Electrophilic Intermediates in the Nef and Meyer Reactions: A Computational Study.

The generation, interconversion, and reactivity of electrophilic species generated upon activation of nitroalkanes with protic acids (the Nef and Meyer reactions) were investigated by quantum-chemical calculations. ,-Bis(hydroxy)iminium (RC═N(OH)) and -oxoiminium (RC═N═O) cations were shown to be produced independently from -nitroalkanes, while -hydroxynitrilium cations (RC≡N-OH) were formed via nearly barrierless C-H bond cleavage in -oxoiminium cations. The -oxoiminium and -hydroxynitrilium cations whose formation is favored under highly acidic anhydrous conditions are strong electrophiles capable of reacting even with nonactivated arenes under ambient conditions.

An Intramolecular Nitroso-Meerwein-Ponndorf-Verley-Oppenauer Reaction to Access Fused Pyrrolidine Scaffolds.

δ-Hydroxy chloronitroso compounds generated from 1,2-oxazine -oxides undergo a 1,5-hydride transfer related to the Meerwein-Ponndorf-Verley-Oppenauer reaction. Based on the process discovered, a three-step access to fused pyrrolidine scaffolds containing up to four contiguous stereogenic centers starting from simple nitrostyrenes and cycloalkenes or cyclodienes has been developed. The suggested reaction mechanism was confirmed by UV-vis and ATR FT-IR monitoring and DFT calculations.

Interrupted Nef Reaction of Cyclic Nitronates: Diastereoselective Access to Densely Substituted α-Chloronitroso Compounds.

The reaction of cyclic nitronic esters (isoxazoline- and 5,6-dihydro-4-1,2-oxazine--oxides) with hydrochloric acid affords geminal chloronitroso compounds bearing a distant hydroxyl group. The reaction is usually diastereoselective, and in some cases stereodivergent formation of isomers at different temperatures is observed. The discovered process represents the first example of an interrupted Nef reaction of nitronic esters.

Construction of Saturated Oxazolo[3,2-][1,2]oxazines via Tandem [3+2]-Cycloaddition/[1,3]-Rearrangement of Cyclic Nitronates and Ketenes.

Reaction of six-membered cyclic nitronates with disubstituted ketenes affords hitherto unknown saturated oxazolo[3,2-][1,2]oxazines possessing up to four contiguous stereogenic centers. The process involves a tandem of [3+2]-cycloaddition across the C═O bond of ketene, followed by a spontaneous [1,3]-rearrangement of transient vinylidene-substituted bicyclic nitrosoacetals. DFT calculations of the mechanism suggest that the [1,3]-O,C-shift proceeds through a recyclization of a biradical intermediate formed by an unusually mild homolytic cleavage of the N-O bond.

Revealing the Structure of Transition Metal Complexes of Formaldoxime.

Aerobic reactions of iron(III), nickel(II), and manganese(II) chlorides with formaldoxime cyclotrimer (tfoH) and 1,4,7-triazacyclononane (tacn) produce indefinitely stable complexes of general formula [M(tacn)(tfo)]Cl. Although the formation of formaldoxime complexes has been known since the end of 19th century and applied in spectrophotometric determination of d-metals (formaldoxime method), the structure of these coordination compounds remained elusive until now. According to the X-ray analysis, [M(tacn)(tfo)] cation has a distorted adamantane-like structure with the metal ion being coordinated by three oxygen atoms of deprotonated tfoH ligand.

Nucleophilic Halogenation of Cyclic Nitronates: A General Access to 3-Halo-1,2-Oxazines.

In this article, comprehensive studies on the nucleophilic chlorination and bromination of readily available six-membered cyclic nitronates (1,2-oxazine--oxides) are reported. Under optimized conditions (POCl or (COBr) with Hünig's base), 3-halo-substituted 1,2-oxazines, which are difficult to access by other routes, were obtained in good to high yields. The latter were shown to be convenient precursors to other 3-substituted 1,2-oxazine derivatives using Lewis/Brønsted acid-assisted substitution of the halide atom for C-, S-, and N-nucleophiles.