A New One-Pot Synthetic Approach to the Highly Functionalized (Z)-2-(Buta-1,3-dienyl)phenols and 2-Methyl-2H-chromenes: Use of Amine, Ruthenium and Base-Catalysis

Base-promoted cyclization of ortho-hydroxyacetophenones with in situ generated cyclopropenes: diastereoselective access to spirobenzo[b]oxepines and related precursors

An unprecedented [5 + 2] spirocyclization route to obtain a vital class of functionalized spirobenzo[b]oxepine-cyclopropanes in good to high yields with excellent diastereoselectivities is reported. This domino reaction proceeds through a regioselective oxa-Michael addition of ortho-hydroxyacetophenones as 1,5-binucleophiles to in situ produced highly reactive cyclopropenes from 2-aroyl-1-chlorocyclopropanecarboxylates triggered by Cs₂CO₃ and the subsequent intramolecular aldol reaction under heating conditions, enabling the formation of new C-O and C-C bonds for benzo[b]oxepine ring synthesis. Moreover, at ambient temperature, the above C-O/C-C bond-forming event takes place preferentially via a [4 + 2] annulation path over a spirocyclization route, leading to substituted fused-cyclopropanes with good diastereoselectivities. Gratifyingly, further alterations of the obtained spirobenzo[b]oxepines and tetrahydrocyclopropa[b]chromenes afford fascinating classes of 4H-chromen-4-ones and cyclopenta[c]chromenes, respectively, under metal-free conditions.

Pd-Catalyzed Alkene Difunctionalization Reactions of Enolates for the Synthesis of Substituted Bicyclic Cyclopentanes

Palladium-catalyzed alkene difunctionalization reactions between alkenes bearing tethered aryl or alkenyl triflates and enolate nucleophiles are described. The transformations form two C-C bonds, a ring, and up to two stereocenters, while producing substituted cyclopentane derivatives that contain appended carbonyl functionality. Products are formed with up to >20:1 diastereoselectivity, and formation of sterically congested bonds between quaternary carbon atoms is feasible.

Rhenium-Catalyzed Regioselective ortho-Alkenylation and [3 + 2 + 1] Cycloaddition of Phenols with Internal Alkynes

An operationally simple and direct rhenium-catalyzed ortho-alkenylation ( C-alkenylation) of unprotected phenols with alkynes was developed. The protocol provided ortho-alkenylphenols exclusively, and formation of para- or multiply alkenylated phenols and hydrophenoxylation ( O-alkenylation) products were not observed. The [3 + 2 + 1] cycloaddition of phenols and two alkynes via ortho-alkenylation was also demonstrated, in which the alkynes functioned as both two- and one-carbon units. These reactions proceeded with readily available starting materials under neutral conditions without additional ligands.

Visible-Light-Induced External Radical-Triggered Annulation To Access CF2-Containing Benzoxepine Derivatives

A facile and diversified synthesis of functionalized CF₂-containing benzoxepine derivatives via photoredox catalysis was achieved in this work. This novel protocol features broad substrate scope, mild reaction conditions, operational simplicity, easy scale-up, and versatile derivatization, which would facilitate its practical and broad applications in the construction of valuable and synthetically challenging heterocycles.

FeCl3 catalysed 7-membered ring formation in a single pot: a new route to indole-fused oxepines/azepines and their cytotoxic activity

FeCl₃ catalysed construction of 7 membered ring, oxepine and azepine derivatives by the reaction of 2,3-dichloro N-heterocycles with 2-(1H-indol-2-yl)phenol/aniline. Several of these compounds were found anti-proliferative properties against cancer cell lines.

Base-Promoted Formal [4 + 3] Annulation between 2-Fluorophenylacetylenes and Ketones: A Route to Benzoxepines

The first base-promoted formal [4 + 3] annulation between 2-fluorophenylacetylenes and ketones has been disclosed. The reaction proceeds through a tandem α-vinylation of ketones followed by an intramolecular nucleophilic aromatic substitution (SNAr) reaction of the in situ generated β,γ-unsaturated ketone intermediates, providing a straightforward access to a wide range of functionalized benzoxepines in moderate to high yields. The transition-metal-free methodology featured a wide substrate scope, the use of easily available starting materials, and a high functional group tolerance.

