S. L. Ioffe

Benzo-1,2,3,4-tetrazine 1,3-Dioxides: Synthesis and NMR Study

Benzo-1,2,3,4-tetrazine 1,3-dioxides (BTDOs) represent fairly stable high-nitrogen systems, incorporating two head-to-tail linked azoxy groups. The synthetic pathway to these heterocycles suggested the use of the tert-butyl-NNO-azoxy group as a building block, allowing the first azoxy group to be incorporated into the ring. The second azoxy group was added with the help of the oxodiazonium ion (−N=N=O+) or its synthetic equivalent. This could be generated by two new methods. The first of these involved treatment of N-nitroamines with nitrating agents, and the second treatment of diazonium salts with peracids in the presence of a base. The proposed key stage in the tetrazine 1,3-bis(N-oxide) ring formation is the reaction between the oxodiazonium ion and the distal nitrogen atom of the tert-butyl-NNO-azoxy group, followed by elimination of the tert-butyl cation. The syntheses of bromo-BTDOs 3b−f and nitro-BTDOs 4a−c are described. The BTDOs were characterized by NMR, including 14N and 15N experiments. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Synthesis and X‐Ray Crystal Structure of Bis‐3,3′‐(nitro‐ NNO‐azoxy)‐difurazanyl Ether

Explosive furazans The sequence of introducing the substituents to the target molecule 1, namely initial ether-bond construction and subsequent nitro-NNO-azoxy-group formation, favors the synthesis of this molecule.

Chemistry of N,N-Bis(silyloxy)enamines, Part 5†

Aliphatic nitro compounds can be considered as good precursors of a wide variety of α-azolyl-substituted oximes. The double silylation of convenient aliphatic nitro compounds and the subsequent N,C-coupling of the resulting N,N-bis(silyloxy)enamines 3 with N-silylated azoles 4 lead to the formation of the silylated α-azolyl-substituted oximes 6, which can be smoothly desilylated to give the target α-azolyl-substituted oximes 5. The mechanism of the key step of this process – N,C-coupling – includes the generation of corresponding conjugated nitrosoalkenes 7 (Schemes 4 and 5). The contribution of the chain mechanism in the overall process is considered as well. The studies of the scope and limitations of this reaction, as well as the optimization of its conditions were accomplished. The configuration of the CN bond in oximes was established by NMR.

Synthesis of PDE IVb Inhibitors. 3. Synthesis of (+)-, (−)-, and (±)-7-[3-(Cyclopentyloxy)-4-methoxyphenyl]hexahydro-3H-pyrrolizin-3-one via Reductive Domino Transformations of 3-β-Carbomethoxyethyl-Substituted Six-Membered Cyclic Nitronates

Simple three-step asymmetric and racemic syntheses of GlaxoSmithKlines highly potent PDE IVb inhibitor 1 were developed. The suggested approach is based on reductive domino transformations of 3-β-carbomethoxyethyl-substituted six-membered cyclic nitronates, which are easily accessed by a stereoselective [4 + 2] cycloaddition of an appropriate nitroalkene to vinyl ethers. In vitro studies of PDE IVb inhibition by enantiomeric pyrrolizidinones (+)-1 and (-)-1 were performed.

Synthesis of PDE IVb Inhibitors. 1. Asymmetric Synthesis and Stereochemical Assignment of (+)- and (−)-7-[3-(Cyclopentyloxy)-4-methoxyphenyl]hexahydro-3H-pyrrolizin-3-one

Asymmetric synthesis of GlaxoSmithKlines highly potent phosphodiesterase inhibitor 1 has been accomplished in nine steps and 16% overall yield. The original strategy suggested involves as a key step the silylation of enantiopure six-membered cyclic nitronates 4 obtained by a highly stereoselective [4 + 2]-cycloaddition of an appropriate nitroalkene 5 to trans-1-phenyl-2-(vinyloxy)cyclohexane. Functionalization of the resulting 5,6-dihydro-4H-1,2-oxazine and subsequent stereoselective reduction of 1,2-oxazine ring in intermediate 2 furnished the pyrrolizidinone framework with the recovery of chiral auxiliary alcohol.

