Loris Grossi - Academia.edu (original) (raw)
Papers by Loris Grossi
The Journal of Organic Chemistry, 1984
oxide is a white solid and was recrystallized from C14CfMeOH (W10): mp 180-186 OC; NMR S (Cl,C/Me... more oxide is a white solid and was recrystallized from C14CfMeOH (W10): mp 180-186 OC; NMR S (Cl,C/Me4Si) 5.3 (8, 1 H) 6.4-7.6 (m, 22 H); MS, m/e (relative intensity) 454 (23), 453 (13), 252 (15), 216 (loo), 201 (51), 124 (23), 77 (52), 51 (15). Photostimulated Reaction of Diphenylphosphide Ion with 9-Bromotriptycene in the Presence of Inhibitors. The procedure was similar to that for the previous reactions, except that in expt 4 (Table I) 20 mol % of p-dinitrobenzene was added and in expt 3 (Table I) 10 mol % of di-tert-butyl nitroxide was added. Photostimulated Reaction of 9-Bromotriptycene with Diphenylarsenide ion. The procedure was similar to that for the previous reaction, except that the irradiation time was 60 min. The residue of the ether extract was column chromatographed on silica gel and eluted with petroleum ether. The product isolated was 9-triptycyldiphenylarsine, recrystallized from benzene: mp 242-246 O C ; NMR (C14C/Me4Si) 5.4 (8, 1 H), 6.5-7.6 (m, 22 H); MS, mfe (relative intensity) 483 (lo), 482 (80), 320 (28), 253.4 (loo), 227 (43), 152 (20), 77 (5), 51 (5). Photostimulated Reaction of 9,lO-Dibromotriptycene with Diphenylphosphide Ion. The procedure was similar to that for the previous reaction. The reaction mixture was extracted as was described. The ethereal extract was oxidized with hydrogen peroxide, and the 9,1O-bis(diphenylphosphinyl)triptycene produced was recrystallized from chloroformfpetroleum ether (50:50): mp 325 O C ; NMR 6 7-7.4 (m); MS, mfe (relative intensity) 655 (35), 454 (ll), 453 (45), 252 (42), 202 (16), 201 (loo), 185 (14). Acknowledgment. Sara M. Palacios gratefully acknowledges receipt of a felloyship from the Consejo Nacional de Investigaciones Cientificas y TBcnicas, Argentina. INFIQC is jointly spcnsored by the Consejo Nacional de Investigaciones Cientificas y TBcnicas and the Universidad Nacional de Cdrdoba This work is partially supported by the SUBCYT. Professor James F. Wolfe is thanked for the gift of a sample of di-tert-butyl nitroxide.
Journal of the Chemical Society, Perkin Transactions 2, 1981
ABSTRACT
J. Chem. Soc., Perkin Trans. 2, 1986
ABSTRACT
Tetrahedron Letters, 1992
Journal of the Chemical Society, Perkin Transactions 2, 1980
ABSTRACT
Tetrahedron, 1994
Abstract The oxidation reaction of aniline by tertiary hydroperoxides, induced photochemically, w... more Abstract The oxidation reaction of aniline by tertiary hydroperoxides, induced photochemically, was studied. The peculiar radical intermediates, nitroxides and peroxy radicals, involved in the reaction mechanism were detected and identified by EPR spectroscopy. The presence of these intermediates confirm that PhNO is the first product of the oxidation of aniline and the PhNH· radical as its precursor.
