Taming furfuryl cations for the synthesis of privileged structures and novel scaffolds

Synthesis of Oxabicyclo[3.2.1]octan-3-ol Scaffold via Burgess Reagent Mediated Cyclodehydration of δ-Diols under Acidic Conditions

Dehydrative cyclization of δ-diols was achieved by using the Burgess reagent under mild conditions to furnish a novel oxabicyclo[3.2.1]octan-3-ol scaffold. The stereochemistry of the generated oxabicyclic compounds was assigned based on single X-ray crystallography and 2D-NMR experiments.

Alcohols as Substrates in Transition-Metal-Catalyzed Arylation, Alkylation, and Related Reactions

Alcohols are abundant and attractive feedstock molecules for organic synthesis. Many methods for their functionalization require them to first be converted into a more activated derivative, while recent years have seen a vast increase in the number of complexity-building transformations that directly harness unprotected alcohols. This Review discusses how transition metal catalysis can be used toward this goal. These transformations are broadly classified into three categories. Deoxygenative functionalizations, representing derivatization of the C-O bond, enable the alcohol to act as a leaving group toward the formation of new C-C bonds. Etherifications, characterized by derivatization of the O-H bond, represent classical reactivity that has been modernized to include mild reaction conditions, diverse reaction partners, and high selectivities. Lastly, chain functionalization reactions are described, wherein the alcohol group acts as a mediator in formal C-H functionalization reactions of the alkyl backbone. Each of these three classes of transformation will be discussed in context of intermolecular arylation, alkylation, and related reactions, illustrating how catalysis can enable alcohols to be directly harnessed for organic synthesis.

Phosphoric Acid Catalyzed N-Addition/ C-Addition Reaction of 3-Vinyl Indoles with Pyrazole/Pyrazolone to Construct Pyrazole-Substituted 3-(1-Heteroarylethyl)-indole Scaffolds

Developing a highly efficient atom-economic method for the preparation of 3-(1-heteroarylethyl)-indole scaffolds is of significant value in pharmaceutical and agricultural chemistry. Herein, a phosphoric acid-catalyzed N-addition reaction of 3-vinyl indoles with pyrazoles and C-addition reaction of 3-vinyl indoles with pyrazolones were developed. A series of pyrazole-substituted 3-(1-heteroarylethyl)-indole scaffolds were synthesized in excellent yields (up to 99% yield) under mild reaction conditions. A reasonable reaction mechanism was proposed to explain the experimental results.

Dearomative 1,6-addition of P(O)–H to in situ formed p-QM-like ion pairs from 2-benzofuryl-ols to C3-phosphinoyl hydrobenzofurans

We report a dearomative C3-phosphorylation and a tandem C3-phosphorylation/aromatization of 2-benzofuryl-ols with P(O)–H species to afford C3-phosphinoyl hydrobenzofurans and benzofurans, respectively.

Cation Triggered Domino Aza-Piancatelli Rearrangement/Friedel-Crafts Alkylation of Indole-Tethered Furfuyl Alcohols to Access Cycloocta[b]indole Core of Alkaloids

A domino approach to bridged cycloocta[b]indolone through a cascade of aza-Piancatelli rearrangement/Friedel-Crafts alkylation is developed. This transformation has been realized by reaction of an indole-tethered 2-furylcarbinol and substituted aniline in the presence of a Lewis acid to initiate aza-Piancatelli rearrangement followed by an in situ intramolecular Friedel-Crafts alkylation to access bridged tetracyclic frameworks in one pot.

A New Valuable Synthesis of Polyfunctionalized Furans Starting from β-Nitroenones and Active Methylene Compounds

Highly functionalized furans are the key scaffolds of many pharmaceuticals and bioactive natural products. Herein, we disclose a new fruitful synthesis of polyfunctionalized furans starting from β-nitroenones and α-functionalized ketones. The protocol involves two steps promoted by solid supported species, and it provides the title targets from satisfactory to very good overall yields and in an excellent diastereomeric ratios.

