Angelo Mugnoli

Pyrrolidines, Pyrrolines and Pyrroles from 1,4-Diaryl-2,3-dinitro-1,3-butadienes via a 5-endo-trig Cyclization

The reactions between 1,4-diaryl-2,3-dinitro-1,3-butadienes 1a-d and primary alkylamines gave high yields of N-alkyl-2,5-diaryl-3-alkylamino-4-nitropyrrolidines 2 as pure all-trans diastereomers via an unusually favoured 5-endo-trig ring closure. The stereochemistry of compounds 2 has been attributed through an X-ray crystal structure analysis of the acetyl derivative 5 of 2ai. Amine elimination from 2 gave the N-alkyl-2,5-diaryl-3-nitro-3-pyrrolines 3 which could be easily aromatized to the corresponding pyrroles 4.

Access to 4,5‐Dinitro‐1,3,5,7‐octatetraene Systems

The reactions between 1,4-bis(diethylamino)-2,3-dinitro-1,3-butadiene (2), easily obtainable by ring-opening of 3,4-dinitrothiophene with diethylamine, and 2-substituted vinylmagnesium bromides gave good yields of the 4,5-dinitro-1,3,5,7-octatetraene derivatives 3a–e. With 1-phenylmagnesium bromide, conversely, only 3,4-dinitro-1,4-diphenyl-1,3,5-cyclooctatriene (4f) was obtained. From the unsubstituted dinitrooctatetraene 3a both the octatriene cycloisomer 4a and the valence tautomer of the latter (6a) could be isolated and characterized. The results obtained evidence an unfavourable effect of the two nitro groups on the cycloisomerization process of the octatetraene system.

LIPASE CATALYZED ASYMMETRIZATION OF QUINOLYL SUBSTITUTED 1,3-PROPANEDIOLS

Abstract 2-(2-Quinolyl)- and 2-(4-quinolyl)-1,3-propanediols 3 and 4 were prepared and asymmetrized by enantioselective acetylation in organic solvent catalyzed by lipases. While monoacetate 5 was best obtained using Celite-supported pig pancreatic lipase (PPL) (97.3% e.e.) as the (R)-enantiomer, both enantiomers of 6 have been obtained using different enzymes: (R)-6 using lipase from Aspergillus niger (84.0% e.e.) and (S)-6 using lipase from Candida antarctica (97.5% e.e.). The absolute configuration of both monoacetates 5 and 6 has been determined by anomalous X-ray dispersion methodology on the corresponding p-bromobenzoates 11 and 12.

Crystal structure of a very hindered olefin: 1,1-diphenyl-2,2-di-t-butylethylene at –155 °C

An X-ray crystal structure determination at –155 °C of 1,1-diphenyl-2,2-di-t-butylethylene, C22H28[monoclinic, space group C2/c, a= 32.703(3), b= 6.085(1), c= 20.747(2)A, β= 122.40(1)°, Z= 8, final R0.049 for 3 777 independent reflections) shows the steric hindrance effect on bond distances, valence angles, and twist of the central double bond (24°). Mean single-bond distances are: C(sp2)–C(sp2) 1.504, C(sp2)–C(sp3) 1.574, and C(sp3)–C(sp3) 1.546 A. Valence angles tend to narrow the hindrance of the t-butyl groups. The shortest 1.5-intramolecular contacts are C(Ph)⋯ C(But) 2.80 and C(But)⋯ C(But) 3.13 A. Intermolecular contacts are as expected. The conformation of the isolated molecule should differ little from that found in the crystal.

1,3-Cycloaddition of Benzonitrile Oxides to Diazepines. I. 1-Ethoxycarbonyl-5-methyl-1,2-diazepine

Stable aryl nitrile oxides (1a-e) and 1ethoxycarbonyl-5-methyl-1,2-diazepine (2) undergo 1,3cycloaddition reactions to give isomeric 1,2,4oxadiazole (3), 4,5-dihydroisoxazole (4) and isoxazole (5) derivatives, the first one being in any case the most abundant product. Overall kinetics were measured at temperatures in the range 50-90°C, in 1,1,2,2tetrachloroethane and mixtures of the latter with DMF; rate coefficients for the parallel reactions were, thus, obtained. Substituent and solvent effects are discussed

A very long carbon–carbon bond in a cyclopropane derivative

An X-ray crystal structure determination of 11,11-dimethyltricyclo[4,4,1,01,6]undeca-2,4,7,9-tetraene shows a C(I)–C(6) bond distance of ca. 1·80 A; the molecular geometry corresponds to a non-aromatic compound with a bisnorcaradiene structure.

