Organocatalysts and metal-based catalysts: a journey toward the development of new catalytic materials

Organocatalysis and metal-based catalysis represent two of the main pillars of catalytic reactions and have witnessed a huge interest in the last decade. Immobilization, recovery and reuse of these catalysts is of primary importance because of the large amount used especially in the case of organocatalysts. On the other hand, metal-based catalysts must be recovered even if used in low amount, in order to avoid contamination of the product. In this context, we started several years ago investigations on the use of supported ionic liquid phases for the asymmetric organocatalysis mediated by proline.1 This approach is an example of a “release and catch” catalytic system.2 Starting from this example, we describe the development of new catalytic materials based on the use of i) supported ionic liquid phase (Scheme 1a) ii) covalently linked catalysts (scheme 1b) iii) ionic liquid-modified fullerenes (Scheme 1c), with the goal to obtain recyclable catalytic materials for C-C coupling reactions and alcohols oxidation.3 These studies have paved the way for the development of new hybrid materials such as silica-fullerenes or CNT-IL or POSS-IL

Organocatalizzatori e liquidi ionici supportati: nuovi materiali in sintesi organica

Nell’ultimo decennio l’organocatalisi e i liquidi ionici hanno rappresentato due campi di grande interesse scientifico. Gli organocatalizzatori hanno trovato particolare impiego in sintesi enantioselettive conducendo a prodotti finali con alte rese e selettività. I liquidi ionici sono stati estensivamente utilizzati come solventi alternativi e, opportunamente modificati, come catalizzatori o loro supporti. Uno sviluppo attuale che accomuna questi due campi di ricerca consiste nella possibilità di immobilizzazione di organocatalizzatori e liquidi ionici per trasformarli in materiali riciclabili con ampie capacità di utilizzo in chimica organica. Negli ultimi anni, il nostro gruppo di ricerca si è occupato di organocatalizzatori e liquidi ionici supportati. E’ stata sviluppata una metodologia sintetica per l’ancoraggio di organocatalizzatori su resine polistireniche attraverso una reazione tiolo-ene, permettendo di ottenere un largo numero di materiali catalitici che sono stati impiegati in reazioni aldoliche, di -selenenilazione e di Michael (Figura 1).1-2 Nel campo dei liquidi ionici supportati (SILP) ci siamo occupati del loro uso nel campo delle reazioni catalizzate da metalli che in organocatalisi. Inoltre, i SILP sono stati efficacemente impiegati in reazioni di apertura di epossidi in CO2 supercritica per fornire carbonati ciclici.3-4 In questo campo abbiamo sviluppato due tipi di materiali, monostrato e multistrato (Figura 2)

A competitive reactivity study on the oxidative cyclization of thiosemicarbazones into 1,3,4-thiadiazolidines

Abstract In order to obtain useful insights on the mechanism of formation of 2(3H)-imino-1,3,4-thiadiazoles by oxidative cyclization of aldehyde thiosemicarbazones with Cu(II) or Fe(III) salts, a competitive reactivity study was performed on a suitable set of diversely substituted substrates, by means of HPLC techniques. This approach enabled to exploit Hammett\u2019s equation without performing otherwise difficult-to-run kinetic experiments. The results presented herein support the hypothesis that the formation of the thiadiazole ring is induced by the attack of the oxidizing Lewis acid metal cation onto the imine-like nitrogen atom of the thiosemicarbazone substrate. Beyond mechanistic interpretation, the paper particularly focuses onto the methodological issues implied

Lipase-catalyzed resolution of anti-substituted 1,3-dioxepan-5-ols

Several anti-6-substituted 1,3-dioxepan-5-ols were kinetically resolved using an immobilized lipase (Amano PS–C II) in toluene in the presence of vinyl acetate at 30 C. This approach provided, in some cases, the alcohol and the acetate in high enantiomeric purity, depending on the nature of the substituent (R = N3, SePh, I, OBn) and the acetal group (unsubstituted or dimethyl). The role of the size of substituents is also discussed. Enantiopure anti-6-substituted 1,3-dioxepan-5-ols are useful building blocks