Nitroalkanes as central reagents in the synthesis of spiroketals

(1E,3E)-1,4-Dinitro-1,3-butadiene-Synthesis, Spectral Characteristics and Computational Study Based on MEDT, ADME and PASS Simulation

The chemistry of conjugated nitrodienes is becoming increasingly popular. These molecules are successfully applied in cycloaddition to synthesize six-membered rings in Diels-Alder reactions. Nitrodienes can be also applied to obtain bis-compounds in [3+2] cycloaddition. Moreover, the presence of a nitro group in the structure provides a possibility of further modification of the products. The simplest symmetrical representative of conjugated nitrodienes is (1E,3E)-1,4-dinitro-1,3-butadiene. Although the first mentions of the compound date back to the early 1950s, the compound has not yet been examined thoroughly enough. Therefore, in this article, a comprehensive study of (1E,3E)-1,4-dinitro-1,3-butadiene has been described. For this purpose, an experimental study including the synthesis process as well as an evaluation of the spectral characteristics has been conducted. So as to better understand the properties of this compound, a computational study of reactivity indices based on MEDT and also an assessment of pharmacokinetics and biological activity according to ADME and PASS methodologies have been made. On this basis, some future application trends of (1E,3E)-1,4-dinitro-1,3-butadiene have been proposed.

Interrupted Nef and Meyer Reactions: A Growing Point for Diversity-Oriented Synthesis Based on Nitro Compounds

The Nef reaction (nitro to carbonyl group conversion) and related Meyer reaction are among the key transformations of aliphatic nitro compounds. The interrupted versions of these reactions in which the normal pathway is redirected to a different end product by an external nucleophile are much less common, albeit these processes substantially increase the synthetic potential of nitro compounds. In this review, examples of interrupted Nef and Meyer reactions are summarized, and the prospects of this methodology in diversity-oriented organic synthesis are analyzed. The bibliography contains 90 references.

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

Due to their intrinsic physical properties, which includes being able to perform as volatile liquids at room and biological temperatures, fragrance ingredients/intermediates make ideal candidates for continuous-flow manufacturing. This review highlights the potential crossover between a multibillion dollar industry and the flourishing sub-field of flow chemistry evolving within the discipline of organic synthesis. This is illustrated through selected examples of industrially important transformations specific to the fragrances and flavours industry and by highlighting the advantages of conducting these transformations by using a flow approach. This review is designed to be a compendium of techniques and apparatus already published in the chemical and engineering literature which would constitute a known solution or inspiration for commonly encountered procedures in the manufacture of fragrance and flavour chemicals.

Does electrophilic activation of nitroalkanes in polyphosphoric acid involve formation of nitrile oxides?

The mechanistic rationale involving activation of nitroalkanes towards interaction with nucleophilic reagents in the presence of polyphosphoric acid (PPA) was re-evaluated. Could nitrile oxide moieties be formed during this process? This experiment demonstrates that at least in some cases this could happen, as generated nitrile oxides were successfully intercepted as adducts of [3 + 2] cycloadditions.

The mechanistic rationale involving activation of nitroalkanes towards interaction with nucleophilic reagents in the presence of polyphosphoric acid (PPA) was re-evaluated. Could nitrile oxide moieties be formed during this process?

Organocatalytic Asymmetric Addition of Aldehyde to Nitroolefin by H-d-Pro-Pro-Glu-NH2: A Mechanistic Study

The mechanism of the asymmetric addition of aldehyde (butanal) to nitroolefin (β-nitrostyrene) catalyzed by H-d-Pro-Pro-Glu-NH₂ (dPPE-NH₂; 1) was explored using density functional theory methods in chloroform. By conformational search, it was confirmed that catalyst 1 and its enamine intermediate adopted a dominant conformation with a βI structure stabilized by a C₁₀ H-bond between the C=O of d-Pro1 and C-terminal NH₂ proton and by an additional H-bond between the side chain and the backbone of Glu3. This βI turn structure was conserved all along the catalytic cycle. Consistently with the kinetic studies, the C-C bond formation between the enamine and electrophile was also confirmed as the rate-determining step. The stereoselectivity results from a re → re prochiral approach of enamine and β-nitrostyrene with a gauche^- orientation of the double bonds. Although it was suggested as the possible formation of dihydrooxazine oxide species, this process was confirmed to be kinetically less accessible than the formation of acyclic nitronate. In particular, our calculated results supported that the carboxylic acid group of Glu3 in 1 played a central role by acting as general acid/base all along the catalytic cycle and orienting the asymmetric C-C bond formation.

Base-Catalyzed 1,6-Conjugate Addition of Nitroalkanes to p-Quinone Methides under Continuous Flow

A mild base-catalyzed protocol for the synthesis of substituted nitroalkane derivatives has been developed under continuous flow using a microreaction technique. This transformation basically involves the 1,6-conjugate addition of nitroalkanes to p-quinone methides, leading to the substituted nitroalkanes in good to excellent yields.

Iron-catalyzed unprecedented formation of benzo[d]imidazo[2,1-b]thiazoles under solvent-free conditions

The unprecedented formation of benzo[d]imidazo[2,1-b]thiazole during iron-catalyzed coupling of 2-aminobenzothiazole, aldehydes with nitroalkane in air has been observed.

An EPR study of the radical addition to 3-nitropentan-2-one as an archetype of α-carbonylnitroalkanes

Carbon, silicon, germanium, tin and lead-centered radicals were reacted with 3-nitropentan-2-one and 3-nitropentan-2-ol inside the cavity of an electron paramagnetic resonance spectrometer. In all cases, selective addition to the nitrogroup was observed with detection of the corresponding oxynitroxide radicals. In the case of the carbonyl substrate, alkyl acyl nitroxides were also detected because of α-photocleavage. The oxynitroxides decayed with a first order kinetics via fragmentation of the carbon-nitrogen bond (denitration). Unexpectedly, the activation parameters were fairly similar to those previously reported for the corresponding tert-butyl oxynitroxides and almost independent from the presence of a carbonyl or a hydroxyl group on the carbon adjacent to the one bearing the nitrogroup.

On the proposed structures and stereocontrolled synthesis of the cephalosporolides

The synthesis of four candidate stereoisomers of cephalosporolide H is described, made possible by a zinc-chelation strategy for controlling the stereochemistry of oxygenated 5,5-spiroketals. The same strategy likewise enables the first stereocontrolled synthesis of cephalosporolide E, which is typically isolated and prepared admixed with its spiroketal epimer, cephalosporolide F.