Iodocyclization of N-Arylpropynamides Mediated by Hypervalent Iodine Reagent: Divergent Synthesis of Iodinated Quinolin-2-ones and Spiro[4,5]trienones

A General and Highly Versatile Heterogeneous Pd-Catalyzed Oxidative Aminocarbonylation of Alkynes with Aromatic and Aliphatic Amines

An efficient heterogeneous catalytic system for the oxidative aminocarbonylation of alkynes and amines in the presence of CO/O2 to afford substituted propiolamides has been developed. The active nanocatalyst, [Pd/Mg3Al-LDH]-300(D), is composed by Pd nanoaggregates (2-3 nm average particle size) stabilized over a partially dehydrated [Mg3Al-LDH] matrix. The methodology has resulted widely applicable, being the first catalytic system, either homogeneous or heterogeneous, able to activate not only aliphatic amines but also poorly-nucleophilic aromatic amines. In fact, >60 substituted propiolamides have been synthesized in good to excellent isolated yields through this methodology, being 27 novel compounds. An important characterization effort (XRD, 27Al MAS NMR, TGA, TPD-CO2, BET area, XPS, HAADF-HRSTEM and HRTEM) and optimization of the synthesis conditions of the optimal catalyst has been performed. This study, together with a series of kinetic and mechanistic essays, indicates that the optimal catalyst is composed by Pd(0) species stabilized in a partially dehydrated/dehydroxylated LDH material with a Mg/Al molar ratio of 3 and a small crystallite size. All the experimental data indicates that the in situ formation of [PdI2] active species in the material surface together with the presence of a matrix with the optimal acid/base properties are key aspects of this process.

Oxidative Cascade Iodocyclization of 1,n-Dienes: Synthesis of Iodinated Benzo[b]azepine and Benzo[b]azocine Derivatives

An oxidative cascade iodocyclization of 1,7- or 1,8-dienes has been realized under mild conditions. By employing I2 as an iodine source, this protocol provides a concise and efficient approach to a great deal of biologically significant iodinated benzo[b]azepine and benzo[b]azocine derivatives in moderate to good yields. The gram-scale synthesis and further transformation of products render the approach practical and attractive. Radical trapping and deuterium-labeling experiments help to understand the mechanism.

Radical Three-Component Nitro Spiro-Cyclization of Unsaturated Sulfonamides/Amides to Access NO2-Featured 4-Azaspiro[4.5]decanes

Free radical three-component nitration/spirocyclization of unsaturated sulfonamides/amides with tert-butyl nitrite was developed for the construction of diverse NO2-revised 4-azaspiro[4.5]decanes. This tandem system featured metal-free participation, simple operation, good selectivity/yields, and a green/low-cost O source. Meanwhile, one nitro-containing complex molecule and a scaled-up operation were performed well to test the synthetic potential of the cascade reaction. Isotopic labeling, radical inhibition experiments, and DFT analysis were carried out to gain insight into the reaction process.

Fluoride-Catalyzed Cross-Coupling of Carbamoyl Fluorides and Alkynylsilanes

We report the synthesis of alkynamides via the cross-coupling of carbamoyl fluorides and alkynylsilanes catalyzed by tetrabutylammonium fluoride (TBAF). In contrast to previously reported transformations of carbamoyl fluorides, C-F bond cleavage is achieved under exceptionally mild conditions (room temperature, low catalyst loadings, and short reaction times) without the need for strongly nucleophilic reagents and/or catalysts. This method offers distinct advantages over transition-metal-catalyzed approaches, such as tolerance to aryl halide moieties and complementary chemoselectivity.

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.

Nitro-Spirocyclization of Biaryl Ynones with tert-Butyl Nitrite: Access to NO2-Substituted Spiro[5,5]trienones

A metal/peroxide-free involved simple cascade 6-exo-trig spirocyclization of tert-butyl nitrite with biaryl ynones has been finished, which resulted in various NO₂-modified spiro[5,5]trienones with good regioselectivity/yields. A variety of scaled-up experiments, reduction/epoxidation operations, and mechanistic studies were performed to verify the merits and spirocyclization process of this radical system. Finally, the structure of the spirocycles was confirmed by single-crystal X-ray diffraction.