Tetrahedron, 1997
ABSTRACT
Tetrahedron, 1986
Abetract. The reaction of Z-lithio-1,3-dithianes with nitroarenes gives 2-(or 4-)[(1,3-dithian)-2... more Abetract. The reaction of Z-lithio-1,3-dithianes with nitroarenes gives 2-(or 4-)[(1,3-dithian)-2*-yl]cyclohexa_3,5(or 2,5-)-diene-l-nitronate compounds (conjugate-addition products), free nitroarene radical anions (redox products), 1,3-dithianes and 2,2'-bis-(1,3-dithianes). The ccnjugate-addition and redox products were converted in the respective nitroaromatic compounds by oxidation in situ with 0 2 or DDQ. The ratio between addition and redox products increases with decrease of temperature. 2-H-2-Lithio-1,3-dithiane can give both 1.4-and 1.6~addition products, while P-methyl-and 2-phenyl derivatives give only 1.6-addition products. A mechanism involving an s.e.t. from lithium dithianes to nitroarenes followed by various decay routes is suggested for the two radical species. The introduction of a masked carbonylic function into an activated aromatic ring by using 1,3dithiane-anions represents an imortant goal in organic chemistry; however, this synthetic strategy has shown serious unresolved problems. 1 Lithium-dithianes are reported to give addition to 2-bromopyridine, but redox on mono-and dinitr+halobenzenes. 2 Recently, mechanistic investigations on factors affecting reaction product distribution has led to correct some erroneous opinions on the action of carbanions toward strong electron-acceptor substrates. 3 A significant example is represented by the conjugate-addition of alkyl Grignard reagents to mononitroarenic systems, recently discovered. 4 These remarks led us to investigate on the possibility to observe conjugate-addition also in the reaction of lithium dithianes with mononitroarenes. At variance with previous reports, the reaction of 4-chloronitrobenzene (1) with 2-lithio-1,3dithiane (2a), in THF at 40°C, gives large amounts of 1,4-addition product (48). together with free 4-chloronitrobenzene radical anion (31, 1,3-dithiane (5a) and 2,2'-bis-(1,3-dithiane) (Se) (see Scheme I). The decomposition of the reaction mixture with NH4Cl allowed to isolate the following compounds: l-chlorc-3-[(1,3-dithian)-2'-yl]4-nitrobenzene (&; 19.5% yields) and its correspondent azoxy compound 7a (18.5%) (i.e. the disproportions&ion products of the unstable nitronate adduct 4a)i4 the starting nitroarene 1 (26.5%) and its correspondent azoxy derivative 9 (18.5%) (i.e. the disproportionation products of the radical anion 3); 5 1,3-dithiane (19%) and bis-dithiane 8a (20%). The global yields accounted for the Box and the 70% of the reactants 1 and 2r respectively.
Tetrahedron, 1993
Abstract The 4′-substituted N-methylbenzenesulfenanilides 1a–c react with Lewis acids, including ... more Abstract The 4′-substituted N-methylbenzenesulfenanilides 1a–c react with Lewis acids, including BF3, AlCl3 and GaCl3, to afford the radical cation intermediates 9a–c, some of which could be detected by e.p.r. spectroscopy. Thus, the 4′-methoxy substituted compound 1a gave the fairly persistent radical cation 9a. In contrast, the radical cation 9b, derived from the 4′-nitro substituted compound 4b, was not detected apparently because it decayed too rapidly forming the very stable radical cation 11b, intermediate in the formation of the rearranged sulfide 10b. The radical intermediates 9a–c react with cyclohexene to give the 1,2-adducts 4a–c, 5 and 6 which are believed to be formed from either the thiiranium ion 7b or the sulfurane 8a,c.
Tetrahedron, 2012
ABSTRACT Eight simple amides have been subjected to UV irradiation in the presence of either MNP ... more ABSTRACT Eight simple amides have been subjected to UV irradiation in the presence of either MNP or NO. In all cases radical species were generated: these were detected by means of EPR spectroscopy in the form of different nitroxides resulting from the trapping of the primary radicals. NO acted as a double spin trap, scavenging a radical to afford a diamagnetic nitroso derivative that in turn acted as trap towards another radical unit. As amido-groups are present in components of skin tissue and may be present in many therapeutic or cosmetic products used as skin sunscreen, and NO is a ubiquitous endogenous reactive species, the nitroxides detected in the present studies might participate in radical processes triggered by sun exposure and resulting in damages, even severe, of biological tissues.