Substituent effects on the gas-phase basicities of4-x-acetophanes and 4-x-2,6-dimethylacetophenones: a comparison with solution basicities

Abstract The behaviour towards gas-phase protonation of a series of 2,6-dimethyl-4-X-acetophenones DM1 exhibits strong similarities with that of the corresponding 4-X-acetophenones 1 . A comparison with previous basicity data in solution and AM1 semiempirical calculations suggest that the X-dependent rotation of the probe group out of the plane of the aromatic ring caused by the two ortho methyls is of minor importance in influencing the substituent effect on the gas-phase basicity of DM1 ; on the contrary, it could heavily affect the solvatability and thus be responsible for the observed behaviour of DM1 in strongly acidic media.

A new ring transformation: conversion of 6-p-chlorophenyl-3-methyl-5-nitrosoimidazo[2,1-b]thiazole into 8-p-chlorophenyl-8-hydroxy-5-methyl-3-oxo-1,2,4-oxadiazolo[3,4-c][1,4-]thiazine by the action of mineral acids

6-p-Chlorophenyl-3-methyl-5-nitrosoimidazo[2;1-b]thiazole 1 by treatment with dilute hydrochloric acid in dioxane at room temperature gave 8-p-chlorophenyl-8-hydroxy-5-methyl-3-oxo-1,2,4-oxadiazolo[3,4-c][1,4]thiazine 2, containing a new condensed ring system the molecular structure of which was ascertained by physical methods (1H and 13C NMR, electron impact-mass and IR spectra, and XRD).

Secondary steric effects in SNAr of thiophenes: a coordinatekinetic, thermodynamic, UV–VIS, crystallographic and ab initiostudy

The reactivity of some dinitro-benzene and -thiophene derivatives with piperidine and sodium benzenethiolate has been examined giving evidence that benzenes show large and thiophenes show small kinetic secondary steric effects, respectively. The acid dissociation reaction and the UV–VIS spectra of some nitrothiophenamines have also been studied. The crystal structure and the absolute conformation of 2-iodo-3,5-dinitrothiophene and of 2-iodo-4-methyl-3,5-dinitrothiophene have been determined. For different conformations of the analogous chlorodinitro derivatives in the thiophene and benzene series, ab initio energy calculations have been performed. The results collected show that steric strain among adjacent groups affects the benzene and thiophene compounds and the kinetic, thermodynamic and spectroscopic properties of the molecules examined differently. Differences in geometry of the two aromatic rings and then in rotation of nitro groups with respect to the rings themselves as well as differences along reaction coordinates (essentially depending on hybridation changes) are used to explain the above data.

Synthesis and reactivity of (1S,4S,5S)-5-bromo-1,3,3-trimethyl-N-nitro-2-oxabicyclo[2.2.2]octan-6-imine. X-Ray molecular structure and absolute configuration of E and Z isomers of (1S,4S)-5,5-dibromo-1,3,3-trimethyl-N-nitro-2-oxabicyclo[2.2.2]octan-6-imine, the first case of separated nitrimine isomers

The potassium salt 2 of 1,3,3-trimethyl-N-nitro-2-oxabicyclo[2.2.2]octan-6-imine 1 reacted with bromine in acetic acid solution to give (1S,4S,5S)-5-bromo-1,3,3-trimethyl-N-nitro-2-oxa-bicyclo[2.2.2]octan-6-imine 3. Bromination of the salt 2 in methanolic potassium hydroxide afforded a mixture of (1S,4S)-5,5-dibromo-1,3,3-trimethyl-N-nitro-2-oxabicyclo[2.2.2]octan-6E-and -6Z-imine 4 and 5, whose X-ray crystal-structure determinations allowed their absolute configurations to be established. Bromination of monobromide 3 under different conditions gave the dibromide 4, which was converted into isomer 5 by storage in chloroform solution. Nitrimine 3 reacted with hydroxylamine hydrochloride and sodium hydroxide or piperidine to give (1S,4S,5S)-5-bromo- and -5-hydroxyamino-N-hydroxy-1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-6-imine or (1S,4S,5S)-N-hydroxy-1,3,3-trimethyl-5-(piperidin-1-yl)-2-oxabicyclo[2.2.2]octan-6-imine. Reaction of compound 3 with aliphatic and aromatic primary amines afforded N-substituted (1S,4S,5S)-5-bromo-1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-6-imines. Reduction of compound 3 with sodium cyanoborohydride gave (1S,4S,5S)-5-bromo-1,3,3-trimethyl-N-mtro-2-oxabicyclo[2.2.2]octan-6-amine, whereas consecutive treatment with potassium hydroxide and aq. hydrochloric acid afforded the less stable isomer (1S,4S)-5-bromo-1,3,3-trimethyl-N-nitro-2-oxabicyclo[2.2.2]oct-5-en-6-amine.