K2S2O8-Mediated Radical Cyclization of 1,6-Enyne for the Synthesis of Diiodonated γ-Lactams

A novel and convenient K₂S₂O₈-mediated diiodo cyclization of 1,6-enynes for the facile synthesis of functionalized γ-lactam derivatives has been developed. This reaction features mild and transition-metal-free conditions, which offer a green and efficient entry to synthetically important γ-lactam scaffolds. Mechanistic studies suggest that iodide radicals initiate the cascade cyclic transformation.

Synthesis of 3-Haloindoles via Cascade Oxidative Cyclization/Halogenation of 2-Alkenylanilines Mediated by PIDA and LiBr/KI

The treatment of 2-alkenylanilines with phenyliodine(III) diacetate (PIDA) and LiBr or KI in HFIP was found to afford the corresponding 3-haloindoles via cascade oxidative cyclization/halogenation encompassing oxidative C-N/C-X (X = Br, I) bond formations. A plausible mechanism involving the in situ formation of the reactive AcO-X (X = Br, I) from the reaction of PIDA and LiBr/KI was postulated.

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.

Regiodivergent C-N Coupling of Quinazolinones Controlled by the Dipole Moments of Tautomers

Herein, we report that the dipole moments of tautomers can be the controlling factor for regiodivergent synthesis of either 14H-quinazolino[3,2-f]phenanthridin-14-ones or 6H-quinazolino[1,2-f]phenanthridin-6-ones, selectively, from unmasked 2-([1,1'-biphenyl]-2-yl)quinazolin-4(3H)-one. An intramolecular C(sp²)-NH coupling reaction mediated by PhI(OCOOCF₃)₂ could lead to two different regioisomers selectively at different temperatures when the dielectric constants of solvents like hexafluoroisopropanol and trifluoroacetic acid matched with the tautomer's dipole moments.

Asymmetric Synthesis of Propargylic α-Stereogenic Tertiary Amines by Reductive Alkynylation of Tertiary Amides Using Ir/Cu Tandem Catalysis

The development of an asymmetric protocol for the reductive alkynylation of amides to access important α-stereogenic tertiary propargylic amines is reported using a tandem Ir-catalyzed hydrosilylation/enantioselective Cu-catalyzed alkynylation. The reaction utilizes a Cu/PyBox catalyst system in the alkynylation step to achieve asymmetry and affords excellent yields with moderate to good levels of enantiocontrol while employing low Ir-catalyst loadings (0.5 mol %).

Alkylation/Ipso-cyclization of Active Alkynes Leading to 3-Alkylated Aza- and Oxa-spiro[4,5]-trienones

A method for the preparation of 3-alkylated spiro[4.5]trienones via alkylation/ipso-cyclization of activated alkynes with 4-alkyl-DHPs under transition-metal-free conditions is proposed. This alkylation successively undergoes the generation of alkyl radicals, addition of alkyl radicals to the alkynes, and intramolecular ipso-cyclization. The mechanism studies suggest that the alkylation/ipso-cyclization involves a radical process. This ipso-cyclization procedure shows a series of advantages, such as accessibility, mild conditions, high efficiency, greater safety, and an environmentally friendly method.

Tandem trifluoromethylthiolation and cyclization of N-aryl-3-butenamides with AgSCF3: divergent access to CF3S-substituted 3,4-dihydroquinolin-2-ones and azaspiro[4,5]dienones

A AgSCF3-mediated tandem trifluoromethylthiolaton and cyclization of N-aryl-3-butenamides was developed. It showed divergent reactivities and enabled the selective syntheses of CF3S-substituted 3,4-dihydroquinolin-2-ones and azaspiro[4,5]dienones. The selectivity was achieved through different...

Visible Light-Promoted Selenylative Spirocyclization of Biaryl Ynones toward the Formation of Selenated Spiro[5.5]trienones

A visible-light induced dearomative cascade cyclization of biaryl ynones with diselenides under photocatalyst and external additive-free conditions has been explored, giving a series of selenated spiro[5.5]trienones in moderate to good...

Remote difunctionalization of 2H-indazoles using Koser's reagents

A new, efficient, and metal-free protocol has been developed for remote difunctionalization of unreactive C-H bonds at the benzene core of 2H-indazole by employing Koser's reagents, which act as both sulfonyloxylating and iodinating agents under ambient air. The present methodology represents facile access to C-4-sulfonyloxylated and C-7-iodinated 2H-indazole derivatives with high regioselectivity, wide functional group tolerance, and broad substrate scope in good to excellent yields. The formed 4,7 disubstituted 2H-indazoles are the precursors of various C-4,7-functionalized 2H-indazoles through simple transformations.