Research on Chemical Intermediates, 1993
Molecular and Cellular Biochemistry, 1996
Acetylcholine-induced, endothelium-dependent relaxation ofnorepinephrine-precontracted aortic str... more Acetylcholine-induced, endothelium-dependent relaxation ofnorepinephrine-precontracted aortic strips, was severely impaired after exposure to a hypoxanthine/xanthine oxidase reaction generating oxygen radicals. This effect was more evident in aortic strips of aging rats (24 months old) in comparison to young rats (3 months old). The addition of authentic .NO (1 j~M) completely relaxed aortic strips exposed to oxidative stress both in young and aging rats. In vitro EPR measurements showed that the-NO signal was reduced by enzymatic 02 = generating reaction. The activity of a partial purified preparation of constitutive NO synthase from rat cerebellum was significantly decreased after exposure to exogenous oxygen radicals. Pretreatment of aortic strips with 100 laM alpha-tocopherol-phosphate, produced a significant improvement ofacetylcholine-dependent relaxation in the aortic strips exposed to oxidative stress, particularly in the aged vessel. The content of malondialdehyde in aortic tissue did not change after oxidative stress or alpha-tocopherol pretreatment. Alpha-tocopherol was unable to recover the NO synthase activity depressedin vitro by hypoxanthine/xanthine oxidase reaction. This study confirms that an oxidative stress impairs the endothelium-mediated vasodilation. Alpha-tocopherol pretreatment protects the vessel against this damage. The mechanism of action of alpha-tocopherol is unknown, but seems unrelated to an antioxidant activity.
Journal of the American Chemical Society, 2001
The Journal of Organic Chemistry, 1998
The Journal of Organic Chemistry, 1985
The Journal of Organic Chemistry, 1986
piperidine is reported42 to be 37 ppm. Cf. PhNHNHz for which the shifts are 87 and 62 ppm, re~pec... more piperidine is reported42 to be 37 ppm. Cf. PhNHNHz for which the shifts are 87 and 62 ppm, re~pectively.~~ The mass spectrum was obtained by GC/MS, m / e (a) 185 (19), 170 (lo), 129 (7), 127 (7), 113 (9), 112 (loo), 87 (14), 85 (7), 84 (44), 83 (lo), 82 (22), 74 (17), 68 (6). After 4 days, only 4-piperidinecarboxamide (3) was detected by gas chromatography. It was identified by using an authentic standard. Reduction of Isoniazid. Isoniazid (1) was reduced as above, and 4-piperidinecarboxylic acid hydrazide (2) was identified by GC/MS as an intermediate after 6.3 h: MS, m/e (%) 143 (lo),
Inorganic Chemistry, 1993
ABSTRACT
European Journal of Organic Chemistry, 2001
ABSTRACT Reactions of peroxynitrous acid, HPN, with styrene under acidic conditions lead to the o... more ABSTRACT Reactions of peroxynitrous acid, HPN, with styrene under acidic conditions lead to the oxime 1, the nitrate 2, benzaldehyde (3), and α-nitroacetophenone (4) in overall yields that depend strongly on the pH value and with a product distribution that depends on the dioxygen concentration. The results are rationalized by assuming that HPN undergoes acid-catalyzed decomposition to give nitrous anhydride, or its synthetic equivalent, which is responsible for the regioselective nitration of the styrene double bond by an ET process. The resulting β-nitrobenzyl radical 6 can, depending on the reaction conditions, undergo reversible coupling with nitric oxide to afford the nitroso derivative 7 and then the tautomeric oxime 1, or trapping by dioxygen, eventually leading to products 2, 3, and 4 through the intermediacy of the peroxynitrite derivative 8. Oxime 1 and nitrate 2 are also obtained by treating styrene with nitrous anhydride under protic conditions, the latter being produced in situ from nitric oxide/dioxygen. Similarly to styrene, 1,4-diphenylbutadiene (14) gives radicals 22 and 21 by competitive trapping at the side chain and at the aromatic ring. In turn, radicals 22 and 21 undergo β-fragmentation reactions or trapping by dioxygen with eventual formation of nitrates 16 and 17, cinnamic aldehyde (18), and the diol 15. Finally, the HPN-promoted reaction of p-cresol (27) leads to the 2-nitro derivative 28 through an initial electron-transfer process followed by in cage recombination of the resulting radical ion pair.
