Rhodium-Catalyzed Intramolecular Difluoromethylenative Dearomatization of Phenols

NHC catalyzed radical tandem cyclization: an efficient synthesis of α,α-difluoro-γ-lactam derivatives

Herein, an N-heterocyclic carbene (NHC) catalyzed radical tandem cyclization reaction of N-allylbromodifluoroacetamides and aldehydes has been developed. This method is an efficient protocol for synthesizing α,α-difluoro-γ-lactam derivatives in moderate to good yields (27 examples, up to 88% yield and 10 : 1 dr). This strategy features mild and metal-free conditions, high efficiency, and a broad substrate scope.

Highly Diastereoselective [3 + 2] Cycloaddition of Aziridines with Difluorinated Silyl Enol Ethers: Divergent Synthesis of 4,4-Difluoropyrrolidines and 4-Fluoropyrroles

A highly diastereoselective [3 + 2] cycloaddition of aziridines with difluorinated silyl enol ethers has been developed. This approach provides a facile methodology for highly functionalized gem-difluorinated pyrrolidines in good to excellent yields with good functional group tolerance. A one-pot, two-step approach for synthesis of structurally interesting fluorinated pyrroles has also been developed through a cycloaddition/aromatization/desulfonation sequence. Moreover, readily available substrates, mild reaction conditions, and easy scale-up synthesis show practical advantages.

Electrophilic Halospirocyclization of N-Benzylacrylamides to Access 4-Halomethyl-2-azaspiro[4.5]decanes

An electrophilic spirocyclization of N-benzylacrylamides with N-halosuccinimides (NXS) as the halogenating reagents has been developed. This reaction is carried out at room temperature under simple conditions without relying on metal reagents, photochemistry, or electrochemistry, providing a fast and efficient route to synthesize a wide variety of 4-halomethyl-2-azaspiro[4.5]decanes with satisfactory yields. The approach is further highlighted through gram-scale synthesis and diverse transformations of the spiro products.

Pd-Catalyzed Asymmetric Annulative Dearomatization of Phenols for Regio- and Enantioselective Synthesis of Spirocyclohexadienones

A palladium-catalyzed asymmetric annulative dearomatization of phenols with butene dicarbonate is reported, enabling twofold decarboxylative allylation to regioselectively produce a range of spirocyclohexadienones with 29-95% yields and 74-99% ee. A catalytic dearomative formal [4 + 2] cyclization of 1,1'-biphenyl-2,4'-diols delivered spiro[chromane-4,1'-cyclohexane]-2',5'-dien-4'-ones with high enantioselectivity, whereas enantioenriched spiro[cyclohexane-1,4'-quinoline]-2,5-dien-4-ones were generated starting from 2'-amino-[1,1'-biphenyl]-4-ols as 1,4-dinucleophiles.

Redox-Neutral Intramolecular Dearomative Spirocyclization of Phenols Induced by Visible Light

Described herein is a redox-neutral intramolecular dearomative spirocyclization induced by visible light. The photochemical cyclization was catalyzed by a phenolate anion-derived photocatalyst and delivered the spirocyclohexadienone. Mechanistic experiments revealed that the aryl halide was reduced to aryl radical via the single-electron transfer (SET) process under visible light irradiation. The electrophilic addition of an aryl radical with the phenolate anion moiety gave a radical anion intermediate, which recycled the photocatalyst by a second SET process.

Photomediated Spirocyclization of N-Benzyl Propiolamide with N-Iodosuccinimide for Access to Azaspiro[4.5]deca-6,9-diene-3,8-dione

A metal- and oxidant-free route for affording azaspiro[4.5]deca-6,9-diene-3,8-dione via photomediated iodinated spirocyclization of N-(4-methoxybenzyl) propiolamide has been developed. The reaction underwent a radical addition/ipso-cyclization/dearomatization process at room temperature and successfully constructed C-C and C-I bonds. This green and convenient approach could be generally expanded to produce a range of iodinated spirocyclization products in moderate to good yields.

Divergent Synthesis of gem-Difluorinated Oxa-Spirocyclohexadienones by One-Pot Sequential Reactions of p-Hydroxybenzyl Alcohols with Difluoroenoxysilanes

A new efficient formal [2 + 3] cyclization of p-hydroxybenzyl alcohols with difluoroenoxysilanes has been established. This convenient one-pot sequential procedure enables the divergent construction of highly functionalized gem-difluorinated oxa-spirocyclohexadienones under mild conditions. As opposed to the common C1 synthons in previous studies, difluoroenoxysilanes acted as new 3-atom (CCO) synthons for the first time here. The AcOH and H₂O generated in the reaction are critical for the reactions to proceed smoothly.

Synthetic methods for compounds containing fluoro-lactam units

In recent years, considerable attention has been devoted to the exploration of novel synthetic methods for fluoro-lactams due to their significant biological and pharmaceutical activities. This review summarizes recently established strategies for synthesizing fluorine-substituted lactams, including fluoro-β-lactams, fluoro-γ-lactams, and fluoro-δ-lactams. Additionally, the reaction scopes, limitations, and mechanisms are discussed.

meta-Selective C–H difluoromethylation of various arenes with a versatile ruthenium catalyst

A ruthenium-enabled meta-selective C–H difluoromethylation of arenes has been developed.

“A Jack of Trio”-robust one-pot metal free oxidative amination, azidation and peroxidation of phenols

Facile generation of quaternary carbon centres has been realised in the presence of phenyl trimethyl ammonium tribromide (PTAB) mediated oxidative dearomatisation.

Copper-catalyzed gem-difluoromethylenation of C(sp2)–H bonds of alkenes

Copper-catalyzed gem-difluoromethylenation of the C(sp²)–H bonds of alkenes has been developed. This protocol is the first to efficiently achieve gem-difluoromethylenation of C(sp²)–H bonds of unactivated aliphatic terminal olefins and is applied in gem-difluoromethylenation/cyclization of alkenes.

Visible light-induced intramolecular dearomative cyclization of α-bromo-N-benzyl-alkylamides: efficient construction of 2-azaspiro[4.5]decanes

An efficient intramolecular dearomative cyclization via visible light-induced photoredox catalysis allows for a highly regioselective dearomative cyclization of α-bromo-N-benzyl-alkylamides to construct 2-azaspiro[4.5]decanes in the presence of an iridium catalyst.

PhSeBr mediated hydroxylative oxidative dearomatization of naphthols – an open air facile one-pot synthesis of ketols

A facile open air methodology for oxidative dearomatisation of planar naphthols is described.

Phenyl trimethyl ammonium tribromide mediated robust one-pot synthesis of spiro-oxacycles – an economic route – stereoselective synthesis of oxaspirohexacyclodieneones

This paper entails the first recognition of Phenyl Trimethyl Ammonium Tribromide (PTAB) as an effective reagent for spiro-cyclizations proceeding via oxidative dearomatization.