Aryl Ketenes Research Articles

Lewis Acid-Activated Reactions of Silyl Ketenes for the Preparation of α-Silyl Carbonyl Compounds.

Silyl-substituted ketenes are attractive molecular building blocks due to their stability and ease of storage, as opposed to unstable alkyl and aryl ketenes. To better understand the reactivity of silyl ketenes and, in turn, their use in the preparation of highly functionalized small molecules, the reaction of silyl ketenes with different nucleophiles was studied. The addition of alcohol, amine, or thiol nucleophiles to the central carbon of silyl ketene, followed by proton transfer afforded α-silyl ester, amide, or thio-ester, respectively. Catalytic amounts of Lewis acid greatly increase the rate of the reaction, and the impact of nucleophile, Lewis acid, and silyl substituent are evaluated. The small molecules produced from these reactions give insight into the use of silyl ketenes as building blocks for complex molecular structures.

ChemInform Abstract: Lewis Acid‐Promoted [2 + 2] Cycloadditions of Alkenes with Aryl Ketenes.

A method for the [2 + 2] cycloaddition of aryl ketenes and alkenes is presented. The process involves the in situ generation of a ketene in the presence of a Lewis acid. The utility of products is demonstrated towards the synthesis of a common scaffold found in several natural product families.

Lewis acid-promoted [2 + 2] cycloadditions of alkenes with aryl ketenes.

A method for the [2 + 2] cycloaddition of aryl ketenes and alkenes is presented. The process involves the in situ generation of a ketene in the presence of a Lewis acid. The utility of products is demonstrated towards the synthesis of a common scaffold found in several natural product families.

The Ketene‐Surrogate Coupling: Catalytic Conversion of Aryl Iodides into Aryl Ketenes through Ynol Ethers

Abstracttert‐Butoxyacetylene is shown to undergo Sonogashira coupling with aryl iodides to yield aryl‐substituted tert‐butyl ynol ethers. These intermediates participate in a [1,5]‐hydride shift, which results in the extrusion of isobutylene and the generation of aryl ketenes. The ketenes are trapped in situ with multiple nucleophiles or undergo electrocyclic ring closure to yield hydroxynaphthalenes and quinolines.

The ketene-surrogate coupling: catalytic conversion of aryl iodides into aryl ketenes through ynol ethers.

tert-Butoxyacetylene is shown to undergo Sonogashira coupling with aryl iodides to yield aryl-substituted tert-butyl ynol ethers. These intermediates participate in a [1,5]-hydride shift, which results in the extrusion of isobutylene and the generation of aryl ketenes. The ketenes are trapped in situ with multiple nucleophiles or undergo electrocyclic ring closure to yield hydroxynaphthalenes and quinolines.

Reaction of 1-arylmethylidenepyrazolidin-1-azomethine imines with aryl ketenes

A reaction of aryl ketenes with 1-arylmethylidenepyrazolidin-1-azomethine imines, generated by the diaziridine ring opening in 6-aryl-1,5-diazabicyclo[3.1.0]hexanes catalyzed with Et2O·BF3, leads to 1,2-bis(phenylacetyl)pyrazolidine, 2-arylacetyl-1-arylidenepyrazolidin-1-ium chlorides, or a representative of 1,5-diazabicyclo[3.3.0]octan-2-ones, viz., 4-(4-eth-oxyphenyl)-3,3-diphenyl-1,5-diazabicyclo[3.3.0]octan-2-one, depending on the reaction conditions and the structure of the starting compounds. A mechanism suggested earlier for the transformation of 1,5-diazabicyclo[3.1.0]hexanes in the reaction with ketenes was confirmed.

Asymmetric Synthesis of 3-Alkyl-3-aryl-oxindoles

Reported here is the asymmetric synthesis of 3-alkyl-3-aryloxindoles via a hetero-Claisen rearrangement. After developing a racemic synthesis of the process (eq. 1), the authors ­investigated the asymmetric version by treating Garner’s aldehyde 1 with phenylhydroxylamine to obtain (R,Z)-N-phenylnitrone 2 in 87% yield (eq. 2) as a single stereoisomer (confirmed by X-ray analysis). Treatment of nitrone 2 with methylphenyl­ketene at room temperature afforded the corresponding oxindole in 85% yield and 87% ee. The reaction was extended to a series of alkyl aryl ketenes; Garner’s aldehyde 1 was recovered in 78-87% yield. The proposed mechanism is under study in order to understand the enantioselectivity of this transformation.

4+2] Cycloaddition reaction: Synthesis of 7,9-diaryl-1,3,5-trimethyl- 2,4,8-trioxohexahydro-9H -pyrimido[2,1-g ]purine derivatives

[4+2] Cycloaddition reaction between 8-arylidincaminocaffiene and aryl ketene or chloro keten generated in situ from aryl acetyl chloride or chloro acetyl chloride and triethylamine) formed 7,9-diaryl-1,3,5-trimcthyl-2,4,8-trioxohexahydro-9H-pyrimido[2,1-g]purine in dioxane solvent is described.

