Synthesis and Characterization of 1-Hydroxy-4,5-arene-Fused Tropylium Derivatives

A solid noncovalent organic double-helix framework catalyzes asymmetric [6 + 4] cycloaddition

Whereas [4 + 2] cycloadditions are among the most powerful tools in the chemist's synthetic arsenal, controlling reactivity and selectivity of [6 + 4] cycloadditions has proven to be extremely challenging. Such transformations, especially if compatible with simple hydrocarbon-based substrates, could ultimately provide a general approach to highly valuable and otherwise difficult to access 10-membered rings. We report here that highly acidic and confined imidodiphosphorimidate catalysts do not catalyze this reaction under homogeneous conditions. Notably, however, they can spontaneously precipitate an insoluble and double helix-shaped noncovalent organic framework, which acts as a distinctively reactive and stereoselective catalyst of [6 + 4] cycloadditions of simple dienes with tropone.

Syntheses, characterizations and reactions of acene-2,3-dicarbaldehydes

Here, we report improved syntheses, detailed characterizations and reactions of a series of acene-2,3-dicarbaldehydes including tetracene-2,3-dicarbaldehyde. DFT calculations corroborate and complement the experimental results. Tetracene-2,3-dicarbaldehyde and the benchmark organic semiconductor pentacene have isoelectronic π-systems and similar HOMO-LUMO gaps. Tetracene-2,3-dicarbaldehyde is soluble in a host of organic solvents (e.g., DMF, toluene, THF, chloroform, dichloromethane) and shows excellent photooxidative resistance in solution phases exposed to light and air. Further, it is readily sublimed from the solid-state without decomposition, and can be functionalized using different chemistries. We have demonstrated the utility of acene-2,3-dicarbaldehydes as reactants in the syntheses of novel α,α'-diaryl-2,3-acenedimethanols and acenotropones via Grignard reactions and double-aldol condensation reactions, respectively. The acenotropones were further reacted with concentrated H2SO4 to generate hydroxyacenotropylium ions that exhibit long wavelength absorption in the visible and near-IR regions. The optical gap measured for hydroxyanthracenotropylium ion is 1.3 eV. The results gained here implicate acene-2,3-dicarbaldehydes as potential high-value organic semiconductors and as precursors to a host of interesting molecules and materials.

Nickel-catalyzed skeletal transformation of tropone derivatives via C-C bond activation: catalyst-controlled access to diverse ring systems

We report herein on nickel-catalyzed carbon-carbon bond cleavage reactions of 2,4,6-cycloheptatrien-1-one (tropone) derivatives. When a Ni/N-heterocyclic carbene catalyst is used, decarbonylation proceeds with the formation of a benzene ring, while the use of bidentate ligands in conjunction with an alcohol additive results in a two-carbon ring contraction with the generation of cyclopentadiene derivatives. The latter reaction involves a nickel-ketene complex as an intermediate, which was characterized by X-ray crystallography. The choice of an appropriate ligand allows for selective synthesis of four different products via the cleavage of a seven-membered carbocyclic skeleton. Reaction mechanisms and ligand-controlled selectivity for both types of ring contraction reactions were also investigated computationally.

Synthesis of a Series of Tropone-Fused Porphyrinoids

A series of tropone-fused porphyrinoids with unique spectroscopic features has been prepared. A dimethyl tropone-fused pyrrole was reacted with lead tetraacetate to give a bis(acetoxymethyl) derivative that condensed with an α-unsubstituted pyrrole tert-butyl ester to form a tripyrrane intermediate. Cleavage of the tert-butyl ester protective groups, followed by condensation with a series of aromatic dialdehydes and oxidation with DDQ, afforded the tropone-fused porphyrinoid systems. Reactions with pyrrole, furan, thiophene, and selenophene dialdehydes gave tropone-fused porphyrins and related heteroporphyrins. In addition, indene, 4-hydroxybenzene, and 3-hydroxypyridine dicarbaldehydes generated examples of carba-, oxybenzi-, and oxypyriporphyrins. The electronic absorption spectra of the tropone-fused porphyrinoids were greatly altered, showing shifts to longer wavelengths and the appearance of strong Q bands between 600 and 800 nm. The proton nuclear magnetic resonance spectra were also very unusual, as the internal protons were strongly shifted upfield, in some cases giving rise to resonances that approached -10 ppm. However, the external protons showed reduced downfield shifts compared to porphyrinoids that do not have tropone ring fusion. The profound changes observed for these macrocycles demonstrate that the introduction of fused tropone units, together with other structural changes such as core modification, can provide the means by which porphyrinoids with unique spectroscopic properties can be accessed.