Palladium-Catalyzed Double Annulations To Construct Multisubstituted Benzodifurans

Transition metal catalysed cascade C-C and C-O bond forming events of alkynes

The past few decades have witnessed the emergence of domino reactions as a powerful tool for the multi-functionalization of alkynes for the rapid and smooth construction of complex molecular architectures. In this context, employing transition metal catalysis, vicinal/geminal cascade functionalization of alkynes involving C-C and C-O bond-formation reactions, has become a preferred strategy for the synthesis of oxygenated motifs. Despite this significant progress, reviews documenting such strategies are either metal/functional group-centric or target-oriented, thus hampering further developments. Therefore, in this review, different conceptual approaches based on C-C and C-O bond-forming events of alkynes such as carboxygenation (C-C and CO bond formation), carboalkoxylation (C-C and C-OR bond formation), and carboacetoxylation (C-C and C-OAc bond formations) are discussed, and examples from the literature from the last two decades are presented. Further, we have presented detailed insights into the mechanism of different transformations.

Hydrazone–Pd-catalyzed direct intermolecular reaction of o-alkynylphenols with allylic acetates

The hydrazone–palladium catalyzed direct intermolecular reaction of o-alkynylphenols with allylic acetates gave the corresponding 2-substituted-3-allylbenzofuran derivatives at room temperature.

Hydrazone–palladium catalyzed annulation of 1-cinnamyloxy-2-ethynylbenzene derivatives

The annulation of 1-cinnamyloxy-2-ethynylbenzene derivatives using a hydrazone–palladium catalyst system proceeded smoothly and gave the corresponding 2-substituted-3-cinnamylbenzofurans in good-to-excellent yields.

Highly selective intramolecular addition of C–N and S–N bonds to alkynes catalyzed by palladium: a practical access to two distinct functional indoles

Palladium-catalyzed highly selective intramolecular addition of C–N and S–N bonds to alkynes has been achieved, and two distinct kinds of functional indoles were synthesized rapidly from the same set of substrates in a catalyst-controlled manner.

Palladium-catalyzed intramolecular addition of C–N bond to alkynes: a novel approach to 3-diketoindoles

Palladium-catalyzed intramolecular addition of C–N bond to alkynes to synthesize highly functional 3-diketoindoles has been achieved.

Ring-closing metathesis reactions of bis(enynes): selectivity and surprises

A study of the ring-closing metathesis reactions of two bis(enynes) is presented. These substrates, which contain two alkenes and two alkynes, as well as a resident stereocenter, can potentially generate metathesis products resulting from many reaction pathways. In this contribution we present our results on these reactions, show how small changes in reaction conditions can lead to different product ratios, and attempt to provide a rationale for the outcomes.

Direct assembly of 3,4-difunctionalized benzofurans and polycyclic benzofurans by phenol dearomatization and palladium-catalyzed domino reaction

A method to directly convert 2-alkynylphenols to 3,4-difunctionalized benzofurans and polycyclic benzofurans was developed. This protocol involves a hypervalent-iodine-mediated oxidative dearomatization to break the aromaticity of 2-alkynylphenols, and a palladium-catalyzed domino reaction to install two functional groups at the C3 and the C4 positions and restore the aromaticity of benzofurans.

Rhodium-catalyzed intramolecular hydroarylation of 1-halo-1-alkynes: regioselective synthesis of semihydrogenated aromatic heterocycles

The regioselective intramolecular hydroarylation of (3-halo-2-propynyl)anilines, (3-halo-2-propynyl) aryl ethers, or (4-halo-3-butynyl) aryl ethers was efficiently catalyzed by Rh2(OCOCF3)4 to give semihydrogenated aromatic heterocycles, such as 4-halo-1,2-dihydroquinolines, 4-halo-3-chromenes, or 4-(halomethylene)chromans, in good to excellent yields. Some synthetic applications taking advantage of the halo-substituents of the products are also illustrated.

Carbazolyl benzo[1,2-b:4,5-b']difuran: an ambipolar host material for full-color organic light-emitting diodes

We have designed an ambipolar material, 3,7-bis[4-(N-carbazolyl)-phenyl]-2,6-diphenylbenzo[1,2-b:4,5-b']difuran (CZBDF), and synthesized it by zinc-mediated double cyclization. Its physical properties clarified that CZBDF possesses a wide-gap character, well-balanced and high hole and electron mobilities of larger than 10(-3) cm(2) V(-1) s(-1), and a high thermal stability. Using CZBDF as a host material for heterojunction OLED devices, a full range of visible emission was obtained. Notably, CZBDF also enabled us to fabricate RGB-emitting homojunction OLEDs, with performances comparable or superior to the heterojunction devices composed of several materials.

Versatile strategy to access fully functionalized benzodifurans: redox-active chromophores for the construction of extended pi-conjugated materials

An efficient synthetic approach to construct a fully substituted benzo[1,2-b:4,5-b']difuran (BDF) 2a via base-catalyzed double annulations is presented. Compound 2a can readily undergo Suzuki, Heck, and Sonogashira coupling reactions to afford in good yields a manifold of extended pi-conjugated BDF derivatives, e.g., with pyridine termini (4-6) and with different spacers. These are highly luminescent materials that undergo two reversible one-electron oxidations. Remarkably, their photophysical and electrochemical properties can be largely tuned by methylation or protonation. Consequently, they can function as pH-dependent fluorescence switches. Finally, the observed electronic properties are explained on the basis of density functional theory.