Copper-Catalyzed Synthesis of Substituted Furans and Pyrroles by Heterocyclodehydration and Tandem Heterocyclodehydration–Hydration of 3-Yne-1,2-diols and 1-Amino-3-yn-2-ol Derivatives

One-pot furan synthesis through diethylzinc-mediated coupling reaction between two α-bromocarbonyl compounds

Polysubstituted furans were synthesized in one-pot through the Et2Zn-mediated coupling reaction between dibromoketones and monobromo carbonyl compounds and the subsequent β-elimination with bromoacetyl bromide. Polysubstituted pyrroles were also prepared in one-pot by addition of primary amines after the coupling reaction.

Zr-Catalyzed Synthesis of Tetrasubstituted 1,3-Diacylpyrroles from N-Acyl α-Aminoaldehydes and 1,3-Dicarbonyls

A Zr-catalyzed synthesis of tetrasubstituted 1,3-diacylpyrroles is reported that employs the direct use of N-acyl α-aminoaldehydes with 1,3-dicarbonyl compounds. The products were formed in up to 88% yield and shown to be hydrolytically and configurationally stable under the reaction conditions (THF/1,4-dioxane and H₂O). The N-acyl α-aminoaldehydes were readily prepared from the corresponding α-amino acids. The reaction tolerates a wide array of substrate types including alkyl-, aryl-, heteroaryl-, and heteroatom-containing groups on the aminoaldehyde side chain. A variety of 1,3-dicarbonyls proved amenable to the reaction along with an aldehyde derived from a l,l-dipeptide, an aldehyde generated in situ, and an N-acylated glucosamine.

A Central-to-Axial Chirality Conversion Strategy for the Synthesis of C-N Axially Chiral N-Arylpyrroles

We present a central-to-axial chirality conversion strategy for the construction of C-N axially chiral N-arylpyrroles via a gold(I)-catalyzed 5-endo-dig cyclization/dehydration cascade from amino acid derivatives. The reaction exhibits high efficiency on the central-to-axial chirality conversion. Density functional theory calculations suggest that the stereospecificity during the central-to-axial chirality conversion lies in the stability of the conformations of the amino alcohol and the corresponding low barrier transition state.

Ready Access to Densely Substituted Furans Using Tsuji-Wacker-Type Cyclization

A competent method for the construction of highly substituted furans catalyzed by Pd(II) and Cu(II) chloride has been developed. The method provides easy access to di-, tri-, and tetrasubstituted furans from corresponding diols with relatively mild conditions in a unified strategy. The developed method has been successfully tested with more than 25 substrates, which resulted in furans of multiple substitution patterns with up to 84% isolated yields.

Click Nucleophilic Conjugate Additions to Activated Alkynes: Exploring Thiol-yne, Amino-yne, and Hydroxyl-yne Reactions from (Bio)Organic to Polymer Chemistry

The 1,4-conjugate addition reaction between activated alkynes or acetylenic Michael acceptors and nucleophiles (i.e., the nucleophilic Michael reaction) is a historically useful organic transformation. Despite its general utility, the efficiency and outcomes can vary widely and are often closely dependent upon specific reaction conditions. Nevertheless, with improvements in reaction design, including catalyst development and an expansion of the substrate scope to feature more electrophilic alkynes, many examples now present with features that are congruent with Click chemistry. Although several nucleophilic species can participate in these conjugate additions, ubiquitous nucleophiles such as thiols, amines, and alcohols are commonly employed and, consequently, among the most well developed. For many years, these conjugate additions were largely relegated to organic chemistry, but in the last few decades their use has expanded into other spheres such as bioorganic chemistry and polymer chemistry. Within these fields, they have been particularly useful for bioconjugation reactions and step-growth polymerizations, respectively, due to their excellent efficiency, orthogonality, and ambient reactivity. The reaction is expected to feature in increasingly divergent application settings as it continues to emerge as a Click reaction.

Synthesis of 2,3-Ring Fused Pyrroles via Cu-Catalyzed 5-exo-dig Annulation of Alkyne-Tethered Enaminones

A copper-catalyzed annulation of alkyne-tethered enaminones for the synthesis of 2,3-ring fused pyrroles is reported. The 5-exo-dig cyclization/olefin migration reaction delivers the multisubstituted pyrroles in 59-99% yields with 16 examples. This strategy features easily available starting materials, mild reaction conditions, and a cheap ligand-free copper catalyst. The atom-economic transformation provides a simple access to a variety of synthetic useful pyrroles and their derivatives.

Access to Benzylic Quaternary Carbons from Aromatic Ketones

The construction of benzylic all-carbon quaternary stereocenters, which are ubiquitous in biomolecules and drugs, is a task of high practical significance. Herein, we disclose a highly efficient one-pot method of constructing all-carbon quaternary structural units from aryl ketones, revealing that the entire process involves three consecutive chemical events, namely nucleophilic addition, Meinwald 1,2-hydrogen migration, and alkylation. Interestingly, dimerization of acetophenones results in formation of 2,4-diarylfurans under the employed conditions rather than the quaternary carbon products.