Rhodium-catalyzed (5+1) annulations between 2-alkenylphenols and allenes: a practical entry to 2,2-disubstituted 2H-chromenes

Readily available alkenylphenols react with allenes under rhodium catalysis to provide valuable 2,2-disubstituted 2H-chromenes. The whole process, which involves the cleavage of one C-H bond of the alkenyl moiety and the participation of the allene as a one-carbon cycloaddition partner, can be considered a simple, versatile, and atom-economical (5+1) heteroannulation. The reaction tolerates a broad range of substituents both in the alkenylphenol and in the allene, and most probably proceeds through a mechanism involving a rhodium-catalyzed C-C coupling followed by two sequential pericyclic processes.

High-yielding sequential one-pot synthesis of chiral and achiral α-substituted acrylates via a metal-free reductive coupling reaction

A general process for the high-yielding synthesis of substituted chiral and achiral α-substituted acrylates was achieved through the sequential one-pot combination of a metal-free reductive coupling reaction followed by an Eschenmoser methylenation. The proline catalyzed reaction of Meldrum's acid, aldehydes and Hantzsch ester followed by methylenation was successful with Eschenmoser's salt in the presence of an alcohol solvent. Herein, we have shown the high-yielding synthesis of privileged building blocks from chiral/achiral α-substituted acrylates and shown them to be very good intermediates in the pharmaceuticals and natural products synthesis.

Kinetic resolution in asymmetric epoxidation using iminium salt catalysis

The first reported examples of kinetic resolution in epoxidation reactions using iminium salt catalysis are described, providing up to 99% ee in the epoxidation of racemic cis-chromenes.

Hexatriene Formation from the Regiospecific Alkene Cross-Metathesis of Trans-1-(Buta-1,3-Dien-1-yl)-2-Acryloyloxynaphthalene

Wittig olefination of 2-hydroxy-1-naphthaldehyde with allylidenetriphenylphosphorane afforded trans-1-(buta-1,3-dien-1-yl)-2-naphthol in good yield. Subsequent O-acylation with acryloyl chloride provided the corresponding acrylate ester. Attempts to effect cyclisation of the latter by ring-closing metathesis with Grubbs’ 2nd generation catalyst failed to provide 5H-naphth[2,1-b]oxocin-5-one and instead induced a novel cross-metathesis reaction to generate trans,trans,trans-1,6-bis(2-acryloyloxynaphthalen-1-yl)hexa-1,3,5-triene, the structure of which was established by 1H NMR spectroscopy and by X-ray crystallography.

Optimization of the ultrasound-assisted synthesis of allyl 1-naphthyl ether using response surface methodology

Allyl 1-naphthyl ethers are useful compounds for different purposes, but reported methods to synthesize them require long reaction times. In this work, we have obtained allyl 1-naphthyl ether in good yield using ultrasonic-assisted methodology in a 1-h reaction. A central composite design was used to obtain a statistical model and a response surface (p<0.05; R(2)=0.970; R(2)(adj)=0.949; R(2)(pred)=0.818) that can predict the optimal conditions to maximize the yield, validated experimentally.

Sequential one-pot combination of multi-component and multi-catalysis cascade reactions: an emerging technology in organic synthesis

Creating sequential one-pot combinations of multi-component reactions (MCRs) and multi-catalysis cascade (MCC) reactions is a challenging task that has already emerged as a new technology in synthetic organic chemistry. Through one-pot sequential combination of MCRs/MCC reactions, the chemical products (fine chemicals, agrochemicals and pharmaceuticals) that add value to our lives can be produced with less waste and greater economic benefits. Within this Emerging Area, we describe our recent developments and designs for sequential one-pot MCRs/MCC reactions to facilitate their realization as biomimetics in organic chemistry.