Chemistry - A European Journal, 2002
The Journal of Organic Chemistry, 1984
oxide is a white solid and was recrystallized from C14CfMeOH (W10): mp 180-186 OC; NMR S (Cl,C/Me... more oxide is a white solid and was recrystallized from C14CfMeOH (W10): mp 180-186 OC; NMR S (Cl,C/Me4Si) 5.3 (8, 1 H) 6.4-7.6 (m, 22 H); MS, m/e (relative intensity) 454 (23), 453 (13), 252 (15), 216 (loo), 201 (51), 124 (23), 77 (52), 51 (15). Photostimulated Reaction of Diphenylphosphide Ion with 9-Bromotriptycene in the Presence of Inhibitors. The procedure was similar to that for the previous reactions, except that in expt 4 (Table I) 20 mol % of p-dinitrobenzene was added and in expt 3 (Table I) 10 mol % of di-tert-butyl nitroxide was added. Photostimulated Reaction of 9-Bromotriptycene with Diphenylarsenide ion. The procedure was similar to that for the previous reaction, except that the irradiation time was 60 min. The residue of the ether extract was column chromatographed on silica gel and eluted with petroleum ether. The product isolated was 9-triptycyldiphenylarsine, recrystallized from benzene: mp 242-246 O C ; NMR (C14C/Me4Si) 5.4 (8, 1 H), 6.5-7.6 (m, 22 H); MS, mfe (relative intensity) 483 (lo), 482 (80), 320 (28), 253.4 (loo), 227 (43), 152 (20), 77 (5), 51 (5). Photostimulated Reaction of 9,lO-Dibromotriptycene with Diphenylphosphide Ion. The procedure was similar to that for the previous reaction. The reaction mixture was extracted as was described. The ethereal extract was oxidized with hydrogen peroxide, and the 9,1O-bis(diphenylphosphinyl)triptycene produced was recrystallized from chloroformfpetroleum ether (50:50): mp 325 O C ; NMR 6 7-7.4 (m); MS, mfe (relative intensity) 655 (35), 454 (ll), 453 (45), 252 (42), 202 (16), 201 (loo), 185 (14). Acknowledgment. Sara M. Palacios gratefully acknowledges receipt of a felloyship from the Consejo Nacional de Investigaciones Cientificas y TBcnicas, Argentina. INFIQC is jointly spcnsored by the Consejo Nacional de Investigaciones Cientificas y TBcnicas and the Universidad Nacional de Cdrdoba This work is partially supported by the SUBCYT. Professor James F. Wolfe is thanked for the gift of a sample of di-tert-butyl nitroxide.
Journal of the Chemical Society, Perkin Transactions 2, 1981
ABSTRACT
J. Chem. Soc., Perkin Trans. 2, 1986
ABSTRACT
Tetrahedron Letters, 1992
Journal of the Chemical Society, Perkin Transactions 2, 1980
ABSTRACT
Tetrahedron, 1994
Abstract The oxidation reaction of aniline by tertiary hydroperoxides, induced photochemically, w... more Abstract The oxidation reaction of aniline by tertiary hydroperoxides, induced photochemically, was studied. The peculiar radical intermediates, nitroxides and peroxy radicals, involved in the reaction mechanism were detected and identified by EPR spectroscopy. The presence of these intermediates confirm that PhNO is the first product of the oxidation of aniline and the PhNH· radical as its precursor.