( S)-(3-Hydroxy-4,4-dimethyl-2-oxopyrrolidin-1-yl) acetic acid as a solid supported chiral auxiliary in the asymmetric synthesis of β 2-homoarylglycines

Diastereoselective additions of the resin-supported ( S)-(3-hydroxy-4,4-dimethyl-2-oxopyrrolidin-1-yl) acetic acid to phthalimidomethyl aryl ketenes allow solid phase preparation of β 2-homoarylglycines with reasonable degrees of stereoselectivity.

Trimethylsilylated 1,3-dienes or styrenes from the reaction between trimethylsilyldiazomethane and vinyl or aryl ketenes

The reaction between trimethylsilyldiazomethane and aryl or vinyl ketenes 2 and 7, bearing an electron withdrawing group on the ketene moiety, gave rise in moderate to good yields to the trimethylsilylated styrenes 3–5 or 1,3 dienes 8a-d resulting from the decarbonylation of presumed intermediate cyclopropanones.

Cycloaddition Reaction: Synthesis of 5-Substituted 1,3,4-Thiadiazolo[3,2-a]pyrimidin-6-one

1,3,4-Thiadiazolo[3,2- a]pyrimidin-6-ones are synthesised by a (4 + 2) cycloaddition reaction of arylidineamino-1,3,4-thiadiazole and aryl ketenes formed in situ.

Cycloaddition Reaction: Synthesis of 5-Substituted 1,3,4-Thiadiazolo[3,2-a]pyrimidin-6-one

1,3,4-Thiadiazolo[3,2-a]pyrimidin-6-ones are synthesised by a (4+2) cycloaddition reaction of arylidineamino-1,3,4-thiadiazole and aryl ketenes formed in situ.

A comparative study of the decomposition of o-alkynyl-substituted aryl diazo ketones. Synthesis of polysubstituted .beta.-naphthols via arylketene intermediates

The photochemical, thermal, and rhodium-catalyzed decomposition reactions of several closely related o-alkynyl or o-alkenyl α-diazoaceto- and propiophenone derivatives have been studied. The reaction outcome is markedly dependent upon the reaction conditions employed for nitrogen extrusion. Thermolysis or photolysis of o-alkynyl α-diazopropiophenone derivatives yields polysubstituted β-naphthols. These products are derived from Wolff rearrangement of the initially formed carbene to give an aryl ketene which undergoes intramolecular cyclization onto the o-alkynyl substituent. In direct contrast to the thermal and photochemical results, Rh(II)-catalyzed decomposition yields products derived from direct attack of a rhodium carbenoid onto the tethered π-system producing a vinyl carbenoid intermediate

Acid-catalysed cyclisation of o-sulphonamido ketene dithioacetal S-oxides: a novel synthesis of the indole ring system

Treatment of o-sulphonamido aryl ketene dithioacetal S-oxides with hydrochloric acid in the presence of hydrogen sulphide gives 2-methylthioindoles.

Acid catalysed reactions of aryl ketene dithioacetal S-oxides: synthesis of chloroketene thioacetals and thioesters

Aryl ketene dithioacetal S-oxides, on treatment with hydrochloric acid in dichloromethane, give chloroketene thioacetals. The same reaction in the presence of hydrogen sulphide gives S-methyl thioesters.

Reactions of coordinated cyclic polyolefins. The kinetics and stereochemistry of the pericyclic [2,2]-sigmahaptotropic rearrangement

The [2,2]-sigmahaptotropic rearrangement of the [2 + 2] adducts of (cycloheptatriene)Fe(CO) 3 with aryl ketenes to the corresponding σ,π-allylic [3 + 2] adducts, in which a σ-bonded carbon and a Fe(CO) 3 fragment exchange bonding sites antarafacially across a σ carboncarbon bond, has been shown to proceed in a single kinetic step. The first order rate constants for the rearrangement are k 6.3 × 10 −6 s −1 (methanol, 23°C) and k 3.4 × 10 −6 s −1 (acetone, 51°C), with activation parameters Δ H # 21 kcal mol −1 and Δ S # − 12 e.u. (methanol). Rearrangement without ring opening occurred also in trifluoroethanol. The ratio between the rate constants in methanol and acetone at 51°C is moderate, k rel 40, indicating a partial charge separation in the transition state without formation of a fully developed zwitterionic intermediate. When the migrating carbon is unsymmetrically substituted, rearrangement occurs stereospecifically with retention of configuration. On the basis of these results a mechanism for the [2,2]-sigmahaptotropic rearrangement which involves a 2 a + (2 s + 2 a) mo (mo = metal-organic) thermally allowed pericyclic reaction is proposed.