2020, Articolo in rivista, ENG
Casiello M.; Caputo D.; Fusco C.; Cotugno P.; Rizzi V.; Dell'Anna M.M.; D'Accolti L.; Nacci A.
Unprecedented in literature, the conversion of aryl alkenes into ?-nitrostyrenes (2) or benzonitriles (3) with sodium nitrite can be governed by an appropriate choice of ionic liquid (IL) medium. A general trend was found for the selectivity of these processes, which depends on the nature of IL, with imidazolium-based ILs, such as [Bmim]Cl, that favor the C-H nitration leading to ?-nitrostyrenes, while tetraalkylammonium-based ILs, such as TBAA, privilege the C=C bond cleavage affording benzonitriles. Besides a substrate scope, mechanistic hypotheses were provided on the origin of the different selectivity in the two kinds of ILs, based on their own tunable properties such as polarity, viscosity, and solvent cage effects.
2016, Articolo in rivista, ENG
Baglieri A.; Meschisi L.; De Sarlo F.; Machetti F.
Isoxazoles, mainly 3,5-disubstituted, are prepared by catalytic condensation of primary nitro compounds with terminal acetylenes by using a copper/base catalytic system. The additional catalytic effect of the copper(II) salts is evidenced by comparing the kinetic profiles. Selectivity dependence on reaction conditions is considered for phenylacetylene in the following competitive processes: oxidative coupling of terminal alkynes to conjugated diynes catalyzed by CuII and base in the presence of air; production of furazans beside condensation with benzoylnitromethane to 3-benzoylisoxazoles, as a result of the reaction of the dipolarophile with 3,4-dibenzoylfuroxan; addition of electron-poor alkynes (e.g., methyl propiolate) with themselves and with the nitro compound. Thus, oxidative coupling is negligible in reactions with "active" nitro compounds, whereas with nitroalkanes both products are observed: only trace amounts of isoxazoles are detected without copper. Similarly, in the presence of copper, 3-benzoyl-5-phenylisoxazole is predominant over the furazan. Furthermore, condensations of electron-poor alkynes give complex reaction mixtures in the presence of base alone, but cycloadducts are conveniently prepared with copper. The results indicate the practical and general utility of this catalytic method for synthetic practice.
2014, Articolo in rivista, ENG
Biagiotti, Giacomo; Cicchi, Stefano; De Sarlo, Francesco; Machetti, Fabrizio
The catalysed condensation of [60]fullerene with ethyl nitroacetate (1b) or analogous activated nitro derivatives to afford isoxazolino[60]fullerenes has been achieved in both homogeneous and heterogeneous conditions. This direct synthetic approach is more convenient than previous methods. Model reactions with electron-poor dipolarophiles led to either condensation to isoxazolines or to conjugate addition products, depending on the nitro compound and catalyst. The former product was favoured by the use of CuII in the catalytic system. Conversely, [60]fullerene underwent catalytic condensation, even in the absence of copper(II) salts, only with activated nitro compounds and addition only with nitroalkanes in excess base. Note, the formal conjugated fullerene addition product was obtained in isomeric form, as previously reported. A possible explanation is presented for this contrasting behaviour.
2009, Articolo in rivista, ENG
Trogu, Elena; Cecchi, Luca; De Sarlo, Francesco; Guideri, Luca; Ponticelli, Fabio; Machetti, Fabrizio
Primary nitro compounds have not been employed as nitrile oxide precursors in reactions with active methylene compounds because the reagents commonly used as dehydrating agents also react with these dipolarophiles. However, the Cull-catalysed cycloaddition/condensation procedure has been shown to be viable with these substrates, leading directly to the expected polyfunctional isoxazoles provided nitro compounds with enhanced acidity ("activated") were used. In the absence of added dipolarophiles, these nitro compounds underwent self-condensation to the corresponding furoxans. However, as well as 3,4-dibenzoylfuroxan, benzoylnitromethane predominantly gave the isomer 3-benzoyl-4-nitro-5-phenylisoxazole, the structure of which was confirmed by crystallographic analysis.