Α-bromocarbonyl Compounds Research Articles

Organocatalytic Enantioselective Alkylation of Aldehydes with [Fe(bpy)3]Br2 Catalyst and Visible Light

Catalytic amounts (2.5 mol %) of [Fe(bpy)3]Br2 complex in the presence of visible light and the MacMillan catalyst 3 (20 mol %) are highly effective in promoting an enantioselective organocatalytic photoredox alkylation of aldehydes with various α-bromo carbonyl compounds. Reaction yields of isolated compounds and enantioselectivities are very good and comparable to the ones obtained by [Ru(bpy)3]2+, organic dyes, or semiconductors, in the presence of the same organocatalysts. The use of first-row, abundant, and cheap metals in photocatalyzed reactions can open new perspectives in stereoselective organic synthesis.

ChemInform Abstract: Palladium‐Catalyzed Cross‐Coupling of α‐Bromocarbonyls and Allylic Alcohols for the Synthesis of α‐Aryl Dicarbonyl Compounds.

The palladium-catalyzed coupling of olefins and organohalides is a versatile approach for synthesizing complex molecules from simple starting materials. We have developed a palladium-catalyzed coupling of α-bromocarbonyl compounds with allylic alcohols for the generation of acyclic aryl-substituted dicarbonyl compounds. The reaction proceeds via a tandem olefin insertion of an α-acyl radical followed by a 1,2-aryl migration. In addition to providing preliminary evidence for a free radical mediated mechanism, we demonstrate unprecedented levels of 1,3-stereoinduction for the 1,2-migration step.

ChemInform Abstract: Synthesis of 2‐Unsubstituted 1,3‐Selenazoles by Cyclization of Selenoformamide with α‐Bromocarbonyl Compounds.

2-Unsubstituted 1,3-selenazoles were prepared by cyclization of selenoformamide with α-bromoacetophenones. Parent 1,3-selenazole was prepared by cyclization of selenoformamide with α-bromoacetaldehyde.

Fe-Mediated S–S Bond Cleavage and Its Application in the Synthesis of α-Arylthio Carbonyl Compounds

In the presence of iron dust, diaryl disulfides react with α-bromo carbonyl compounds to obtain α-arylthio carbonyl compounds in good yield at 90 °C under an N2 atmosphere, using commercial dimethylformamide (DMF) as solvent. The possible reaction mechanism is that the disulfide is reduced by iron dust to give ArSFeSAr and then reacted with α-bromo carbonyl compounds to give product α-arylthio carbonyl compounds and FeBr2.

Iron-Mediated Cleavage of Se—Se Bond for the Synthesis ofα-Arylseleno Carbonyl Compounds

In the presence of iron dust, using commercial N,N-dimethylformamide (DMF) as solvent, diaryl diselenides re- acted with α-bromo carbonyl compounds at 90 ℃ under nitrogen atmosphere to afford a series of α-arylseleno carbonyl compounds. The influence of temperature, reaction time, solvent and iron dosage on the reaction was investigated. The results showed that the influence of temperature on the reaction was most obvious. In addition, the influence of carbonyl substituent in α-bromo carbonyl compounds was also more obvious. When carbonyl substituent is phenyl, the yield was lower than that of methyl or alkoxy. A proposal mechanism is that iron dust reacted with diaryl diselenides to give the nucleophilic species ArSeFeSeAr, and nucleophilic species ArSeFeSeAr and electrophilic α-bromo carbonyl compounds occured nucleophilic substitution reaction to obtain the desire products. The method using the iron dust to promote the cleavage of Se—Se bond has advantages of safe non-toxic, cheap and easy to get raw materials, simple procedure. Keywords iron dust; cleavage of Se—Se bond; diaryl diselenides; α-bromo carbonyl compounds; α-arylseleno carbonyl compounds

Regioselective synthesis of 2H-indazoles through Ga/Al- and Al-mediated direct alkylation reactions of indazoles.

