Sarah P. Luppino

Naphthazarin-Polycyclic Conjugated Hydrocarbons and Iptycenes

The synthesis of a set of naphthazarin-containing polycyclic conjugated hydrocarbons is described herein. Sequential Diels-Alder reactions on a tautomerized naphthazarin core were employed to access the final conjugated systems. Complete conjugation across the backbone can be achieved through complexation with BF2, as observed by 1H NMR analysis and UV/vis spectroscopy. Precise synthetic control over the degree of oxidation of naphthazarin quinone Diels-Alder adduct 10 is additionally demonstrated and enables us to direct its subsequent reactivity. Finally, this work serves to demonstrate the potential for naphthazarin as a building block in the synthesis of novel organic electronic materials.

Taking the Dimers Out of Diazaheptacenes

Significance: The authors have successfully designed, synthesized, and isolated the first persistent azaheptacene. The diazaheptacene in this work required four Si(s-Bu)3-ethynyl groups to effectively prevent dimerization upon oxidizing to the final product 4. Comment: The key synthetic step was the fast oxidation using manganese oxide to convert 3 into 4, which was carried out for no longer than forty seconds. The product 4 was stable for approximately one hour, after which dimerization products were detected. Alternative trialkylsilyl-ethynyl groups, such as the TIPS-ethynyl group, proved ineffective at impeding dimerization. 18% yield palladium pre-cat. Cs2CO3 dioxane

Aryne’t You Doubly Impressed with this Cyclopropenone Insertion?

Significance: The authors demonstrate a method to formally insert two aryne units into the carbon– oxygen double bond of a ketone, producing spirocyclic xanthene–cyclopropene scaffolds 1. Mechanistically, a direct formal [2+2] cycloaddition of an aryne with cyclopropenone is followed by the subsequent cycloaddition of the ortho-quinone methide intermediate with the second aryne equivalent. Comment: The reaction relies on the strong nucleophilicity of the ketone oxygen: cyclopropenone proved to be one of the best candidates due to its zwitterionic structure, and attempts to generalize the reaction with other ketones failed. Interestingly, the more electron-rich aryne precursor, when exposed to trace acid, ring-opened to produce xanthylium triflate 2. Selected examples: 14 examples up to 80% yield MeCN, 30–60 °C, 24 h OTf