Ring Contraction of Tropylium Ions into Benzenoid Derivatives.

We report a method to convert substituted tropylium ions into benzenoid derivatives.

Unusual Alternating Crystallization-Induced Emission Enhancement Behavior in Nonconjugated ω-Phenylalkyl Tropylium Salts.

The alternating physical properties, especially melting points, of α,ω-disubstituted -alkanes and their parent -alkanes had been known since Baeyer's report in 1877. There is, however, no general and comprehensive explanation for such a phenomenon. Herein, we report the synthesis and examination of a series of novel ω-phenyl -alkyl tropylium tetrafluoroborates, which also display alternation in their physicochemical characters.

Tetrabenzo[5.7]fulvalene: a forgotten aggregation induced-emission luminogen.

Tetrabenzo[5.7]fulvalene, one of the first recognized stable members of mixed fulvalenes, has attracted widespread interest for its remarkable structure. However, little has been known about its photoactivity, most likely owing to its very weak luminescence in the solution state.

Stimuli-Responsive Organic Dyes with Tropylium Chromophore.

Tropylium ions possess an interesting combination of structural stability and chemical reactivity due to its Hückel aromaticity and its positively charged polyene nature, respectively. Herein we exploit the chemical versatility and unique structural properties of the tropylium ion to derive a family of novel push-pull organic dyes with strong absorption in the visible range via simple and practical synthetic protocols. These stable organic dyes are highly stimuli-responsive, as demonstrated by their sensitivity towards solvent, pH change, redox reaction, Lewis base and counterion, which marks them as potentially useful compounds for opto-electronic applications.

NHC-Catalyzed Metathesis and Phosphorylation Reactions of Disulfides: Development and Mechanistic Insights.

The development of efficient methods for the metathesis and phosphorylation reactions of disulfide compounds is of widespread interest due to their important synthetic utility in polymer, biological, medicinal and agricultural chemistry. Herein, we demonstrate the use of N-heterocyclic carbenes (NHCs) as versatile organocatalysts to promote these challenging reactions under mild conditions. This metal- and oxidant-free protocol is operationally simple with very short reaction times.

Promotion of Organic Reactions by Non-Benzenoid Carbocyclic Aromatic Ions.

The first three primary members of the non-benzenoid carbocyclic aromatic ion family, namely cyclopropenium, cyclopentadienide, and cycloheptatrienium (tropylium) ions, have planar cyclic structures with (4n+2)π electrons in fully conjugated systems. They fulfill Hückel's rule for aromaticity and hence possess extraordinary stability. Since the historic discovery of tropylium bromide in the late 19th Century, these non-benzenoid aromatic ions have attracted a lot of attention because of their unique combination of stability and reactivity.

N-Heterocyclic olefins as efficient phase-transfer catalysts for base-promoted alkylation reactions.

N-Heterocyclic olefins (NHOs) have very recently emerged as efficient promoters for several chemical reactions due to their strong Brønsted/Lewis basicities. Here we report the novel application of NHOs as efficient phase-transfer organocatalysts for synthetically important alkylation reactions on a wide range of substrates, further demonstrating the great potential of NHOs in organic chemistry.

The Resurgence of the Highly Ylidic N-Heterocyclic Olefins as a New Class of Organocatalysts.

In recent decades, N-heterocyclic carbenes have become established as a prevalent family of organocatalysts. N-Heterocyclic olefins, the alkylidene derivatives of N-heterocyclic carbenes, have recently also emerged as efficient promoters for CO2 fixation and polymerization reactions. Their extraordinarily strong Lewis/Brønsted basicity suggests great potential as a new class of organocatalysts for a broad range of reactions in synthetic chemistry.