Ryuta Miyatake

Synthesis, Stability, and X-Ray Crystallographic Structure Analysis of Spiro[1H-azulenium-1,1′-cycloalkane] Ions

Abstract Direct cycloalkylation of 1,6-dihydroazulene and subsequent hydride abstraction with a trityl salt gave spiro[1H-azulenium-1,1′-cyclopentane and -1,1′-cyclohexane] ions (3 and 4). On the other hand, spiro[1H-azulenium-1,1′-cycloheptane] ion (5) was synthesized from 1-acetylcyclohepta-1,3,5-triene by a sequence involving the Mukaiyama aldol reaction, the Nazarov cyclization, the Shapiro reaction, and hydride abstraction. These cations showed greater kinetic stability than the three- and four-membered ring homologues. Their pKR+ values are far greater compared with those of the known disubstituted tropylium cations and are in the order of the number of carbon atoms at the 1 position, indicating that an inductive effect of the spiroalkyl groups, besides the π-conjugative and σ-conjugative effects, governs the thermodynamic stability. X-Ray crystallographic structure analysis of these cations was also described.

Generation and [4+2] cycloaddition of 1,6-methano[10]annulene-3,4-quinodimethane: a novel synthesis of dimethyl 1,6-methanobenzo[3,4-a][10]annulene-13,14-dicarboxylate ☆

Abstract A new quinodimethane, 1,6-methano[10]annulene-3,4-quinodimethane ( 1 ), was generated and trapped by the Diels–Alder reactions with various dienophiles to provide 1,6-methano[10]annelenes 3 fused with a six-membered ring at the 3,4-positions, one of which was derived to a benzene ring analogue 4 .

A Synthetic Method for Preparing 3,3-Dialkyl-1,2,3,8-tetrahydroazulen-1-one

Abstract The trimethylsilyl enol ether of l-acetylcyclohepta-1,3,5-triene was transformed to 3,3-dialkyl-1,2,3,8-tetrahydroazulen-1-one by a two-step sequence involving the Mukaiyama aldol reaction with ketones and the subsequent Nazarov cyclization.

Synthesis, stability and molecular structure of novel hydrocarbon cations consisting of a tropylium cation and two spiro[4.5]deca-2,4-dienes

Abstract Two novel hydrocarbon cations with a tropylium ion ring fused by two spiro[4,5]deca-2,4-dienes, 9 and 10 , were synthesized by a six-step sequence starting from 1,6- and 1,5-diacetyl-1,3,5-cycloheptatrienes, respectively. The pKR+ values of 9 and 10 were found to be the same at 13.2, providing a new access to highly stable cations. The density functional calculations predict that both 9 and 10 have cyclohexane rings with the chair conformation spread toward molecular edges as the most stable structure. The crystal packing and structure of 9 including dichloromethane were also elucidated by X-ray crystallographic analysis.

Synthesis and stability of 1,1-tetramethylene- and 1,1-pentamethylene-1H-azulenium ions

Abstract Direct cycloalkylation of 1,6-dihydroazulene and subsequent hydride abstraction with trityl salt gave the title cations 3 and 4 . These cations showed greater kinetic stability than the three- and four-membered ring homologs, and their p K R + values indicated greater thermodynamic stability compared with the known disubstituted tropylium cations.

Dispiro[cyclohexane-1,1'-(1', 7'-dihydrocyclopenta[f]azulenium)-7', 1 -cyclohexane] perchlorate, a new highly stable hydrocarbon cation

Abstract The title cation was synthesized from 1,6-diacetylcyclohepta-1,3,5-triene by a six-step sequence involving an aldol reaction, the Nazarov cyclization, the Shapiro reaction and hydride abstraction, and its p K R+ value was found to be 13.2, providing a new access to highly stable hydrocarbon cations.

Crystal structure ofS-hexyl (E)-3-(4-methylbenzylidene)dithiocarbazate

In the title compound, C15H22N2S2, the dithiocarbazate group adopts an E conformation with respect to the C=N bond of the benzylidene moiety. In the crystal, molecules are linked by pairs of N—H⋯S hydrogen bonds, forming inversion dimers with an R 2 2(8) ring motif. The dimers are linked via C—H⋯π interactions, forming chains propagating along [100].

Dicyclopenta[a,d]cyclooctene: A [14]Annulene Containing Two Zero-Atom Cross-Links

14π-Electrocyclization across the two pentafulvenoid moieties of pentafulvene 1 occurs upon heating to provide dicyclopenta[a,d]cyclooctene 2 [Eq. (1)]. The nonalternant hydrocarbon 2 shows diatropic character and a distinctive absorption spectrum with the longest wavelength maximum at 767 nm.

1,1-ETHYLENE-1H-AZULENIUM ION AND ITS ALKYL SUBSTITUTED DERIVATIVES : SYNTHESIS, CHARACTERIZATION, AND SOME REACTIONS THEREOF

Abstract 1,1-Ethylene-1H-azulenium tetrafluoroborate (1b) and its alkyl substituted derivatives, 6-t-butyl (1c) and 4-isopropyl-3,8-dimethyl ones (1d), were synthesized starting from their corresponding azulenes by a three-step sequence which includes reduction, cyclopropanation and hydride abstraction reactions. The cation 1 b and its 6-t-butyl derivative 1c, generated in deuterated acetonitrile at −20 °C, were characterized by low-temperature NMR spectroscopy. On the other hand, the cation 1d was isolated as slightly unstable, greenish-yellow crystals. While the cation 1 b in solution underwent expansion of the cyclopropane ring at elevated temperatures, 1 c and 1 d just decomposed. All the cations were found to react easily with nucleophiles to give thermodynamically controlled, stable addition products at their cyclopropane methylene carbons.

SYNTHESIS AND REACTIONS OF 1,1-TRIMETHYLENE-1H-AZULENIUM ION

Abstract Direct cyclobutylation of 1,6-dihydroazulene gave the spiro hydrocarbon 6 , which was subjected to hydride abstraction to lead to the title cation 4 . Its hexafluorophosphate salt was isolated as crystals. The cation 4 showed distinctive chemical behavior compared with its three-membered ring homolog.