Nucleophilic Aromatic Substitution of Hydrogen in the Reaction oftert-Alkylamines with Nitrosobenzenes – Synthesis and NMR Study ofN-(tert-Alkyl)-ortho-nitrosoanilines

The reaction of primary amines bearing tertiary alkyl groups (e.g. R–NH2; R = tBu, 1-adamantyl) with nitrosobenzenes has been found to proceed by oxidative nucleophilic aromatic substitution of hydrogen, thereby affording N-(tert-alkyl)-ortho- and -para-nitrosoanilines. The replacement of hydrogen proceeds more rapidly than the replacement of ortho- or para-nitro or -bromo substituents. With p-nitronitrosobenzene, both ortho-hydrogen atoms are substituted to afford N,N′-di(tert-alkyl)-4-nitro-2-nitroso-1,3-phenylenediamines 8a,b. The addition of oxidizing agents (e.g. MnO2) increases the yield of products. 1H-, 13C-, 14N- and 15N-NMR studies have confirmed the structures of the compounds under investigation. In ortho-nitrosoanilines, the rotamer with the nitroso group syn to the amino group is favored.

Synthesis and characterization of novel 1,2-oxazine-based small molecules that targets acetylcholinesterase.

Thirteen 2-oxazine-based small molecules were synthesized targeting 5-lipoxygenase (LOX), and acetylcholinesterase (AChE). The test revealed that the newly synthesized compounds had potent inhibition towards both 5-LOX and AChE in lower micro molar concentration. Among the tested compounds, the most active compound, 2-[(2-acetyl-6,6-dimethyl-4-phenyl-5,6-dihydro-2H-1,2-oxazin-3-yl)methyl]-1H-isoindole-1,3(2H)-dione (2a) showed inhibitory activity towards 5-LOX and AChE with an IC50 values of 1.88, and 2.5 μM, respectively. Further, the in silico molecular docking studies revealed that the compound 2a bound to the catalytic domain of AChE strongly with a highest CDOCKER score of -1.18 kcal/mol when compared to other compounds of the same series. Additionally, 2a showed a good lipophilicity (logP=2.66), suggesting a potential ability to penetrate the blood-brain-barrier. These initial pharmacological data revealed that the compound 2a could serve as a drug-seed in developing anti-Alzheimers agents.

β,β′-functionalized N,N-divinyl-N-trimethylsilyloxyamines via silylation of β-substituted aliphatic nitro compounds. The investigation of the mechanism of the process using selective trapping reagents

Abstract Hitherto unknown N,N-divinyl-N-trimethylsilyloxyamines of the general formula [XC(R)=ch]2NOSiMe3 (X = CO2Me. CN. 5-methyloxycarbonylisoxazolin-3-yl; R = H, Me, CH(Me)CO2Me) were obtained with moderate to good yields by silylation of nitro compounds XCH(R)CH2NO2 with N,O-bis(trimethylsilyl)acetamide. The mechanism of this reaction was studied by the example of silylation of methyl-3-nitropropionate using selective trapping reagents. Trimethylsilyl ester of the starting aci-nitro compound and methyl 2-nitroso acrylate were intercepted as consecutive intermediates. Thus, the silylation of β-functionalized nitro compounds could be presented as a convenient route to practically unknown β-substituted nitroso-alkenes XC(R)=CHNO which behave as active 1,3-heterodienes towards ethyl vinyl ether used as trapping reagent.

Radical Nitration-Debromination of α-Bromo-α-fluoroalkenes as a Stereoselective Route to Aromatic α-Fluoronitroalkenes—Functionalized Fluorinated Building Blocks for Organic Synthesis

A new highly efficient method for the synthesis of 2-fluoro-2-nitrostyrenes was described. Radical nitration of readily available 2-bromo-2-fluorostyrenes with Fe(NO3)3·9H2O resulted in the formation of the corresponding α-fluoro-nitroalkenes in isolated yields up to 92%. The reaction proceeded as a nitration-debromination sequence to highly stereoselectively give α-fluoro-nitroalkenes as Z-isomers only. The broad scope of this method was demonstrated. Prepared monofluorinated alkenes were shown to be versatile building blocks for the synthesis of various fluorinated products.

Synthesis of 4H-[1,2,3]triazolo[4,5-c][1,2,5]oxadiazole 5-oxide and its N- and O-alkyl derivatives

Abstract The synthetic route to the fused 1,2,3-triazole 2-oxide systems via intramolecular cyclization of N-nitroso and azido groups is described. The title compounds are characterized by 1H, 13C, 14N, 15N and 17O NMR spectroscopy.