Reazioni di vari reagenti elettrofili con derivati amminotiazolici ad elevato potere nucleofilo

The nucleophile/electrophile combination in the aromatic substitution reaction using aminothiazole derivatives as nucleophiles has been the subject of this study. The reaction between 2,4-dipyrrolidinylthiazole and the neutral carbon electrophile 1,3,5-trinitrobenzene gave a stable Wheland-Meisenheimer (WM) complex. This represents another example, among those already found by the research group in which this work has been carried out, of stable zwitterionic σ-intermediates. When the reaction was carried out with halonitrobenzene derivatives, it produced the substitution product in position 5 of the thiazole ring. 2,4-dipyrrolidinylthiazole and arenediazonium salts gave the coupling product at the C5 of the thiazole ring together with many byproducts and the stable Wheland intermediate formed by attack of the proton on the C5 of the starting thiazole reagent. Arenediazonium salts were coupled also with 2-pyrrolidinylthiazole. In this case quantitative formation of the substitution product deriving from the attack of the electrophile on the carbon nucleophilic position of the thiazole ring was obtained. In conclusion, the results had allowed to expand the knowledge on electrophilic/nucleophilic interactions in the aromatic substitution involving thiazole heteroaromatics and provided a further example of stable Wheland-Meisenheimer intermediates.

Studio approfondito di processi post-polimerizzazione del poli(glicidil metacrilato)

The reactivty of poly(glycidyl methacrylate), obtained by RAFT controlled radical polymerization, has been investigated with a nucelophilic agent, such as morpholine, in various aprotic polar solvents in order to optimize the reaction (time and nucleophile excess). A strong interaction between polymer and solvent, gained by hydrogen bonds, during the process has proved to be essential in order to lower the reaction time and the nucelophilic agent excess. Dissimilar behaviors have been detected by GPC analysis due to the reactivity of the sulfhydryl formed during the RAFT's aminolysis. The various solvents lead to conditions in which different inter and intra-chain associations occur; the result is the formation of dimers, trimers and tetramers (to a less extent) in the first case, and cyclical structures in the second one. The reactivity of the hydroxy group, formed during the ring opening reaction, has been further investigated in order to link isothiocyanate-functionalized fluorescent marker along the polymeric chain.

Dearomatizzazione organocatalitica regio- ed enantioselettiva di sali di piridinio attivati

In this work, we present the first regio- and enantioselective organocatalytic nucleophilic dearomatization of activated N-alkyl pyridinium salts. In particular, N-benzyl pyridinium bromides bearing electron-withdrawing substituents at the C3 position of the pyridine ring were chosen as substrates. These compounds were easily obtained through an alkylation reaction between benzyl bromides and the corresponding 3-substituted pyridines. Then, a wide range of nucleophiles and organocatalysts was tested, providing the best results when indole, a thiourea derived from quinidine and 1-benzyl-3-nitropyridinum bromide were employed as the nucleophile, the catalyst and the pyridinium salt, respectively. Subsequently, the reaction conditions were optimised evaluating different bases, solvents, N-benzylic protecting groups, molar concentrations and temperatures. With the optimized condition in hand, the scope of the reaction with different substituted indoles was explored, affording the corresponding 1,4-dihydropyridines in good yields, regio- and enantio-selectivities. In addition, several experiments were carried out in order to understand the mechanism of the reaction, showing an unusual pathway involving a covalently bound intermediate formed by addition of the catalyst to the pyridine unit.