A Direct Approach to 5-Hydroxybenzofurans via a Platinum-Catalyzed Domino Rearrangement/5-endo-dig Cyclization Reaction of Quinols

Synthesis of Benzofuran Derivates via a Gold-Catalyzed Claisen Rearrangement Cascade

A novel method toward a facile synthesis of diverse benzofuran derivates from easily obtained quinols and alkynyl esters has been reported. A gold-catalyzed intermolecular alkoxylation/Claisen rearrangement/condensation cascade was involved. The introduction of difluorodiphenylsilane as a water-trapping reagent in the reaction leads to a higher yield.

Recent advances in the cascade reactions of enynols/diynols for the synthesis of carbo- and heterocycles

This review summaries a view of the advances in the cascade reactions of enynols/diynols for the construction of carbo- and heterocycles.

Gold (I)-Promoted Intermolecular Cascade Annulation to Access 2-Hydroxybenzocarbazoles via a Meyer-Schuster Rearrangement

An efficient cascade annulation protocol was established to access substituted 2-hydroxybenzocarbazoles from alkynylcyclohexadienones and substituted 2-aminophenols under gold catalysis. In this transformation a new C-C, two C-N bonds were formed sequentially and moderate to excellent yields of 2-hydroxybenzocarbazole derivatives were obtained selectively via Meyer-Schuster rearrangement in one-pot.

Gold-Catalyzed Synthesis of 6-Hydroxyindoles from Alkynylcyclohexadienones and Substituted Amines

An efficient gold-catalyzed formation of 6-hydroxyindoles from substituted alkynylcyclohexadienones and amines have been developed. In this reaction two new C-N bonds were formed, and moderate to very good yields of the 6-hydroxyindole derivatives were obtained in one pot. This organic transformation tolerates a range of substituted alkynylcyclohexadienones and amines, which resulted in 6-hydroxyindole derivatives selectively.

Intramolecular Electrophilic Cyclization Approach to 6-Substituted Naphtho[2,1- b]benzofurans: Novel Dual-State Emissive Fluorophores with Blue Emission

A regiospecific synthesis of naphtho[2,1- b]benzofurans with a substituent at the C6 position was achieved via intramolecular 6-endo-dig electrophilic cyclization under acidic conditions to construct the central aromatic C ring. Screening of the synthesized compounds using a high-content imaging system enabled us to discover novel dual state emissive compounds 2{ 1,6}, 2{ 1,8}, and 2{ 4,3}, which are highly emissive with blue emission in their solid states as well as in solution states in most solvents. In addition, the compounds 2{ 4,3}, 2{ 4,12}, and 2{ 5,13} were found to be the most cell permeable in HeLa cells for live cell imaging with negligible phototoxicity.

5-Endo-dig cyclizations in organic syntheses

The favorability of ring closure reactions as per Baldwin rules has gained immense importance recently. This is evident from the current literature such as research articles, reviews, and books that have been published in this area. This review covers the recent applications of 5-endo-dig cyclization in organic synthesis focusing in the last two decades. A variety of 5-membered heterocycles as well as carbocycles could be synthesized via 5-endo-dig cyclization reactions. The important applications of 5-endo-dig cyclization in organic synthesis covering different aspects have been summarized in this review.

Symmetry-based approach to oligostilbenoids: Rapid entry to viniferifuran, shoreaphenol, malibatol A, and diptoindonesin G

The recognition of the local symmetric image within benzofuran-based natural oligostilbenoids guided us to design a modular synthetic approach to these molecules by utilizing a three-step sequence consisting of Sonogashira coupling, iodocyclization, and Suzuki coupling. During our synthesis, the relative reactivities of ester, aldehyde, and alkoxy groups on the same aryl ring toward the neighboring alkyne in the iodine-mediated cyclization reactions were explored. Starting from the symmetrical 3,5-dimethoxybenzyl alcohol, this route allowed rapid access to 2,3-diarylbenzofuran, a key intermediate to several oligostilbenoid natural products, in good overall yields.

Syntheses of pterocarpenes and coumestans via regioselective cyclodehydration

A highly efficient synthetic route to pterocarpenes and coumestans is described. BCl3-mediated dehydrative cyclization of 1,3-diaryloxyacetones under mild conditions permitted regioselective ring closure to afford 3-((2-iodoaryloxy)methyl)benzofurans which were converted to the corresponding pterocarpenes by Pd-catalyzed intramolecular direct arylation. The subsequent benzylic oxidation led to coumestans. This sequence was applied to the formal syntheses of coumestrol and the proposed structure of plicadin as well as total syntheses of flemichapparins B and C.

