Gold(I)-Catalyzed Bis-Cyclization of Allenynes for the Synthesis of Strained and Planar Polycyclic Compounds.

A gold-catalyzed cascade cyclization of naphthalene-tethered allenynes gave strained fused phenanthrene derivatives. The reaction proceeds through the nucleophilic reaction of an alkyne with the activated allene to generate a vinyl cation intermediate, followed by arylation with a tethered naphthalene ring to form the 4H-cyclopenta[def]phenanthrene (CPP) scaffold. When using aryl-substituted substrates on the alkyne terminus, the gold-catalyzed reaction produced dibenzofluorene derivatives along with the CPP derivatives. Selective formation of CPP and dibenzofluorene derivatives depending on the reaction conditions is also presented.

Construction of Tricyclic Nitrogen Heterocycles by a Gold(I)-Catalyzed Cascade Cyclization of Allenynes and Application to Polycyclic π-Electron Systems.

A novel approach to the direct construction of tricyclic nitrogen heterocycles based on gold-catalyzed cascade cyclization of aminoallenynes is described. The expected biscyclization reaction of hydroxyisobutyryl-protected aminoallenynes was efficiently promoted by a catalytic amount of BrettPhosAuNTf2 in the presence of iPrOH to produce 1,2-dihydrobenzo[cd]indole derivatives in good yields. When the reaction was combined with Friedel-Crafts acylation or palladium-catalyzed N-arylation, the resulting tricyclic products were efficiently converted into nitrogen-containing polycyclic aromatic compounds (N-PACs) with highly conjugated π-electron systems. A newly obtained hexacyclic indolium salt showed characteristic concentration-dependent absorption and emission properties.

New Size-Expanded Fluorescent Thymine Analogue: Synthesis, Characterization, and Application.

Here, the synthesis, photophysical characterization, and application of a new size-expanded thymine nucleoside, diox T, is described. diox T has desirable qualities as a T surrogate, including excellent quantum yield (0.36) and high environmental sensitivity. When incorporated into single- and double-stranded DNA, diox T showed excellent photophysical characteristics including a high quantum yield (average 0.20), and unlike BgQ, demonstrated dependence on neighboring bases without significant destabilization of the duplex. Interestingly, the matched base pair of adenine (A) and diox T has the unique property that it exhibits higher fluorescence than mismatched base pairs, and diox T has self-quenching effects. As one example of the possible applications of these promising features, single nucleoside polymorphism typing is demonstrated for discrimination of A by using diox T. The results suggest that diox T can be used for a broad range of applications in chemical biology.