A procedure has been developed for the regioselective, high yielding synthesis of 2H-indazoles that involves direct alkylation of indazoles with various allyl and benzyl bromides, and α-bromocarbonyl compounds.

Palladium-Catalyzed Cross-Coupling of α-Bromocarbonyls and Allylic Alcohols for the Synthesis of α-Aryl Dicarbonyl Compounds.

The palladium-catalyzed coupling of olefins and organohalides is a versatile approach for synthesizing complex molecules from simple starting materials. We have developed a palladium-catalyzed coupling of α-bromocarbonyl compounds with allylic alcohols for the generation of acyclic aryl-substituted dicarbonyl compounds. The reaction proceeds via a tandem olefin insertion of an α-acyl radical followed by a 1,2-aryl migration. In addition to providing preliminary evidence for a free radical mediated mechanism, we demonstrate unprecedented levels of 1,3-stereoinduction for the 1,2-migration step.

ChemInform Abstract: Three‐Component Coupling Reaction Triggered by Insertion of Arynes into the S=O Bond of DMSO.

An unprecedented three-component coupling reaction of arynes, α-bromo carbonyl compounds, and DMSO triggered by insertion of arynes into the S═O bond of DMSO has been developed. The reaction can generate a wide range of multisubstituted aryl methyl thioethers in good yields, wherein DMSO serves as both methylthiolation reagent and oxygen source.

One-pot synthesis of 12H-benzo[b]xanthen-12-ones and naphtha[2,3-b]furans from non-naphthalene substrates

An efficient one-pot synthesis of 12H-benzo[b]xanthen-12-ones via an oxidant initiated and base promoted tandem reaction of 2-(4-(2-haloaryl)-4-hydroxybut-1-ynyl)benzaldehydes has been developed. By using similar strategy, a one-pot synthesis of naphtha[2,3-b]furans from the cascade reaction of 2-(4-hydroxy-but-1-ynyl)benzaldehydes with 2-bromoacetonitrile or α-bromocarbonyl compounds has also been achieved.

Light-driven organocatalysis using inexpensive, nontoxic Bi2O3 as the photocatalyst.

The development of enantioselective catalytic processes that make use of sunlight as the energy source and nontoxic, affordable materials as catalysts represents one of the new and rapidly evolving areas in chemical research. The direct asymmetric α-alkylation of aldehydes with α-bromocarbonyl compounds can be successfully achieved by combining bismuth-based materials as low-band-gap photocatalysts with the second-generation MacMillan imidazolidinone as the chiral catalyst and simulated sunlight as a low-cost and clean energy source. This reaction also proceeded with high efficiency when the reaction vial was exposed to the morning sunlight on a clear September day in Tarragona, Spain.

Three-component coupling reaction triggered by insertion of arynes into the S═O bond of DMSO.

An unprecedented three-component coupling reaction of arynes, α-bromo carbonyl compounds, and DMSO triggered by insertion of arynes into the S═O bond of DMSO has been developed. The reaction can generate a wide range of multisubstituted aryl methyl thioethers in good yields, wherein DMSO serves as both methylthiolation reagent and oxygen source.

Iridium-catalyzed isomerization/bromination of allylic alcohols: synthesis of α-bromocarbonyl compounds.

α-Brominated ketones and aldehydes, with two adjacent electrophilic carbon atoms, are highly valuable synthetic intermediates in organic synthesis, however, their synthesis from unsymmetrical ketones is very challenging, and current methods suffer from low selectivity. We present a new, reliable, and efficient method for the synthesis of α-bromocarbonyl compounds in excellent yields and with excellent selectivities. Starting from allylic alcohols as the carbonyl precursors, the combination of a 1,3-hydrogen shift catalyzed by iridium(III) with an electrophilic bromination gives α-bromoketones and aldehydes in good to excellent yields. The selectivity of the process is determined by the structure of the starting allylic alcohol; thus, α-bromoketones formally derived from unsymmetrical ketones can be synthesized in a straightforward and selective manner.

