Adriano Pizzabiocca
University of Camerino
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Featured researches published by Adriano Pizzabiocca.
Tetrahedron Letters | 1987
Paolo Crotti; Franco Macchia; Adriano Pizzabiocca; Gabriele Renzi; M. Speranza
Abstract The first experimental evidence for an entropy-driven frontside displacement in a gas-phase cationic nucleophilic substitution has been provided by the results concerning the ring opening of 1-phenylcyclohexene oxide catalized by gaseous acids.
Tetrahedron | 1991
Patrizio Cecchi; Marco Chini; Paolo Crotti; Adriano Pizzabiocca; Gabriele Renzi; Maurizio Speranza
Abstract The stereochemical outcome of the two diastereoisomeric rigid benzocondensed epoxides 2a and 2b in the acid-induced nucleophilic attack by MeOH in the gas-phase was studied and compared with the corresponding results obtained with the mobile epoxides of type 1. The stereochemistry of the ring opening process in these systems (1, 2a, b) appears to be dependent on the extent of the positive charge developed at the benzylic carbon. A rationalization which implies different benzylic carbocationic species is proposed, while the hypothesis of the intermediacy of fully developed benzylic carbenium ions does not appear to be supported by the present results.
Tetrahedron | 1989
Patrizio Cecchi; Adriano Pizzabiocca; Gabriele Renzi; Marco Chini; Paolo Crotti; Franco Macchia; Maurizio Speranza
Abstract Comparative analysis of the ratio of the isomeric monomethyl ethers of 1-arylcyclohexane-1,2-diols formed in the gas-phase and solvalytic acid-induced methanolysis of several 1-arylcyclohexene oxides indicates the intrinsic electronic factors determining the regio- and stereochemical course of the nucleophilic attack, related to the partial degree of carbocationic character at the reaction centre in the substitution transition state.
Tetrahedron | 1993
Marco Chini; Paolo Crotti; Filippo Minutolo; Emanuela Dezi; Antonietta Lombardozzi; Adriano Pizzabiocca; Gabriele Renzi
Abstract The effect of the aromatic ring substituents on the product distribution of the gas-phase acid-induced ring opening of benzocondensed epoxides 2a and 2b with MeOH was examined and compared with results from methanolysis. The observed syn/anti diastereoselectivity is strictly dependent on the type of the aromatic ring substituent (6-OCH3 or 7-Br), and a very satisfactory Hammett-type linear correlation was found for both epoxides. A razionalization of the results is given.
Tetrahedron Letters | 1983
Giorgio De Luca; Adriano Pizzabiocca; Gabriele Renzi
Abstract The reaction of diphenyl disulphide with 1,8-dehydronaphthalene gives benzo [kl] thioxantene(5), 1-naphthyl-phenyl-sulphide(6) and naphtho-[1,8-bc] thiet(7). Formation of these compounds is explained via the intermediacy of the radical species (8).
Journal of The Chemical Society-perkin Transactions 1 | 1980
Giorgio De Luca; Gabriele Renzi; Romano Cipollini; Adriano Pizzabiocca
The thermal decomposition of N-phenyl-N′-sulphinylhydrazine (1) in a number of solvents has been investigated. The isomeric composition of the biphenylic products indicates the intervention of phenyl radicals, which come from the homolysis of (1).
Tetrahedron | 1988
Patrizio Cecchi; Romano Cipollini; Adriano Pizzabiocca; Gabriele Renzi; Maurizio Sperasnza
Abstract The gas-phase pinacol rearrangement of cis and trans -1 -methyl-1,2-cyclohexanediols. promoted by D 3 + and C n H 5 + (n = 1,2), was studied by the radiolytic method in the pressure range 100–760 Torr. Under all conditions, 2-methyl-cyclohexanone is the predominant product, arising from both substrates via different pinacol rearrangements and successive fast isomerization of the corresponding primary intermediates, e.g. 0-protonated 1-methyl-1-cyclopentanecarboxaldehyde. This conclusion is based from kinetic analysis of competition experiments with pinacol as reference substrate, carried out at high pressure (760 Torr) with or without added base (NMe 3 , 3 Torr). showing that the pinacol rearrangement rates are markedly dependent on the stereochemical features of the diol. Accordingly the trans diol rearranges more rapidly than the cis isomer, which in turn isomerizes faster than pinacol, indicating that anti-periplanar CH 2 migration to the vicinal tertiary C-OH 2 + center in trans (k2) is over five times faster than H migration in cis (k3). Analysis Of the relative migrating ability of the different CH 2 moieties In trans (k2 > k1) allowed exclusion of appreciable anchimeric assistance in these gas-phase pinacol rearrangements. The results are compared with relevant gas-phase data and with those concerning the same substrates in acidic solution.
Tetrahedron Letters | 1983
Pierluigi Giacomello; Adriano Pizzabiocca; Gabriele Renzi; M. Speranza
Abstract Protonation by gaseous H + 3 , C n H + 5 (n=1,2), s-C 3 H + 7 and t-C 4 H + 9 cations promotes rearrangement of cyclopentane- and cyclohexanecarboxaldehyde to cyclohexanone and cyclopentylmethyl ketone, respectively. The reaction was investigated by radiolytic and mass spectrometric methods.
Journal of The Chemical Society, Chemical Communications | 1995
Emanuela Dezi; Antonietta Lombardozzi; Adriano Pizzabiocca; Gabriele Renzi; Maurizio Speranza
Gas phase nucleophilic substitution on oxygen-protonated but-1-en-3-ol and trans-but-2-en-1-ol by methanol proceeds via the concerted SN2′ mechanism in competition with the classical SN2 mechanism.
Journal of The Chemical Society, Chemical Communications | 1986
Paolo Crotti; Franco Macchia; Adriano Pizzabiocca; Gabriele Renzi; Maurizio Speranza
Complete regio- and stereo-selectivity has been observed in the gas phase acid-induced ring-opening of 1,2-epoxy-1-trimethylsilycyclohexane using two different nucleophiles (i.e. H2O and MeOH), which compares well with that of the same reaction carried out in solution.