Dario Landini

Tetrabutylammonium dihydrogentrifluoride: an efficient catalyst for regio and stereoselective conversion of epoxides to fluorohydrins under solid-liquid phase-transfer catalysis conditions.

Abstract Tetrabutylammonium dihydrogentrifluoride is an efficient and easy-to-handle hydrofluorinating agent in the ring-opening reaction of oxiranes to give good or excellent yields of fluorohydrins under solid-liquid PTC conditions.

Silicon polypodands: powerful metal cation complexing agents and solid-liquid phase-transfer catalysts of new generation

Abstract Silicon polypodands 5 – 7 are found to be powerful complexing agents of alkali metal salts in low polarity solvents and very efficient catalysts in anion-promoted reactions under solid–liquid PTC conditions. The catalytic activity is comparable with that of the cyclic polyether PHDB18C6 8 .

Phase transfer catalysis: some recent applications in organic synthesis

Abstract A survey dealing with the use of anhydrous potassium carbonate as an efficient base for promoting organic reactions under solid–liquid phase transfer catalysis (SL-PTC) conditions is reported. In particular, the generation in situ of trifluoro- and trichloroacetamidide, and reactions of these azaanions with 2-bromocarboxylic esters and epoxides, affording protected α-amino acids and β-amido alcohols, respectively, are described. The reduction of allylic nitroderivatives with CS 2 to oximes or nitriles under SL- and liquid–liquid PTC (LL-PTC) is also presented. Finally, new preparation methods and a study of the reactivity of quaternary onium fluorides, hydrogendifluorides and dihydrogentrifluorides, together with the use of dihydrogentrifluorides as hydrofluorinating agents under SL-PTC conditions, are reported.

Regioselective conversion of O-protected glycidols to fluorohydrins catalyuzed by tetrabutylammonium dihydrogentrifluoride under solid-liquid PTC conditions

Abstract A number of O-protected glycidols are regioselectively converted into the corresponding fluorohydrins FCH2CH(OH)CH2OX by reaction with catalytic amounts of Bu4N+H2F3- and a molar excess of KHF2. Most of the protective groups (X) examined are stable under the above conditions, moreover stereogenic carbons are not affected.

Synthesis of N-sulfonyl aziridines through regioselective opening of epoxides under solid-liquid PTC conditions

The ring opening of epoxides 1 with 4-toluenesulfonamide (6) under solid-liquid phase transfer catalysis (SL-PTC) conditions afforded regioselectively β-sulfonamidoalcohols 7 in high yields. These were further converted into N-sulfonylaziridines 9 after activation of the hydroxy leaving group followed by ring closing in the presence of potassium carbonate.

Phase transfer catalysis (PTC): search for alternative organic solvents, even environmentally benign

Abstract The use of aliphatic esters, ethers and ketones such as dimethyl carbonate (DMC), methyl-tert-amyl ether (MTAE), 5-methyl-2-hexanone (MIAK), 4-methyl-2-pentanone (MIBK) as an alternative to traditional solvents (toluene, chlorobenzene, etc.) was explored as a strategy for performing phase transfer catalyzed reactions in organic media, even environmentally benign. Experimental data show that in these media the partition of the catalyst in the organic phase is comparable or higher than that in chlorobenzene, especially in the case of scarcely lipophilic methyltributylammonium (3) or tetrabutylammonium (4) salts (Eq. (1)). Anion reactivity under PTC conditions increases with decreasing the solvent polarity, in the order: ketone

N-Monoalkylation of α-Amino Acid Esters under Solid-Liquid PTC Conditions

N-(2-Nitrophenylsulfonyl)- (o-NBS-AA-OMe, 4) and N-(4-Nitrophenylsulfonyl)-α-amino acid methyl esters (p-NBS-AA-OMe, 5) were N-alkylated with a variety of alkyl halides 6 under solid-liquid phase-transfer catalysis (SL-PTC) conditions, affording the alkylated products o-NBS-N-R2-AA-OMe 7 and p-NBS-N-R2-AA-OMe 8 in excellent yields without any detectable racemization.

Complementary heterogeneous/homogeneous protocols for the synthesis of densely functionalized benzo[d]sultams: C-C bond formation by intramolecular nucleophilic aromatic fluorine displacement.

Polyfunctionalized benzo[d]sultams 7 and 8, which contain an alpha-amino acid unit, have been synthesized from the corresponding open chain (pentafluorobenzene)sulfonamides 4 by complementary solid-liquid phase transfer catalysis (SL-PTC) and homogeneous protocols. The cyclization step proceeds through the intramolecular nucleophilic displacement of an aromatic fluorine atom.

Catalytic activity and anion activation in SN2 reactions promoted by complexes of silicon polypodands. Comparison with traditional polyethers

The catalytic activity of silicon polypodands was evaluated in anion-promoted reactions under solid–liquid phase-transfer catalysis (SL-PTC) conditions and compared with that exhibited by common PTC agents. Results showed that these many-armed ligands are particularly efficient catalysts, even comparable with the more sophisticated crown ethers. Kinetics under homogeneous conditions indicated that the anion activation realized by silicon polypodands does not appreciably change with the number of chains and is comparable or slightly lower than that of traditional polyethers. In addition, the sequence of reactivity is determined by the cation (NH4+ < K+ < Na+ < Li+), thus revealing an involvement of the metal ion in the transition state of the reactions (“metal ion electrophilic catalysis”).

Regioselective opening of epoxides to β-amido alcohols under solid-liquid PTC conditions

Abstract A study on the ring opening of a number of epoxides 1 with trifluoroacetamide ( 2 ) under solid-liquid phase transfer catalysis (SL-PTC) conditions has been performed. The reaction is completely regioselective affording β-amido alcohols 3 deriving from the attack of the nucleophile to the less substituted carbon atom of the oxirane ring.