ChemInform Abstract: A Simple, Three‐Component Synthesis of 2‐Aminothiazoles Using Trimethylsilyl Isothiocyanate.

AbstractMulticomponent reactions of α‐bromocarbonyl compounds, aromatic or aliphatic amines, and TmsNCS are developed to give fully substituted 2‐aminothiazoles.

ChemInform Abstract: Nickel‐Catalyzed Direct Alkylation of Heterocycles with α‐Bromo Carbonyl Compounds: C3‐Selective Functionalization of 2‐Pyridones.

Nickel HAS it: A Ni(cod)2/dppp catalyst system promotes the direct alkylation of electron-rich heterocycles with α-bromo carbonyl compounds and involves an alkyl radical intermediate (see scheme; cod = 1,5-cyclooctadiene, dppp = 1,3-bis(diphenylphosphino)propane). This homolytic radical aromatic substitution (HAS)-type reaction enables the C3-selective direct functionalization of 2-pyridones.

Solvent-Free Synthesis of Functionalized Thiazoles Using Multicomponent Reaction of Isothiocyanates

An efficient synthesis of thiazoles is described via an one-pot reaction between acid chlorides, ammonium thiocyanate tetramethylguanidine and α-bromocarbonyl compounds under solvent-free conditions without using any catalyst. The method offers several advantages including high yields of products and an easy work-up procedure at room temperature in excellent yield.

A simple, three-component synthesis of 2-aminothiazoles using trimethylsilyl isothiocyanate

Abstract The first multicomponent, solution-phase protocol to prepare privileged 2-aminothiazoles from α-bromocarbonyl compounds and amines (aromatic and aliphatic) using commercially available trimethylsilyl isothiocyanate is described.

Nickel‐Catalyzed Direct Alkylation of Heterocycles with α‐Bromo Carbonyl Compounds: C3‐Selective Functionalization of 2‐Pyridones

Nickel HAS it: A Ni(cod)2/dppp catalyst system promotes the direct alkylation of electron-rich heterocycles with α-bromo carbonyl compounds and involves an alkyl radical intermediate (see scheme; cod = 1,5-cyclooctadiene, dppp = 1,3-bis(diphenylphosphino)propane). This homolytic radical aromatic substitution (HAS)-type reaction enables the C3-selective direct functionalization of 2-pyridones.

Unexpected formation of pyrrolo[1,2-a]quinoxaline derivatives during the multicomponent synthesis of pyrrolo[1,2-a]benzimidazoles

New pyrrolo[1,2-a]benzimidazole and pyrrolo[1,2-a]quinoxaline derivatives are obtained via one-pot, three-component reactions from 1-benzylbenzimidazoles, α-bromocarbonyl compounds, and non-symmetrical activated acetylenic dipolarophiles in propylene oxide as both the reaction medium and acid scavenger, at room temperature. When the same reaction is performed in 1,2-epoxybutane at reflux temperature only the pyrrolo[1,2-a]benzimidazole derivative is obtained.

Acceleration of the Eschenmoser coupling reaction by sonication: efficient synthesis of enaminones

Enaminones are commonly prepared by the Eschenmoser coupling reaction. The duration of the reaction is often long. Here, we describe how sonication can accelerate this reaction. The reaction conditions provide an efficient method for the coupling of primary, secondary and tertiary thioamides with α-bromocarbonyl compounds.

Efficient preparation of highly substituted thiophenes and thiophene-based arylacetic acids

An efficient and one-step method for the preparation of highly substituted thiophenes and thiophen-2-yl-acetic acid derivatives was developed. Hence, thioacetomorpholides were smoothly reacted with α-bromo carbonyl compounds in [bmim]OH as an efficient dual catalyst-reaction medium to produce the title compounds in good yields.