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An accurate crystal structure determination has provided evidence for a planar conformation for 3-acetylamino-5-methyl-1,2,4-oxadiazole (5), in agreement with quantum-mechanical calculations in the gas phase. In the crystal, a series of strong intermolecular N7H7….O9 hydrogen bonds link the amido groups of different molecules, causing the formation of infinite parallel ordered chains. The effect of the DMSO solvent on the energy and charge distribution of compound 5 and on its relevant 5− anion, involved in a fully degenerate rearrangement (FDR), has been deepened by quantum-mechanical DFT calculations. The calculated energy barrier for the FDR increases in going from in vacuo to DMSO, in agreement with previsions based on the Hughes and Ingold rules concerning the nucleophilic substitution of an anionic reagent (the deprotonated amido group in the side chain) on a neutral substrate (the 1,2,4-oxadiazole ring). Copyright © 2009 John Wiley & Sons, Ltd.

The treatment of 3,4-dinitrothiophene with an aryl Grignard reagent results in the reduction of one nitro group accompanied by the ipso-substitution of a hydrogen atom by an ortho-phenolic group on the ring carbon adjacent to the reduced nitro group. A Claisen-type intramolecular rearrangement is proposed as the pivotal step of a rather complex mechanism, followed by proton-transfer aromatizing steps. This work shows yet another facet of the variegated reactivity of 3,4-dinitrothiophene towards nucleophiles. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Within an overall ring-opening/ring-forming protocol, the (E,E)-4-methylthio-2-nitro-3-phenylsulfonyl-1-pyrrolidino-1,3-butadiene (7) [derived from the initial opening of 3-nitro-4-(phenylsulfonyl)thiophene (6) with pyrrolidine and silver nitrate in EtOH] is revealed to be an excellent precursor of nitro(phenylsulfonyl) derivatives of ring-fused aromatic (naphthalene, phenanthrene) or heteroaromatic (benzothiophene) compounds whose substitution pattern cannot be easily achieved by conventional methods. The key step is represented by a thermal electrocyclic rearrangement of (E,E)-1-aryl-4-methylsulfonyl-2-nitro-3-phenylsulfonyl-1,3-butadienes (9), which, thanks to proper geometric and electronic factors, occurs in unprecedentedly mild conditions and is followed by an irreversible, concerted syn β-elimination of methanesulfinic acid to aromatize the newly formed cyclohexadienic ring.

An accurate crystal structure determination has provided evidence for a planar conformation for 3-acetylamino-5-methyl-1,2,4-oxadiazole (5), in agreement with quantum-mechanical calculations in the gas phase. In the crystal, a series of strong intermolecular N7H7...O9 hydrogen bonds link the amido groups of different molecules, causing the formation of infinite parallel ordered chains. The effect of the DMSO solvent on the energy and charge distribution of compound 5 and on its relevant 5S anion, involved in a fully degenerate rearrangement (FDR), has been deepened by quantum-mechanical DFT calculations. The calculated energy barrier for the FDR increases in going from in vacuo to DMSO, in agreement with previsions based on the Hughes and Ingold rules concerning the nucleophilic substitution of an anionic reagent (the deprotonated amido group in the side chain) on a neutral substrate (the 1,2,4-oxadiazole ring).

The reactions between 1,2-bis(diethylamino)-2,3-dinitro-1,3-butadiene, easily obtainable by ring-opening of 3,4-dinitrothiophene with diethylamine, and arylmethylmagnesium chlorides in THF at 0°C furnished good yields of (E,E,E)-1,6-diaryl-3-nitro-1,3,5-hexatrienes. To explain the formation of the hexatrienes, a mechanism is advanced which involves, in particular, tautomerisation of the intermediate 1,6-diaryl-3,4-dinitro-2,4-hexadienes followed by base-induced elimination of nitrous acid. The electrocyclic disrotatory conversion of the hexatrienes into the corresponding 5,6-diaryl-2-nitro-1,3-cyclohexadienes was analysed by 1H NMR spectroscopy and exploited for the high-yielding synthesis of 1,2-diaryl-4-nitrobenzenes employing, as oxidants, either DDQ or iodine in the presence of cyclohexene oxide as HI scavenger.

Two clerodane diterpenoids, blepharolides A and B, have been isolated from Salvia blepharophylla Brandegee ex Epling. Their structures were determined using a combination of one- and two-dimensional NMR techniques. The relative stereochemistry for blepharolide A was determined by X-ray diffraction. To our knowledge this is the first crystal structure determination of a 5,6-unsaturated octahydro-1H-cyclopropa[a]naphthalene derivative.

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.

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.

The reactions of 1,4-disubstituted 2,3-dinitro-1,3-butadienes 1a-g in THF with isocyanides XCH2NC (TosMIC, X = tosyl; TBICA, X = COOBut) and DBU furnish good to moderate yields of 2,3-disubstituted 4-ethynylpyrroles 5a-g or 6a-g. In the reaction of 1g with TosMIC and DBU the nitrovinyl pyrrole 7g and the 3,3′-dipyrrole 4g are also isolated as by-products. A mechanism involving sequential base-induced addition, elimination and cyclization steps is advanced to account for the formation of the isolated products.

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.

