 587 independent reflexions were collected, of which 504 with IFol > o(F) were used in the refinement. The structure was solved by the Patterson method. At first the space group was assumed to be Pn21a based on the molecular symmetry and Z = 4. A

Synthesis of 1,2-azulenequinone derivatives by bromine-oxidation

Treatment of 2-hydroxyazulene (la) with 3 equiv. of C 5 H 5 N·HBr 3 in aqueous THF-AcOH at 0 °C for 1 h afforded l,l,3-tribromoazulene-2-one (5a). 3-Bromo-l,2-azulenequinone (2a) was obtained by the hydrolysis of 5a in the presence of Ag 2 O. Annulated compound 6 was readily obtained by the reaction of 2a with o-phenylenediamine.

Synthesis and properties of bis(1,3-benzodithiole)-type redox systems containing a xylyl rotator unit: A new type of redox-responsive molecular rotor

A new type of redox-responsive molecular rotors (3 2+ /4) possessing a xylyl rotator unit have been designed and synthesized. Reduction of 3 2+ with zinc gave the corresponding cyclization products (4), from which dications (3 2+ ) were regenerated upon oxidation. Cyclic voltammetry also showed the interconversion between 3 2+ and 4. Variable-temperature 1 H NMR measurements revealed that the rotational barriers of the xylyl units in the neutral states (4) are higher than those in the dication states (3 2+ ).

Synthesis of azulenequinones fused with thiophene and furan

1,5- And 1,7-azulenequinones fused with a thiophene or furan ring have been synthesized by bromine oxidation of azuleno[1,2-b]thiophenes, azuleno[2,1-b]thiophene, and azuleno[1,2-b]furan in aqueous THF.

Annelated dehydroannulenes fused with azulene ring. The synthesis of bisdehydro[14]- and -[16]annuleno[a]azulene

Abstract 10,12-Bisdehydro-3-isopropyl-9,14-dimethyl[14]- and -11,16-dimethyl[16]annuleno[a]azulene in which the conjugated 14- and 16-membered rings are fused to azulene ring, have been synthesized. It was found that the fusion of azulene ring suppresses the diatropicity of [4n+2], 14π-electron system to a smaller extent than benzene ring.

Out-of-plane deformation of the azulene ring along its short molecular axis in crystal and theoretical structures of 1,3-diheterolyl- and 1,3-diphenylazulenes

Crystal structures of four simple azulene derivatives, 1,3-diheterolyl-and 1,3-diphenylazulenes, were determined by X-ray diffraction analysis. Three of them showed clear out-of-plane deformation of the azulene ring along its short molecular axis, and one showed a similar but very small deformation. Structural and conformational analyses on substituted azulenes were also performed by DFT molecular orbital calculations. Based on the results of the calculations it was indicated that azulenes could exhibit such deformation depending on their conformations except one case, supporting the results of X-ray analysis. A similar deformation was also found in the crystal structure of a previously reported 1,3-disubstituted azulene whose data were collected from an X-ray crystal structure database.

One-way cis → trans photoisomerization of azulenylethenes

Abstract 2-Styrylazulene (2) and 1,2-di(azulenyl)ethene (3) undergo one-way cis → trans isomerization on direct irradiation and on triplet sensitization. The quantum yield of cis → trans isomerization (φc → t) on triplet sensitization increases with the initial cis isomer concentration and exceeds unity ( φ c → t = 25 at [cis- 2 ] = 17. × 10 −3 M ). The quantum yield of cis → trans2 and 3 are in the region of 10−3 on direct irradiation at the higher excited singlet state S2, but increase with increasing concentration of the cis isomer. These results strongly indicate that, even on direct irradiation of 2-azulenylethenes, one-way cis → trans isomerization takes place as a quantum chain process in the excited triplet state after intersystem crossing.

Reactions of tosylhydrazones of 2-methoxy-1-azaazulene-3-carboxaldehyde and azulene-1-carboxaldehyde with styrenes and stilbenes

The reactions of sodium salt of 2-methoxy-1-azaazulene-3-carboxyaldehyde tosylhydrazone with styrenes gave 3,8-cyclohexeno-2-methoxy-1-azaazulenes and 3-cyclopropyl-2-methoxy-1-azaazulenes. The formers were afforded through the diazo compound generated from the tosylhydrazone and the latters were yielded via the carbene derived from the diazo compound. The reactions with stilbenes gave the corresponding cyclopropane derivatives. The similar reactions with sodium salt of azulene-1-carboxaldehyde tosylhydrazone gave the analogous result