Synthetic Studies toward (±)-Furanocembranoid 1: Construction of the Acyclic Carbon Framework

Herein, we report the synthesis of the entire acyclic carbon framework toward (±)-furanocembranoid 1 via the longest linear sequence of 12 steps from commercially available linalool and diethyl 2-isopropylmalonate. Key to the success of this synthetic approach is a silver-catalyzed enyne-annulation reaction for the formation of 2,4-disubstituted furan motif of unique furanocembranoid 1, isolated from Croton oblongifolius. Construction of macrocycle has also been explored using the ring-closing metathesis reaction.

Cu(OAc)2 /TEMPO Cooperative Promoted Hydroamination Cyclization and Oxidative Dehydrogenation Cascade Reaction of Homopropargylic Amines

A novel and efficient Cu(OAc)₂ -catalyzed hydroamination cyclization and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidative dehydrogenation cascade reaction of homopropargylic amines has been developed. A library of 1,2-disubstituted pyrrole derivatives were obtained in good-to-high yields in one pot with no step-by-step feeding process. This reaction involved TEMPO playing dual roles as both an oxidative dehydrogenation reagent and a ligand. An insight into the reaction mechanism was obtained by using several analytical determination methods.

Hypervalent iodine-triggered transformation of homopropargyl sulfonamides into dihalo-2,3-dihydropyrroles

A novel hypervalent iodine-triggered hydroamination of homopropargyl sulfonamides with copper halides to obtain dihalo-2,3-dihydropyrroles was efficiently developed.

Recent developments in the group-1B-metal-catalyzed synthesis of pyrroles

Pyrroles are important synthetic targets as a result of their occurrence in numerous biologically active molecules, their important roles in diverse living processes, and their utility as versatile intermediates.

Pyrrole: a resourceful small molecule in key medicinal hetero-aromatics

Pyrrole is widely known as a biologically active scaffold which possesses a diverse nature of activities.

Expedient synthesis of tetrasubstituted pyrroles via a copper-catalyzed cascade inter-/intramolecular cyclization of 1,3-enynes carry a nitro group with amines

Various tetrasubstituted pyrroles/pyrazoles have been prepared from nitro-substituted 1,3-enynes with aromatic amines/hydrazinesviaa copper-catalyzed cascade aza-Michael addition, cyclization and aromatization.

Gold-catalyzed cascade C–H/C–H cross-coupling/cyclization/alkynylation: an efficient access to 3-alkynylpyrroles

An efficient approach to 3-alkynylpyrroles has been developed through the gold-catalyzed cascade oxidative C–H/C–H cross-coupling, cyclization and in situ oxidative alkynylation.

A [3 + 2]-annulation approach to tetrasubstituted furans from MBH-carbonates of acetylenic aldehydes via sequential substitution/cycloisomerization

A new organo base-mediated cascade reaction has been developed for the synthesis of uniquely substituted tetrasubstituted furans, 2-furan-3-yl acrylates, starting from MBH-carbonates of acetylenic aldehydes and keto-methylenes.

Synthesis of pandamarilactone-1

The first total synthesis of pandamarilactone-1, an alkaloid of Pandanus amaryllifolius, is reported. The nine-step synthesis features furan oxidation with singlet oxygen and then spiro-N,O-acetalization and elimination to generate the natural product and further Pandanus alkaloids, pandamarilactonines A-D.

One-pot synthesis of polysubstituted 3-acylpyrroles by cooperative catalysis

Polysubstituted 3-acylpyrroles were synthesized from readily available unsaturated ketones and N-substituted propargylated amines via an aza-Michael/alkyne carbocyclization cascade followed by oxidation in one pot.

A recyclable palladium-catalyzed synthesis of 2-methylene-2,3-dihydrobenzofuran-3-ols by cycloisomerization of 2-(1-hydroxyprop-2-ynyl)phenols in ionic liquids

A recyclable palladium-catalyzed synthesis of 2-methylene-2,3-dihydrobenzofuran-3-ols 2 by heterocyclization of 2-(1-hydroxyprop-2-ynyl)phenols 1 in an ionic liquid medium (BmimBF4) is presented. The process takes place under relatively mild conditions (100 °C, 5 h) in the presence of catalytic amounts (2 mol %) of PdI2 in conjunction with KI (5 equiv with respect to PdI2) and an organic base, such as morpholine (1 equiv with respect to 1), to give 2 in high yields (70%-86%). The PdI2-KI catalytic system could be recycled up to six times without appreciable loss of activity. Moreover, products 2 could be easily converted in a one-pot fashion into 2-hydroxymethylbenzofurans 3 (52%-71%, based on 1) and 2-methoxymethylbenzofurans 4 (52%-80%, based on 1) by acid-catalyzed allylic isomerization or allylic nucleophilic substitution.