An alternative synthesis of benzobis(imidazolium) salts via a ‘one-pot’ cyclization/oxidation reaction sequence

Cyclization of N-aryl and N-alkyl 2,5-diamino-1,4-benzoquinonediimines using paraformaldehyde under acidic conditions followed by oxidation with catalytic amounts of Pd(OAc)₂ afforded their respective benzobis(imidazolium) salts in yields of 48-98%. A comparative solid-state study between a 2,5-diamino-1,4-benzoquinonediimine and its corresponding benzobis(imidazolium) dichloride was also performed.     

Diatropicity of 3,4,7,8,9,10,13,14-octadehydro[14]annulenes: a combined experimental and theoretical investigation

The synthesis and study of a series of octadehydro[14]annulenes is described. The aromaticity of these annulenes was investigated through examination of experimental data from arene-fused systems as well as calculated nucleus-independent chemical shifts (NICS) and bond lengths. Benzene ring fusion to the parent system results in a stepwise loss in aromaticity as the number of fused rings is increased from one to two to three. This decrease in annulenic ring current is manifested in the alkene proton chemical shifts (0-2 benzenes) as well as the NICS (0-3 benzenes). Comparison of isomeric thiophene-fused annulenes shows further evidence of ring current competition as these allow for observation of intermittent degrees of delocalization throughout the annulenic core. A consistent relationship between the magnitude of the NICS values and the degree of benzannelation is also observed.     

Synthesis and electronic properties of donor-acceptor pi-conjugated siloles

An efficient method is presented for the synthesis of novel donor-acceptor silole chromophores through selective monohalogenation of 2,5-dimetallosiloles followed by Negishi alkyne cross-coupling reactions. The electronic properties and crystal packing of these new siloles can be controlled through judicious combinations of peripheral functional groups.     

One-pot synthesis of polyrotaxanes via acyclic diene metathesis polymerization of supramolecular monomers

A one-pot synthesis of polyrotaxanes has been developed. The method employs a supramolecular monomer comprising a polymerizable ammonium salt and crown ether, in combination with dynamic ADMet polymerization. Ultimately, highly efficient complexation, polymerization, and end-capping were accomplished in a single operation to yield polyrotaxanes with M(w) up to 19.3 kDa and >80% of the repeat units being complexed.     

Highly efficient synthesis and solid-state characterization of 1,2,4,5-tetrakis(alkyl- and arylamino)benzenes and cyclization to their respective benzobis(imidazolium) salts

[reaction: see text] New synthetic methodology to a variety of 1,2,4,5-tetraaminobenzenes and their corresponding benzobis(imidazolium) salts has been accomplished. Palladium-catalyzed coupling of various 1,2,4,5-tetrabromo- or 1,2,4,5-tetrachlorobenzenes with aryl- or tert-alkylamines afforded the respective tetrakis(N-substituted)aminobenzenes in excellent yields. This enabled comparative solid-state structural analyses of this elusive class of electron-rich arenes with their oxidized derivatives. The tetraamines were found to undergo formylative cyclization to the corresponding benzobis(imidazolium) salts in good to excellent yields.