Solid-phase tandem radical addition-cyclization reaction: triethylborane-induced reaction of oxime ethers anchored to polymer support

Tandem radical addition-cyclization of oxime ethers anchored to polymer support was studied. The reaction of oxime ethers with stannyl radical proceeded effectively by the use of triethylborane as a radical initiator. The alkyl radical addition-cyclization reactions of oxime ether connected with alpha,beta-unsaturated carbonyl group proceeded under iodine atom-transfer reaction conditions to give the functionalized azacycles via two carbon-carbon bonds-forming process.     

Tandem carbon-carbon bond-forming radical addition-cyclization reaction of oxime ether and hydrazone

The novel tandem radical addition-cyclization of oxime ethers and hydrazones intramolecularly connected with the alpha,beta-unsaturated carbonyl group is described. The radical reaction of oxime ethers 1, 2, and 4 connected with acryloyl and methacryloyl moieties proceeded smoothly to give the heterocycles via a tandem C-C bond-forming process. The tandem reaction of hydrazone 5 took place in the presence of Zn(OTf)(2) as a Lewis acid to give the trans-cyclic product 17 without the formation of the cis-isomer. The diastereoselective radical addition-cyclization reaction of chiral oxime ether 19 was also studied. The tandem reaction of 19 proceeded smoothly even in aqueous media, providing the novel method for asymmetric synthesis of gamma-butyrolactones and beta-amino acid derivatives.     

Carbon-carbon bond construction on solid support: triethylborane-induced radical reactions of oxime ethers

The triethylborane-induced solid-phase radical reaction was studied. The solid-phase radical reaction of oxime ether anchored to Wang resin proceeded smoothly to give the α-amino acid derivatives. The carbon-carbon bond-forming radical reaction of TentaGel OH resin-bound glyoxylic oxime ether proceeded even in aqueous media.     

Copper-catalyzed synthesis of oxime ethers from iminoxy radical (CN–O) and maleimides via radical addition

An efficient Cu(II)-catalyzed radical addition of maleimides has been achieved. The identified copper catalyst enables the formation of oxime radicals (N–O) by cleaving the O–H bond in ketoximes, followed by the radical addition to N-substituted maleimides. The oxime radicals (N–O) were detected and confirmed by EPR spectroscopy and variable-temperature ¹H NMR. The simple one-pot reaction realizes the facile preparation of a variety of oxime ether adduct products in moderate to good yields.     

Novel synthesis of substituted pyrrolidines and piperidines via radical addition-ionic cyclization reaction of oxime ethers

We have developed a novel synthetic route to nitrogen-containing heterocycles via radical addition-ionic cyclization reaction. Treatment of oxime ethers carrying the tosyloxy group with Et₃B and alkyl iodide in the presence of Lewis acid gave the substituted pyrrolidines and piperidines. The reaction of oxime ethers carrying the methoxycarbonyl group proceeded under the same conditions to give the amino esters, which were easily converted into the corresponding lactams by the treatment with concd HCl. On the other hand, the oxime ether bearing the phenoxycarbonyl group afforded directly alkylated lactams under the radical reaction conditions. The utility of this domino reaction was demonstrated by the synthesis of (±)-bgugaine and the formal synthesis of 5,8-disubstituted indolizidine alkaloids.     

Structure elucidation of the intermediate in triethylborane-mediated radical addition of oxime ethers with 2D- and 3D-DOSY NMR

The structures of the components in the triethylborane-mediated radical addition reaction of oxime ether were investigated by 1H- and 3D-DOSY NMR methods. It has been impossible to physically separate the unstable intermediates; therefore, the structures were thus far unidentified. It has been possible to elucidate the structures of these unstable intermediates using Diffusion-Ordered Spectroscopy (DOSY) methods for the reaction in an NMR tube. The DOSY methods resolved the spectra of each starting compound, intermediate and product having different diffusion coefficients. The structure of the intermediate was shown to be due to the bonding of diethylborane to the nitrogen atom of the alkoxyamino group.     

