Takanori Kajioka

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.

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 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.

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 conformation of 3,10-di(t-butyl)- and 3,10-dichloro-4,9-methanothia[11]annulenes

First two derivatives of 4,9-methanothia[11]annulene, 3,10-di(t-butyl)- and 3,10-dichloro-4,9-methanothia[11]annulenes (4 and 5), were synthesized from the diketosulfide 6. Spectroscopic properties and X-ray crystallographic analyses revealed that 4 exists as an anti-conformer in respect of stereochemical relationship between the methano bridge and the sulfur atom both in solid state and in solution, while 5 exists as a syn-conformer in similarity to the parent of 4,9-methanothia[11]annulene (3).

REACTION OF 1-(ETHOXYCARBONYLACETYL)- CYCLOHEPTA-1,3,5-TRIENE WITH ACETIC ANHYDRIDE: A FACILE SYNTHESIS OF 1-ACETOXY- 2-ACETYLAZULENES

ABSTRACT Reaction of 1-(ethoxycarbonylacetyl)cyclohepta-1,3,5-triene (1) with acetic anhydride in the presence of sodium acetate gave 1,3-diacetoxy-2-acetylazulene (2) in 26% yield. On the other hand, a similar reaction in the presence of sodium acetate and aluminium chloride provided 1-acetoxy-2-acetyl-3-methylazulene (5) as a major product in 19% yield, accompanied with a 9% yield of 2.