Palladium-catalyzed difunctionalization/dearomatization of N-benzylacrylamides with α-carbonyl alkyl bromides: facile access to azaspirocyclohexadienones

An efficient palladium-catalyzed difunctionalization/dearomatization of N-benzylacrylamides with α-carbonyl alkyl bromides as alkyl radical precursors has been described. Various α-carbonyl alkyl bromides, including α-bromoalkyl esters and ketones, reacted smoothly to provide important azaspirocyclohexadienones in moderate to excellent yields. In addition, mechanistic studies suggested that the reaction proceeded via a radical pathway.

Unexpected Substituent Effects in Spiro-Compound Formation: Steering N-Aryl Propynamides and DMSO toward Site-Specific Sulfination in Quinolin-2-ones or Spiro[4,5]trienones

A highly substituent-dependent rearrangement allows for the novel and SOCl₂-induced divergent synthesis of 3-methylthioquinolin-2-ones and 3-methylthiospiro[4.5]trienones through intramolecular electrophilic cyclization of N-aryl propyamides. DMSO acts as both solvent and sulfur source, and use of DMSO-h₆/d₆ enables the incorporation of SCH₃ or SCD₃ moieties to the 3-position of the heterocyclic framework. Different para-substituents trigger divergent reaction pathways leading to the formation of quinolin-2-ones for mild substituents and spiro[4,5]trienones for both electron-withdrawing and -donating substituents, respectively. On the basis of both computational and experimental results, a new mechanism has been put forward that accounts for the exclusive spirolization/defluorination process and the surprising substituent effects.

Radical bromination-induced ipso cyclization-ortho cyclization sequence of N-hydroxylethyl-N-arylpropiolamides

A facile procedure is reported for the synthesis of various 2-bromo-1-phenyl-5,6-dihydro-3H,7aH-benzo[b]pyrrolo[2,1-c][1,4]oxazin-3-ones via a radical bromination-induced ipso cyclization-ortho cyclization sequence of N-arylpropiolamides in the presence of TBAB and oxone. The radical cyclization sequence involves a radical bromo α-addition into the alkyne, ipso-cyclization, and ortho-trapping of the spirocyclic intermediate.

Strategies and methodologies for the construction of spiro-γ-lactams: an update

This review gives an insight into the most recent synthetic methodologies towards spiro-γ-lactams, a class of compounds that are present in a wide range of synthetic bioactive and naturally occurring molecules.

Selenocysteinyl electrophiles efficiently promote the formation of coumarin and quinolinone cores by 6-endo-dig cyclization

Efficient methods have been disclosed for the construction of nitrogen and oxygen containing heterocyclic systems attached to selenocysteine or selenoglutathione.

Photo-mediated synthesis of halogenated spiro[4,5]trienones of N-aryl alkynamides with PhI(OCOCF3)2 and KBr/KCl

A novel and convenient photo-mediated halogenated spirocyclization of N-(p-methoxyaryl)propiolamides has been developed. The photolysis of phenyliodine bis(trifluoroacetate) (PIFA) as an iodination reagent led to iodinated ipso-cyclization under the irradiation of a xenon lamp, while brominated ipso-cyclization or chlorinated ipso-cyclization was achieved by irradiating a mixture of PIFA and KBr/KCl under a blue LED. The present protocol simply utilizes light as the safe and clean energy source and doesn't require any external photocatalyst providing various 3-halospiro[4,5]trienones in good to excellent yields (up to 93%).

Convenient Synthesis of 6,7,12,13-Tetrahydro-5H-Cyclohepta[2,1-b:3,4-b']diindole Derivatives Mediated by Hypervalent Iodine (III) Reagent

Bisindolyl alkaloids represent a large family of natural and synthetic products that display various biological activities. Among the bisindole compounds, 6,7,12,13-tetrahydro-5H-cyclohepta[2,1-b:3,4-b']diindoles have received little attention. Only two methods have been developed for the construction of the 6,7,12,13-tetrahydro-5H-cyclohepta[2,1-b:3,4-b']diindole scaffold thus far, including the classical Fischer indole synthesis conducted by reacting indole-fused cycloheptanone and hydrazines, and the condensation reaction to build the seven-membered ring. Here, we report for the first time a new route to synthesize 6,7,12,13-tetrahydro-5H-cyclohepta[2,1-b:3,4-b']diindoles through intramolecular oxidative coupling of 1,3-di(1H-indol-3-yl)propanes in the presence of PIFA, DDQ and TMSCl with moderate to excellent yields.