Tetrahedron, 1997
ABSTRACT
Tetrahedron, 1986
Abetract. The reaction of Z-lithio-1,3-dithianes with nitroarenes gives 2-(or 4-)[(1,3-dithian)-2... more Abetract. The reaction of Z-lithio-1,3-dithianes with nitroarenes gives 2-(or 4-)[(1,3-dithian)-2*-yl]cyclohexa_3,5(or 2,5-)-diene-l-nitronate compounds (conjugate-addition products), free nitroarene radical anions (redox products), 1,3-dithianes and 2,2'-bis-(1,3-dithianes). The ccnjugate-addition and redox products were converted in the respective nitroaromatic compounds by oxidation in situ with 0 2 or DDQ. The ratio between addition and redox products increases with decrease of temperature. 2-H-2-Lithio-1,3-dithiane can give both 1.4-and 1.6~addition products, while P-methyl-and 2-phenyl derivatives give only 1.6-addition products. A mechanism involving an s.e.t. from lithium dithianes to nitroarenes followed by various decay routes is suggested for the two radical species. The introduction of a masked carbonylic function into an activated aromatic ring by using 1,3dithiane-anions represents an imortant goal in organic chemistry; however, this synthetic strategy has shown serious unresolved problems. 1 Lithium-dithianes are reported to give addition to 2-bromopyridine, but redox on mono-and dinitr+halobenzenes. 2 Recently, mechanistic investigations on factors affecting reaction product distribution has led to correct some erroneous opinions on the action of carbanions toward strong electron-acceptor substrates. 3 A significant example is represented by the conjugate-addition of alkyl Grignard reagents to mononitroarenic systems, recently discovered. 4 These remarks led us to investigate on the possibility to observe conjugate-addition also in the reaction of lithium dithianes with mononitroarenes. At variance with previous reports, the reaction of 4-chloronitrobenzene (1) with 2-lithio-1,3dithiane (2a), in THF at 40°C, gives large amounts of 1,4-addition product (48). together with free 4-chloronitrobenzene radical anion (31, 1,3-dithiane (5a) and 2,2'-bis-(1,3-dithiane) (Se) (see Scheme I). The decomposition of the reaction mixture with NH4Cl allowed to isolate the following compounds: l-chlorc-3-[(1,3-dithian)-2'-yl]4-nitrobenzene (&; 19.5% yields) and its correspondent azoxy compound 7a (18.5%) (i.e. the disproportions&ion products of the unstable nitronate adduct 4a)i4 the starting nitroarene 1 (26.5%) and its correspondent azoxy derivative 9 (18.5%) (i.e. the disproportionation products of the radical anion 3); 5 1,3-dithiane (19%) and bis-dithiane 8a (20%). The global yields accounted for the Box and the 70% of the reactants 1 and 2r respectively.
Tetrahedron, 1993
Abstract The 4′-substituted N-methylbenzenesulfenanilides 1a–c react with Lewis acids, including ... more Abstract The 4′-substituted N-methylbenzenesulfenanilides 1a–c react with Lewis acids, including BF3, AlCl3 and GaCl3, to afford the radical cation intermediates 9a–c, some of which could be detected by e.p.r. spectroscopy. Thus, the 4′-methoxy substituted compound 1a gave the fairly persistent radical cation 9a. In contrast, the radical cation 9b, derived from the 4′-nitro substituted compound 4b, was not detected apparently because it decayed too rapidly forming the very stable radical cation 11b, intermediate in the formation of the rearranged sulfide 10b. The radical intermediates 9a–c react with cyclohexene to give the 1,2-adducts 4a–c, 5 and 6 which are believed to be formed from either the thiiranium ion 7b or the sulfurane 8a,c.
Tetrahedron, 2012
ABSTRACT Eight simple amides have been subjected to UV irradiation in the presence of either MNP ... more ABSTRACT Eight simple amides have been subjected to UV irradiation in the presence of either MNP or NO. In all cases radical species were generated: these were detected by means of EPR spectroscopy in the form of different nitroxides resulting from the trapping of the primary radicals. NO acted as a double spin trap, scavenging a radical to afford a diamagnetic nitroso derivative that in turn acted as trap towards another radical unit. As amido-groups are present in components of skin tissue and may be present in many therapeutic or cosmetic products used as skin sunscreen, and NO is a ubiquitous endogenous reactive species, the nitroxides detected in the present studies might participate in radical processes triggered by sun exposure and resulting in damages, even severe, of biological tissues.
