Synthesis of pyrrolo-[2,1-j]quinolone framework via intramolecular electrophilic ipso-cyclization

Sc(OTf)3-Catalyzed Iodocyclization/Ritter-Type Amidation of N-Alkoxypropiolamides: A Synthetic Strategy for Isoxazol-3(2H)-ones

A Sc(OTf)₃-catalyzed iodocyclization/Ritter-type amidation of N-alkoxypropiolamides for the synthesis of 4-iodoisoxazol-3(2H)-ones bearing an amide group has been developed. This domino protocol allows the construction of a valuable heterocycle, isoxazol-3(2H)-one, as well as the introduction of two functional groups. The reaction has a broad substrate scope and can be carried out on a large scale. Control experiments suggest that Sc(OTf)₃ acts as a dual activator for both the iodocyclization and amidation steps. In addition, the N-alkoxy group in the substrate suppresses some of the side reactions.

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.

Selenium-promoted electrophilic cyclization of arylpropiolamides: synthesis of 3-organoselenyl spiro[4,5]trienones

This paper describes a selenium-promoted electrophilic cyclization of arylpropiolamides allowing the synthesis of 3-organoselenyl spiro[4,5]trienones via a 5-endo-dig ipso-mode. The 3-organoselenyl-quinolinone derivative formation via 6-endo-dig was avoided using an electrophilic organoselenium species in a metal-free protocol. The use of phenylselenyl bromide (1.3 equiv.), as the electrophilic source, in nitromethane (3 mL) at 90 °C enabled the cyclization of N-(2-methoxyphenyl)-N-methyl-3-phenylpropiolamides, giving 3-organoselenyl[4,5]triene-2,6-dione derivatives. The extension of the standard conditions to the N-(4-methoxyphenyl)-phenylpropiolamides led to the corresponding 3-organoselenyl spiro[4,5]trienones having the carbonyl group at the 8-position. Besides, we demonstrated a general application of our approach by using 3-organoselenyl spiro[4,5]trienones as substrates in Suzuki cross-coupling reactions, which gave the cross-coupled products in good yields.

A dearomative ipso-iodocyclization/desymmetrization sequence leading to optically active tricyclic piperazine scaffolds

Dearomative ipso-iodocyclization of 4-(1-ethoxyethoxy)-N-propargylanilines leading to 1-azaspiro[4.5]deca-3,6,9-trien-8-ones has been developed. This reaction is characterized by the yield of fewer toxic byproducts and is conducted by a more user-friendly protocol compared to other reported methods. The synthetic application of these spiro products was demonstrated by transformation of the iodo component into other functionalities. The desymmetrization of the resulting cyclohexadienones was also achieved by the diastereoselective aza-Michael addition of internal amino acid moieties to yield tricyclic piperazine scaffolds with two newly formed contiguous chiral centers.

Electrochemical Synthesis of Spiro[4.5]trienones through Radical-Initiated Dearomative Spirocyclization

A novel and green route has been developed for the electrochemical synthesis of spiro[4.5]trienones through radical-initiated dearomative spirocyclization of alkynes with diselenides. This metal-free and oxidant-free electrosynthesis reaction was performed in an undivided cell under mild conditions. A variety of selenation spiro[4.5]trienones products were prepared in moderate-to-good yields, showing a broad scope and functional group tolerance. Moreover, the developed continuous-flow system combined with electrosynthesis possesses the potential to achieve scaled-up reactions, overcoming the low efficiency of conventional electrochemical scaled-up reactions.

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%).

ipso-Cyclization: an emerging tool for multifunctional spirocyclohexadienones

Various ipso-annulation strategies to access diversely substituted spirocyclohexadienones and their applications have been presented.

ZnBr2-Mediated oxidative spiro-bromocyclization of propiolamide for the synthesis of 3-bromo-1-azaspiro[4.5]deca-3,6,9-triene-2,8-dione

ZnBr₂-Mediated oxidative ipso-bromocyclization of N-arylpropoilamide was utilized herein for the synthesis of 3-bromo-1-azaspiro[4.5]deca-3,6,9-triene-2,8-dione with high efficiency and a broad tolerance for functional groups.

Iodine-mediated synthesis of heterocycles via electrophilic cyclization of alkynes

Syntheses of heterocyclesvia5-exoor 6-endo-digiodocyclizations from alkynes.

Efficient Construction of Azaspiro[4.5]trienone Libraries via Tandem Ugi 4CC/Electrophilic ipso-Iodocyclization in One-Pot

A solution-phase parallel synthesis of pharmaceutically important azaspiro[4.5]trienones has been developed by performing tandem Ugi four-component condensation (U4CC), involving substituted p-anisidines, aldehydes, 3-alkyl/aryl-propiolic acids, and isocyanides, and iodine-mediated ipso-iodocyclization in one-pot. This highly atom economical process produced functionalized azaspiro[4.5]trienones in good to excellent overall yields and products were easily isolated by precipitation followed by crystallization. These vinyl-iodide bearing azaspiro[4.5]trienones were utilized for further modifications through Suzuki coupling and deiodination reaction to demonstrate the suitability of these products for various palladium catalyzed modifications. The present method provides an easy access to highly functionalized azaspiro[4.5]trienones that can be useful in drug discovery research.