Synthesis and Configuration of Natural Dracaenones

Several dracaenones were synthesized in enantiopure forms for the first time. The key chiral center at C-7 was installed with well-defined stereochemistry using either an Evans aldol condensation or a chiral oxidant-mediated asymmetric epoxidation, while and the critical oxidative coupling was achieved under the PIFA/PTA conditions. Comparison of optical rotations for the synthetic and natural samples allowed for unequivocal assignment of the absolute configurations of the natural dracaenones.

Metal-free switchable ortho/ipso-cyclization of N-aryl alkynamides: divergent synthesis of 3-selenyl quinolin-2-ones and azaspiro[4,5]trienones

A selenium radical triggered switchable ortho/ipso-cyclization cascade of N-aryl alkynamides has been devised under metal-free conditions to access 3-selenyl quinolin-2-ones and 3-selenospiro[4,5]trienones in high yields (up to 98%).

Hypervalent iodine reactions utilized in carbon–carbon bond formations

This review covers recent developments of hypervalent iodine chemistry in dearomatizations, radicals, hypervalent iodine-guided electrophilic substitution, arylations, photoredox, and more.

Regioselective radical arylation: silver-mediated synthesis of 3-phosphorylated coumarins, quinolin-2(1H)-one and benzophosphole oxides

A silver-mediated domino radical addition/cyclization reaction of diaryl- or dialkyl-phosphine oxides with propynoic acid derivatives delivering 3-phosphorylated coumarins, quinolin-2(1H)-one and benzophosphole oxides is presented.

Visible-light promoted one-pot synthesis of sulfonated spiro[4,5]trienones from propiolamides, anilines and sulfur dioxide under transition metal-free conditions

A novel visible-light promoted sulfonylation/ipso-cyclization of N-arylpropiolamides with aromatic amines and DABCO·(SO₂)₂ to synthesize various sulfonated spiro[4,5]trienones is reported.

ZnBr2/Oxone-mediated ipso-cyclization of N-(3-phenylprop-2-yn-1-yl)aniline

1-Azaspiro[4.5]deca-3,6,9-trien-8-ones have been selectively synthesized from N-tosyl-N-(prop-2-yn-1-yl)anilines via a ZnBr₂/Oxone-mediated radical ipso-cyclization pathway.

Nitration and Cyclization of Arene-Alkynes: An Access to 9-Nitrophenathrenes

A nitration and cyclization of arene-alkynes has been developed, affording 9-nitrophenathrenes efficiently. This reaction probably proceeds via addition of the nitrogen dioxide to the alkyne moiety, intramolecular radical addition of vinyl radical to one aryl ring, oxidation of radical intermediate into carbocation species, and elimination of a proton. In this transformation, Fe(NO₃)₃ was used as both nitro source and oxidant.

Synthesis of Difluoromethylated and Phosphorated Spiro[5.5]trienones via Dearomative Spirocyclization of Biaryl Ynones

Copper- or silver-catalyzed cascade radical addition/dearomative spirocyclization of biaryl ynones with fluoroalkyl bromides or diethylphosphite has been realized for the first time. This method provides a novel and step-economical protocol for the divergent synthesis of a wide range of difluoromethylated or monofluoromethylated and phosphorated spiro[5.5]trienones in moderate to high yields.

Radical rearrangement of N-sulfonyl-N-aryl propynamides: proceeding with homolytic N–SO2 bond cleavage and 6-endo-dig cyclization toward 3-sulfonyl-2(1H)-quinolinones

A di-tert-butyl peroxide-promoted radical rearrangement of N-sulfonyl-N-aryl propynamides has been developed, giving 2-sulfonyl-3-aryl-2(1H)-quinolinones in moderate to good yields.

Switchable intramolecular oxidative amidation of 4-arylquinoline-3-carboxamides: divergent access to dibenzo[c,f][2,7]naphthyridinones and spirocyclohexadienones

A Na₂S₂O₈-mediated switchable oxidative cyclization of 4-arylquinoline-3-carboxamides is described.