Research on Chemical Intermediates, 1993
Molecular and Cellular Biochemistry, 1996
Acetylcholine-induced, endothelium-dependent relaxation ofnorepinephrine-precontracted aortic str... more Acetylcholine-induced, endothelium-dependent relaxation ofnorepinephrine-precontracted aortic strips, was severely impaired after exposure to a hypoxanthine/xanthine oxidase reaction generating oxygen radicals. This effect was more evident in aortic strips of aging rats (24 months old) in comparison to young rats (3 months old). The addition of authentic .NO (1 j~M) completely relaxed aortic strips exposed to oxidative stress both in young and aging rats. In vitro EPR measurements showed that the-NO signal was reduced by enzymatic 02 = generating reaction. The activity of a partial purified preparation of constitutive NO synthase from rat cerebellum was significantly decreased after exposure to exogenous oxygen radicals. Pretreatment of aortic strips with 100 laM alpha-tocopherol-phosphate, produced a significant improvement ofacetylcholine-dependent relaxation in the aortic strips exposed to oxidative stress, particularly in the aged vessel. The content of malondialdehyde in aortic tissue did not change after oxidative stress or alpha-tocopherol pretreatment. Alpha-tocopherol was unable to recover the NO synthase activity depressedin vitro by hypoxanthine/xanthine oxidase reaction. This study confirms that an oxidative stress impairs the endothelium-mediated vasodilation. Alpha-tocopherol pretreatment protects the vessel against this damage. The mechanism of action of alpha-tocopherol is unknown, but seems unrelated to an antioxidant activity.
Journal of the American Chemical Society, 2001
The Journal of Organic Chemistry, 1998
The Journal of Organic Chemistry, 1985
The Journal of Organic Chemistry, 1986
piperidine is reported42 to be 37 ppm. Cf. PhNHNHz for which the shifts are 87 and 62 ppm, re~pec... more piperidine is reported42 to be 37 ppm. Cf. PhNHNHz for which the shifts are 87 and 62 ppm, re~pectively.~~ The mass spectrum was obtained by GC/MS, m / e (a) 185 (19), 170 (lo), 129 (7), 127 (7), 113 (9), 112 (loo), 87 (14), 85 (7), 84 (44), 83 (lo), 82 (22), 74 (17), 68 (6). After 4 days, only 4-piperidinecarboxamide (3) was detected by gas chromatography. It was identified by using an authentic standard. Reduction of Isoniazid. Isoniazid (1) was reduced as above, and 4-piperidinecarboxylic acid hydrazide (2) was identified by GC/MS as an intermediate after 6.3 h: MS, m/e (%) 143 (lo),
Inorganic Chemistry, 1993
ABSTRACT
European Journal of Organic Chemistry, 2001
ABSTRACT Reactions of peroxynitrous acid, HPN, with styrene under acidic conditions lead to the o... more ABSTRACT Reactions of peroxynitrous acid, HPN, with styrene under acidic conditions lead to the oxime 1, the nitrate 2, benzaldehyde (3), and α-nitroacetophenone (4) in overall yields that depend strongly on the pH value and with a product distribution that depends on the dioxygen concentration. The results are rationalized by assuming that HPN undergoes acid-catalyzed decomposition to give nitrous anhydride, or its synthetic equivalent, which is responsible for the regioselective nitration of the styrene double bond by an ET process. The resulting β-nitrobenzyl radical 6 can, depending on the reaction conditions, undergo reversible coupling with nitric oxide to afford the nitroso derivative 7 and then the tautomeric oxime 1, or trapping by dioxygen, eventually leading to products 2, 3, and 4 through the intermediacy of the peroxynitrite derivative 8. Oxime 1 and nitrate 2 are also obtained by treating styrene with nitrous anhydride under protic conditions, the latter being produced in situ from nitric oxide/dioxygen. Similarly to styrene, 1,4-diphenylbutadiene (14) gives radicals 22 and 21 by competitive trapping at the side chain and at the aromatic ring. In turn, radicals 22 and 21 undergo β-fragmentation reactions or trapping by dioxygen with eventual formation of nitrates 16 and 17, cinnamic aldehyde (18), and the diol 15. Finally, the HPN-promoted reaction of p-cresol (27) leads to the 2-nitro derivative 28 through an initial electron-transfer process followed by in cage recombination of the resulting radical ion pair.
Chemistry - A European Journal, 2002