Kimiaki Yamamura

Hydrogen-bonding-based thermochromic phenol–amine complexes

Variable-temperature UV–vis, 13C NMR and IR studies showed that proton-transferred complexes were formed between phenols and amines in apolar solvents at low temperature. Upon cooling a solution of p-nitrophenol and diisopropylamine in toluene, the colour of the solution changed from colourless to yellow. This thermochromism was ascribed to the proton transfer in the hydrogen-bonding complex. Under UV–vis conditions, butylamine and imidazole also caused similar thermochromism upon complexation with p-nitrophenol, while triethylamine, quinuclidine and pyridine did not. The thermochromic behaviour was particularly dependent on the stoichiometry of the amine and the phenol: a solution of 3,3′-dibromo-5,5′-dinitro-2,2′-biphenyldiol and diisopropylamine with a molar ratio of 1:1 showed no thermochromism, while solutions with 1:2 or higher ratios showed thermochromism, indicating that excess amine is required to obtain the proton-transferred species. These results revealed that the proton-transferred species forms in apolar solvents at low temperature if an appropriate hydrogen-bonding network between the phenol and the amine can stabilize it.

Three dimensional supramolecules of triptycene-quinone and its 6,7-dimethyl derivative formed by weak intermolecular π-π interactions and CH···O hydrogen bonds

Abstract The crystal structures of 9,10-dihydro-9,10-[ o ]benzenoanthracene-1,4-dione (TPQ) and its 6,7-dimethyl derivative (6,7-dimethyl-TPQ) were studied. In the latter crystal ribbon-like supramolecules were found to be formed by weak intermolecular π-π interactions between quinone and benzene moieties of the molecules. Similar π-π interaction seems to be present in TPQ. Moreover, the supramolecules were found to be associated each other by CH···O hydrogen bonds to result in three dimensional supramolecules.

An efficient novel synthesis of β-(azuleno[1,2-b]benzothienyl)- and β-(azuleno[2,1-b]benzothienyl)-α,β-unsaturated ketones by the tropylium ion-mediated intramolecular furan ring-opening reaction and X-ray investigation of methyl ketone derivative

Intramolecular reaction of 2-tropylio-3-(5-substituted 2-furyl)benzothiophenes (3), prepared from the corresponding 2-cycloheptatrienyl-3-(5-substituted 2-furyl)benzothiophenes (2), afforded the β-(azuleno[1,2-b]benzothienyl)-α,β-unsaturated ketones (4), which are otherwise difficult to obtain, in moderate yields. The reaction involves a ring-opening process of the furan ring by intramolecular attack of the tropylium ion onto the 2-position of the furan ring. Similarly, β-(azuleno[2,1-b]benzothienyl)-α,β-unsaturated ketones (8) were obtained from the corresponding 3-tropylio-2-(5-substituted 2-furyl)benzothiophenes (7) albeit in lower yields. The molecular and crystal structures of the methyl ketone derivative, 8a, are discussed on the basis of X-ray structure analysis.

Synthesis of pyrylium salts from trisubstituted 1,4-pentadiyn-3-ols with HClO4

Abstract The synthesis of 2,4,6-trisubstituted pyrylium salts from 1,3,5-trisubstituted 1,4-pentadiyn-3-ols with HClO 4 is reported for the first time.

Novel and facile synthesis of β-(4-azuleno[1,2-b]thienyl)- and β-(4-azuleno[2,1-b]thienyl)-α,β-unsaturated ketones by intramolecular tropylium ion-mediated furan ring-opening reaction

The novel and efficient methods for the synthesis of β-(4-azuleno[1,2-b]thienyl)-α,β-unsaturated ketones (1) and β-(4-azuleno[2,1-b]thienyl)-α,β-unsaturated ketones (2) have been described. Refluxing the dichloromethane solutions of 2-tropylio-3-(2-furyl)thiophene tetrafluoroborates (3) or 3-tropylio-2-(2-furyl)thiophene tetrafluoroborates (4) afforded (1) and (2), respectively, in moderate yields. The reaction involves an intramolecular tropylium ion-mediated furan ring-opening reaction.

A characteristic ribbon-like supramolecular structure and intermolecular D–A interactions in the crystals of triptycenequinones, triptycene-TCNQs and their clathrates as studied by X-ray investigations

Abstract A common ribbon-like structure was found in the crystals of triptycenequinones (TPQs), triptycene-TCNQs (TP-TCNQs) and their clathrates. The characteristic structure can be regarded as a supramolecular unit the formation of which is aided by weak intermolecular D–A interactions. This view is supported by the host–guest D–A interactions appeared in the crystals of the clathrates of 5,8-dimethyl-TPQ and 5,8-dimethoxy-TP-TCNQ. Intermolecular C–H⋯O hydrogen bonds seem to be present in TPQ derivatives.

SYNTHESIS OF 4-(AZULENO[b]INDOLYL)-3-BUTEN-2-ONES BY INTRAMOLECULAR TROPYLIUM ION-MEDIATED FURAN RING-UNRAVELLED REACTION

4-(l-Benzenesulfonyl-6-azuleno[l,2-b]indolyl)-3-buten-2-one (1) and 4-(l-benzenesulfonyl-11-azuleno[2,1-b]indolyl)-3-buten-2-one (2) were synthesized from 1-benzenesulfonyl-3-(5-methylfuryl)-2-tropylioindole (10) and l-benzenesulfonyl-2-(5-methylfuryl)-3-tropylioindole (14), respectively. The synthetic method is based on furan ring-unraveled reaction by the intramolecular electrophilic attack of the tropylium ion. 4-(6-Azuleno[l,2-b]indolyl)-3-buten-2-one (3) and 4-(ll-azuleno[2,1-b]indolyl)-3-buten-2-one (4) could be easily obtained from 1 and 2, respectively. Treatment of 3 and 4 with iodomethane gave N-methyl derivatives, 4-(l-methyl-6-azuleno[1,2-b]indolyl)-3-buten-2-one (5) and 4-(1-methyl-11-azuleno[2,1-b]indolyl)-3-buten-2-one (6), respectively, in moderated yield. The compounds, 1, 2, 3, 4, 5, and 6, which include the novel tetracyclic π conjugated azulene nuclei, are the azuleno[b]indole analogues of benzalacetone.

Lewis acid catalyzed substitution of allylic nitro compounds with cyanotrimethylsilane

Abstract The nitro group in allylic nitro compounds is replaced by cyano group on treatment with cyanotrimethylsilane in the presence of Lewis acid.

Unequivocal existence of a centrosymmetric associated dimer of 4-(4-azuleno[1,2-b]thienyl)but-3-en-2-one formed by CH…OC hydrogen bonds in the crystals

Abstract Unequivocal existence of a centrosymmetric associated dimer of the title compound 1 formed by CH…OC hydrogen bonds was found by X-ray crystallography. The occurrence of this hydrogen bond, as well as the observed reduction of the bond-length alternation in the seven-membered ring of 1 , is understandable by the dipole resonance structures of the compound.

Novel synthesis of β-substituted β-diphenylmethylstyrenes from β-substituted β-methylstyrenes in the presence of palladium(II) acetate

β-Substituted β-methylstyrenes react with benzene in the presence of palladium(II) acetate to produce the corresponding (E)- and/or (Z)-β-substituted β-diphenylmethylstyrenes in good yields. A mechanism involving a 2-substituted 3,3-diphenylpropene intermediate is suggested. The configurations of the products are discussed.