Chemoselective reduction of quinols as an alternative to Sonogashira coupling: synthesis of polysubstituted benzofurans

An efficient synthetic approach to polysubstituted benzofurans is described, using 2-methoxyquinone as a benzofuran backbone.

Catalytic stereoselective cascade reactions of quinols with trifluoromethyl ketones: direct access to CF3-containing 1,3-dioxolanes

A general and efficient synthesis of CF₃-containing 1,3-dioxolanes using Et₃N-catalyzed ketalization/oxa-Michael cascade of quinols with trifluoromethyl ketones is described. The desired products were obtained in 68%–95% yields with acceptable diastereoselectivities.

Silver-catalysed reactions of alkynes: recent advances

Silver is a less expensive noble metal. Superior alkynophilicity due to π-coordination with the carbon-carbon triple bond makes silver salts ideal catalysts for alkyne-based organic reactions. This review highlights the progress in alkyne chemistry via silver catalysis primarily over the past five years (ca. 2010-2014). The discussion is developed in terms of the bond type formed with the acetylenic carbon (i.e., C-C, C-N, C-O, C-Halo, C-P and C-B). Compared with other coinage metals such as Au and Cu, silver catalysis is frequently observed to be unique. This critical review clearly indicates that silver catalysis provides a significant impetus to the rapid evolution of alkyne-based organic reactions, such as alkynylation, hydrofunctionalization, cycloaddition, cycloisomerization, and cascade reactions.

Re2O7catalyzed dienone-phenol rearrangement

The dienone-phenol rearrangement of 4,4-disubstituted cyclohexadienones to multi-substituted phenols is achieved by employing Re₂O₇as the catalyst.

Palladium-catalyzed α-arylation of aryloxyketones for the synthesis of 2,3-disubstituted benzofurans

A highly efficient palladium-catalyzed α-arylation of aryloxyketones has been developed, allowing for facile installation of various (hetero)aryl groups at C2 position in good to excellent yields. Subsequent cyclodehydration of the resulting α-arylated aryloxyketones provided rapid access to diverse 2,3-disubstitured benzofurans.

Benzofuran derivatives as a novel class of inhibitors of mTOR signaling

High-throughput screening (HTS) hit 1 was previously identified as an inhibitor of the Akt/mTOR (Akt/mammalian target of rapamycin) signaling, which is a major target in oncology. The cytotoxicity of 1 was determined on a panel of human cancer cells lines with an IC₅₀ comprised between 30 and 140 μM. Subsequent structure--activity relationship (SAR) studies led us to the identification of compounds that displayed an enhanced cytotoxicity. We demonstrated also that these molecules directly bind to mTOR complex 1 (mTORC1) and inhibit its kinase activity.

Oxidative spirocyclization of phenolic sulfonamides: scope and applications

A full account of the oxidative dearomatization of para- and ortho-phenolic sulfonamides is provided together with an overview of the chemistry of the products and their elaboration to building blocks for spirocyclic alkaloids. A concise total synthesis of putative lepadiformine complements the discussion.

Silver-catalyzed synthesis of 4-substituted benzofuransvia a cascade oxidative coupling-annulation protocol

A facile synthesis of 4-indole benzofurans via an oxidative dearomatization, a silver-catalyzed cascade Michael addition-annulation, and an aromatization is reported.

Copper-catalyzed synthesis of N-fused heterocycles through regioselective 1,2-aminothiolation of 1,1-dibromoalkenes

The first aminothiolation of 1,1-dibromoalkene is described using an inexpensive copper/N,N-dimethylethylenediamine catalyst. The method provides a powerful means of using easily available 1,1-dihaloalkenes as precursors to fused heterocycles.

Total synthesis of diptoindonesin G via a highly efficient domino cyclodehydration/intramolecular Friedel-Crafts acylation/regioselective demethylation sequence

A highly efficient total synthesis of diptoindonesin G is described employing a domino dehydrative cyclization/intramolecular Friedel-Crafts acylation/regioselective demethylation reaction of aryloxyketone 7 by the action of BCl(3) wherein the tetracyclic 6H-anthra[1,9-bc]furan-6-one skeleton was constructed via the 3-arylbenzofuran in a one-pot manner. This is the first example of the strategic combination of these three reactions in a cascade fashion. The routes presented here allow for direct access to diptoindonesin G and its analogues.