Metal‐Catalyzed Cascade Reactions: Useful Synthetic Tools for the Preparation of Polycyclic Arenes

Abstract

This account summarizes our recent efforts to synthesize numerous important and interesting polycyclic arenes under mild conditions using metal-catalyzed protocols. The palladium-catalyzed annulations of 2-iodobiphenyls or 2,2'-diiodobiphenyls with alkynes efficiently generated phenanthrene derivatives. This synthetic method was utilized as the key step when preparing phenanthrene-based alkaloids, tetrabenzopyracylenes and persubstituted [8]circulenes. Depending on whether a palladium or nickel catalytic system was used, 1-ethynyl-8-iodonaphthalenes underwent either a cyclodimerization or a nitrile-incorporated cascade reaction to produce zethrenes or pyrroloarenes, respectively. Methylene-bridged polyarenes are generated easily from 2-halo-2'-methylbiaryls through benzylic C-H bond activation and subsequent carbon-carbon bond formation, and palladium complexes promote the arylation of methylene carbons. The palladium-catalyzed annulations of 1,8-bis(arylethynyl)naphthalene derivatives with o-diiodoarenes yielded benzo[k]fluoranthene-based linear acenes, which can be applied to synthesize highly curved fragments of fullerenes. The self-reactions of diarylethynes formed either dihydrocyclopenta[a]indenes or octaaryl-1,3,5,7-octatetraenes through palladium-catalyzed cycloisomerization or nickel-catalyzed tetramerization, respectively. In the presence of palladium catalysts, the hydroalkynylation of terminal arylalkynes directly generated angular trimerization adduct dienynes.

Electron‐Deficient Bipyrrole Boomerangs: Bright Fluorophores Obtained via Double C−H Bond Activation

“…[3] Conventional oxidative couplings, typicallyi nduced using stoichiometric quantities of strong oxidants, such as FeCl 3 ,a re however known for their unpredictable selectivity, [4] and are often unsuitable for synthesizing strainedo re lectron-poor aromatics. Existing alternatives, such as reductive Ullmann-type chemistry, [5] dehydrohalogenativec ouplings, [6][7][8][9] and nucleophilic oxidative arylations, [10] generally involve selective prefunctionalization of at least one reacting site. The latter requirementi so bviated by transition metal-mediated double CÀHb ond activation, [11] which has been used as ac arbocyclization method for moderately sized ring systems, [12] but proved to be of limited applicability in the synthesiso fp-conjugated materials.…”

Pd-Induced Double C–H Bond Activation in Annulative Syntheses of Bipyrrole Boomerangs: Mechanistic Insights from NMR Spectroscopy and Computation

“…Furthermore, these methods are often unsuitable for synthesizing strained aromatics , and may fail with electron-poor precursors . Some of these limitations can be overcome with the aid of reductive Ullmann-type chemistry, , dehydrohalogenative couplings, ,− and nucleophilic oxidative arylations, , at the added expense of selective prefunctionalization of at least one reactant. The latter requirement is obviated by transition metal-mediated double C–H bond activation, a powerful synthetic strategy with a rapidly growing scope of use. , In particular, palladium-catalyzed oxidative carbocyclizations have been studied as an annulation method, with recent examples of five- − and six-membered ,− ring closures achieved in moderately sized aromatic systems.…”

Rational Functionalization of a C70 Buckybowl To Enable a C70:Buckybowl Cocrystal for Organic Semiconductor Applications

“…To take advantage of the physical and chemical properties offered by buckybowls, new synthetic methods need to be developed to enable the creation of buckybowls with prescribed shape and functionality. Currently, however, there are no general synthetic routes to these buckybowls, and only a few synthetic pathways exist to create them, for example, flash vacuum pyrolysis (FVP) and solution-phase synthesis . Although FVP has been extensively used to prepare highly strained buckybowls, FVP suffers from low yields, leads to undesired rearrangement of the molecular framework at high temperatures, and has limited functional group tolerance .…”