Reaction Of Oxime Ethers Research Articles

Heterocycle synthesis via radical reactions

Abstract A novel synthetic method for the preparation of nitrogen-containing heterocycles via the route involving domino-type radical addition/cyclization reaction of oxime ethers is described. Alkyl radical addition/cyclization of oxime ethers carrying an appropriate leaving group proceeded smoothly to form the alkylated nitrogen-containing heterocyclic compounds. Additionally, tin-mediated radical addition/cyclization/elimination (RACE) reaction of oxime ethers is newly found and successfully applied to an asymmetric total synthesis of (-)-martinellic acid.

Efficient Synthesis of Benzofurans Utilizing [3,3]‐Sigmatropic Rearrangement Triggered by N‐Trifluoroacetylation of Oxime Ethers: Short Synthesis of Natural 2‐Arylbenzofurans

AbstractA new synthetic method for the preparation of benzofurans has been developed. The key step of this method is the [3,3]‐sigmatropic rearrangement of N‐trifluoroacetyl‐ene‐hydroxylamines, which was triggered by acylation of oxime ethers. TFAA has been proved to be the best reagent to induce [3,3]‐sigmatropic rearrangement for the synthesis of cyclic oracyclic dihydrobenzofurans. On the other hand, the TFAT‐DMAP system is found to be the most effective for constructing various benzofurans. Synthetic utility of this reaction is demonstrated by the short synthesis of natural benzofurans without protection of the hydroxy group. The synthesis of Stemofuran A was accomplished via condensation of ketones with aryloxyamine and subsequent reaction with TFAT‐DMAP in a four‐step synthesis with 72 % overall yield. Similarly, Eupomatenoid 6 and Coumestan were synthesized through the reaction of oxime ether with TFAT‐DMAP. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

トリフルオロアセチル基の特性を利用した複素環化合物の効率的合成

We have developed a new and efficient synthetic method for functionalized indoles and benzofurans via the route involving [3, 3] -sigmatropic rearrangement of N-trifluoroacetyl enamine.N-Trifluoroacetyl enehydrazine carrying a cyclopentene ring smoothly underwent [3, 3] -sigmat-ropic rearrangement followed by cyclization to give indoline in excellent yield. Cyclohexenyl or acyclic N-trifluoroacetyl enehydrazines gave indoles in good yields. The rearrangement of N-trifluoroacetyl enehydrazines proceeded smoothly even under either aqueous or solvent-free conditions.The acylation of cyclic or acyclic oxime ethers with TFAA proceeded under mild conditions to give the dihydrobenzofurans in excellent yields without the isolation of N-trifluoroacetyl enehydoxylamine. On the other hand, the reaction of oxime ethers with trifluoroacetyl triflate (TFAT) in the presence of DMAP gave the benzofurans in good yields. It is noteworthy that dihydrobenzofurans or benzofurans can be formed selectively from the same substrate by changing only the reagent. This successive method was successfully applied to the synthesis of natural products.

Zinc‐Mediated Carbon Radical Addition to Glyoxylic Imines in Aqueous Media for the Synthesis of α‐Amino Acids.

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Zinc-mediated carbon radical addition to glyoxylic imines in aqueous media for the synthesis of α-amino acids

The addition of carbon radicals to glyoxylic imines was studied using zinc dust as a radical initiator. The zinc-mediated radical reaction of glyoxylic oxime ethers and hydrazones proceeded smoothly to give the alkylated products via a carbon-carbon bond-forming process in aqueous media. The reaction of the oxime ethers and hydrazones having an Oppolzer's camphorsultam group provided the corresponding alkylated products, which could be converted into enantiomerically pure alpha-amino acids. The diastereoselectivities observed in the reaction of hydrazones were better than those obtained in the reaction of oxime ethers.

Development of Carbon Radical Addition to Imine Derivatives

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Development of carbon radical addition to imine derivatives

This review summarizes the new carbon-carbon bond construction methods based on the radical reaction of imine derivatives. The intermolecular carbon radical addition to oxime ethers proceeded smoothly in the presence of BF3.OEt2. A high degree of stereocontrol in the reaction of oxime ethers was achieved to give amino acid derivatives with excellent diastereoselectivities. The radical reaction of imine derivatives in water has also been investigated. The radical cyclization of oxime ethers proceeded effectively to provide the functionalized heterocycles via a carbon-carbon bond-forming process. These reactions were extended to the solid-phase radical reactions using triethylborane or diethylzinc as a radical initiator.