Chemoselective addition of organometallics to oxime ethers

In this paper, an efficient method for preparation of various substituted hydroxylamines from aldehydes is reported. We first prepare O-trimethylsilyl oxime ether in 5 M solution of lithiumperchlorate in diethyl ether (LPDE 5M) from condensation reaction between aldehyde and O-trimethylsilyl hydroxylamine, then add organosilane or organotin nucleophile in the same vessel to preparing the corresponding α-substituted hydroxylamines in one-pot synthesis.     

Ruthenium-catalysed conversion of oxime ethers into nitriles

The conversion of oxime ethers into nitriles has been achieved under neutral conditions using Ru(CO)(PPh₃)₃H₂ and the bidentate ligand Xantphos as the catalyst.     

The characteristics of oxime ethers upon electron-impact

The O-methyl ethers of aromatic and aliphatic aldoximes and ketoximes are characterized by hydrogen and skeletal rearrangements involving four-membered cyclic transition states. In the aliphatic compounds, four-centered rearrangement sometimes yields the species with the higher ionization potential, in contradiction of Audier's rule. The n-propyl oxime ethers show a novel skeletal rearrangement involving CH₂O elimination. The [M—H]+ process in the aromatic aldoxime ethers and an [M—Cl]+ process in an o-chloro derivative involve atom elimination by intramolecular aromatic substitution. Aromatic aldoxime ethers and the isomeric nitrones behave completely differently upon electron-impact.     

Iron-catalyzed cyanoalkylation of difluoroenol silyl ethers with cyclobutanone oxime esters

An iron-catalyzed coupling reaction of difluoroenol silyl ethers and cyclobutanone oxime esters is described. This protocol provides a convenient access to various previously unknown and potentially useful gem-difluoromethylenated ketonitriles inmoderate to good yields. The transformations of resulting products to other fluorinecontaining products is also documented.     

含哒嗪酮的肟醚类化合物的合成

4, 5-二氯哒嗪酮4与肟在NaH/DMF或者NaOH/acetone的条件下反应, 合成了含哒嗪酮的肟醚类化合物1a-f。4-氯-5(β-溴乙氧基)哒嗪酮3在相转移催化的条件下, 与芳香醛(酮)肟反应得到单一的产物2, 但是和脂肪酮肟反应则生成1和2的混合物。文中讨论了不同亲核试剂及反应条件下对该反应及其区域选择性的影响。     

Reduction of O-methyl oxime ethers of conjugated cyclohexenones with aluminum hydride

The reduction of representative O-methyl oxime ethers 1–4 with aluminum hydride in tetrahydrofuran yielded allylic amines and saturated aziridines as the main products. The stereochemical course of the reduction to aziridines depends on the oxime ether configuration. Thus, E–3, E–4 and Z–3, Z–4 gave 15, 16 and 21, 22 , respectively, with high stereoselectivity. Higher reactivity of Z than E isomers was utilized for the preparation of pure E isomers of oxime ethers from E, Z mixtures.     

Free-radical additions of ethers to fluorinated olefins

γ-Ray and peroxide-initiated additions of dimethylether to F-cyclobutene, F-cyclopentene, and F-cyclohexene give mixtures of $\text{cis}$- and $\text{trans}$-adducts and the stereochemistry of these processes will be discussed. A comparison of the reactivity of hexafluoropropene

towards radical additions of various cyclic ethers will be made which supports a rationale of the stabilising effect of oxygen on an adjacent radical centre.Bromination and chlorination of the adducts provides, at first sight, surprising variations in selectivity.     

Antiulcer agents. 2. Pyridyl oxime ethers

A large number of pyridinecarboxaldehyde (and ketone) O-substituted oximes were prepared by alkylating the oxime or by treating the parent aldehyde (or ketone) with an O-substituted hydroxylamine. Many of these were converted to the N-oxide. Screening revealed that many of these oxime ethers were active in preventing gastric ulcers in rats. Data on selected examples is given.