The structure of ethyl 5-methyl- 10-(2,4,6-trimethylphenyl)-8-oxa-1,2,9-triazabicyclo[5.3.0]deca-3,5,9-triene-2-carboxylate (I) has been determined. The 1,2-diazepine ring has a twisted-sofa form and the 1,2,4-oxadiazole ring has an envelope conformation, with the bridgehead C7 atom out of the plane of the ring. The terminal methyl group of the side chain is disordered, being split over two different positions

The reactivity of 6-(4-chlorophenyl)-3-methyl-5-nitrosoimidazo[2,1-b][1,3]thiazole (a member of a class of mutagenic compounds) with hydrochloric acid in ethanol has been investigated and the nature of the reaction product unambiguously established on the basis of infrared, NMR and mass spectra and a crystal structure determination.

In the crystal structure of the novel acyl­thio­carbamate derivative O-[2-(1,3-dioxo-2,3-dihydro-1H-isoindol-2-yl)­ethyl] N-(4-methyl­phenyl)-N-(3-nitro­benzoyl)thio­carbamate, C25H19N3O6S, intra- and inter­molecular π–π inter­actions occur between the phthalimide and N-benzoyl moieties. The partial atomic charges, calculated by ab initio methods, are consistent with the observed structure.

1-(Methyl-p-tolyl-amino)-3-phenoxy-2-azetidinones 4-COX and 4-R substituted (COX: X=Me, Et, Ph, NMe2, NEt2, OBut; R=Me, Et, Ph) were smoothly prepared from the corresponding α-(methyl-p-tolyl)hydrazonylated ketones, amides and esters via [2+2] cycloaddition with phenoxyketene. The reaction was generally high-yielding and diastereoselective, leading to β-lactams with a cis relationship between the PhO and the COX moieties, except for R=Ph, where an opposite stereoselectivity was instead observed. The azetidinones represent interesting intermediates which couple protection at N(1) and functionalization at position 4 of the ring. Deprotection of N(1) can be easily attained by oxidative N–N cleavage with magnesium monoperoxyphthalate.

The 'Tenuta di Castelporziano' (Castelporziano Presidential Estate) is an important area for the study of Mediterranean coastal and dune ecosystems. The need of providing a new and detailed Vegetation Map rose for the environmental monitoring of that area and its efficient management. All activities were developed using remote sensing images acquired by a new 12 band DAEDALUS sensor, in the course of a specific monitoring aero-campaign organized by ENEA. The realization of the map, lasted one year, can be divided into two blocks: (1)remote sensing image processing methodologies, developed at the ENEA-Casaccia Research Center (Rome), by experts of Remote Sensing Department; and (2) 'in situ' work, realized by ecologists and botanical experts of University of Rome 'La Sapienza'. Image processing steps were organized as follows: (i) geometric correction and georeferencing of the images; (ii) classification; (iii) mosaicking; (iv) conversion into vector layer and editing. As concerns image processing, ERDAS/IMAGINE system was used, while ARC/INFO system was used for vector layers management and map printing. At the end of all activities the map accuracy was tested by a statistical procedure: the global accuracy was about of 88%. The map is integrated in a information system (SITAC), a GIS realized by ENEA.

Within an overall ring-opening/ring-forming protocol, the (E,E)-4-methylthio-2-nitro-3-phenylsulfonyl-1-pyrrolidino-1,3-butadiene (7) [derived from the initial opening of 3-nitro-4-(phenylsulfonyl)thiophene (6) with pyrrolidine and silver nitrate in EtOH] is revealed to be an excellent precursor of nitro(phenylsulfonyl) derivatives of ring-fused aromatic (naphthalene, phenanthrene) or heteroaromatic (benzothiophene) compounds whose substitution pattern cannot be easily achieved by conventional methods. The key step is represented by a thermal electrocyclic rearrangement of (E,E)-1-aryl-4-methylsulfonyl-2-nitro-3-phenylsulfonyl-1,3-butadienes (9), which, thanks to proper geometric and electronic factors, occurs in unprecedentedly mild conditions and is followed by an irreversible, concerted syn beta-elimination of methanesulfinic acid to aromatize the newly formed cyclohexadienic ring.

The structure of ethyl 5-methyl- 10-(2,4,6-trimethylphenyl)-8-oxa-1,2,9-triazabicyclo[5.3.0]deca-3,5,9-triene-2-carboxylate (I) has been determined. The 1,2-diazepine ring has a twisted-sofa form and the 1,2,4-oxadiazole ring has an envelope conformation, with the bridgehead C7 atom out of the plane of the ring. The terminal methyl group of the side chain is disordered, being split over two different positions

The gas-phase basicity of a number of alkyl 2,6-dialkylphenyl ketones (2,6-R2C6H3COR′) has been found to be almost insensitive to structural variations, as a result of a compensation of steric and electronic effects associated with the bulkiness and to the polarizability, respectively, of R and/or R′. On the contrary, the basicity in concentrated sulfuric acid undergoes, along the same series of compounds, a variation of nearly 8 pK units, as a consequence of steric inhibition of solvation of the protonated carbonyl as the main effect played by R and/or R′. The results in the condensed phase agree very nicely with recent findings relevant to some 4-substituted 2,6-dimethylacetophenones and 4-substituted acetophenones as well as with data for a large number of dialkyl or alkyl aryl ketones (either from the literature or determined herein) leading to an overall pKBH+ vs. m∗ correlation (slope=8.8, n=31, r=0.996; Eq. (3) ) which appears to be of general significance and identifies steric inhibition of solvation as a common prevailing factor influencing the carbonyl basicity, at least in the absence of strong conjugative interactions.

In the crystal structure of C12H11ClO, the (planar) mol­ecules give rise to a parallel packing. A model crystal obtained by semi-empirical and packing-energy calculations is consistent with the observed structure.

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.