Michele Penso

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.

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.

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.

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.

One-Pot Conversion of Allylic Nitro Compounds into Nitriles with Carbon Disulphide Under Phase-Transfer Catalysis Conditions

Abstract An one-pot synthesis of allylic nitriles 3 from the corresponding nitro derivatives 1 is described. In the first step the substrates 1 are reduced to the oximes 2 by carbon disulphide in the presence of wet potassium carbonate, in solid-liquid PTC conditions. In the second, the formed oximes 2 are dehydrated by adding more CS2 and 15% aqueous NaOH.

Regioselective opening of epoxyaldonolactones to fluorodeoxyaldonolactones using Tetrabutylammonium dihydrogentrifluoride

Abstract A study on the hydrofluorination of epoxyaldonolactones with Bu4N+H2F3− (1) under solid-liquid PTC and homogeneous conditions has been performed. Unsubstituted 5,6-epoxy-hexono-1,4-lactones 2a give the corresponding fluorohydrins in high yield using catalytic amounts of 1 and an excess of solid KHF2, while an equimolar amount of 1 is used with 2,3-epoxyaldonolactones 2d–g and 5,6-epoxy-hexono-1,4-lactones containing a free hydroxy group 2b,c. In all cases the reaction is completely regio- and stereoselective affording 6-deoxy-6-fluoro-hexonolactones 3a,b and 2-deoxy-2-fluoro-aldonolactones 3d,f.

A Convenient Synthesis of N-Alkyl and N, N-Dialkyltrifluoroacetamides in a Solid-liquid Two-Phase System in the Presence of Phase-Transfer Catalysts

Abstract Trifluoroacetamide is easily monoalkylated in a K2 CO3-organic solvent solid-liquid two-phase system affording in good to excellent yields N-alkyltrifluoroacetamides. Under the same conditions, the latter, in turn, react with alkylating agents giving N, N-dialkyltrifluoroacetamides in high yields.