Copper-catalyzed tandem annulation/enol nucleophilic addition to access multisubstituted indoles

A method to access various multisubstituted indoles from propargylic alcohols and readily available enol nucleophiles by copper-catalyzed tandem annulation/enol nucleophilic addition has been developed. Compared to the expensive metal catalysts such as platinum, gold, silver, and palladium used previously, the most economical copper(i) catalyst could achieve this reaction efficiently. The fused heterocyclic compounds, pyrrolo[1,2-a] indoles, could be afforded by further transformation of the products. The allyl cation intermediate may be involved in the mechanism.

Catalyst-Controlled Chemodivergent Modification of Indoles with 2-Furylcarbinols: Piancatelli Reaction vs Cross-Dehydrative Coupling Reaction

A divergent synthetic strategy to functionalize the indole nucleus with readily available 2-furylcarbinols was developed. It was found that the 3-(4-oxo-2-cyclopentenyl)indoles were obtained in moderate to good yields (up to 89%) through Piancatelli reaction catalyzed by ZnCl₂, whereas employment of Brønsted acid TFA afforded directly coupled product 3-(2-furyl)indoles in moderate to good yields (up to 87%) via the deprotonation-rearomatization route.

New Furan Derivatives from a Mangrove-Derived Endophytic Fungus Coriolopsis sp. J5

Six new furan derivatives, named 5-(3-methoxy-3-oxopropyl)-furan-2-carboxylic acid (1), 1-(5-(2-hydroxypropanoyl)-furan-2-yl)-pentan-3-one (2), 2-hydroxy-1-(5-(1-hydroxypentyl)-furan-2-yl)-propan-1-one (3), 1-(5-(1,2-dihydroxypropyl)-furan-2-yl)-pentan-1-one (4), 5-(1-hydroxypent-4-en-1-yl)-furan-2-carboxylic acid (5) and 5-(3-hydroxypentyl)-furan-2-carboxylic acid (6), together with two new natural products, named 5-(1-hydroxypentyl)-furan-2-carboxylic acid (7) and (E)-5-(2-carboxyvinyl)-furan-2-carboxylic acid (8), were isolated from the solid rice fermentation of endophytic fungus Coriolopsis sp. J5, which was derived from mangrove plant Ceriops tagal. Their structures were unambiguously elucidated based on 1D and 2D NMR spectroscopy, and by HRESIMS measurements, as well as by comparison with the literature.

An enantioselective organocatalytic intramolecular Morita–Baylis–Hillman (IMBH) reaction of dienones, and elaboration of the IMBH adducts to fluorenones

An efficient synthesis of cyclopenta-fused arenes and heteroarenes has been achieved via an enantioselective organocatalytic intramolecular Morita–Baylis–Hillman (IMBH) reaction of dienones. The IMBH-adducts were transformed to fluorenones in a serendipitous manner.

Sequential aza-Piancatelli rearrangement/Friedel–Crafts alkylation for the synthesis of pyrrolo[1,2-d]benzodiazepine derivatives

2-Furylcarbinols undergo a smooth aza-Piancatelli rearrangement followed by Friedel–Crafts alkylation with (1H-pyrrol-1-yl)aniline, in the presence of In(OTf)₃ at room temperature to afford the corresponding hexahydrobenzo[b]cyclopenta[f]pyrrolo[1,2-d][1,4]diazepin-11(4aH)-one scaffolds.

Dienamine and Friedel-Crafts one-pot synthesis, and antitumor evaluation of diheteroarylalkanals

An asymmetric synthesis of diheteroarylalkanals through one-pot dienamine and Friedel-Crafts reaction is presented. The reaction tolerates a large variety of substituents at different positions of the starting aldehyde and also in the indole nucleophile, and a range of diheterocyclic alkanals can be achieved. Furthermore, we have studied the antiproliferative activity of these new compounds in representative cancer tumor cell lines.

Synthesis of polysubstituted cyclopenta[b]indoles via relay gold(i)/Brønsted acid catalysis

A relay gold(i)/Brønsted acid catalyzed one-pot cyclopentannulation of indoles has been achieved starting from easily accessible 1-(2-aminophenyl)prop-2-ynols and readily available 1,3-dicarbonyls.