Recent Advances in the Use of Acylium Salts in Organic Synthesis. A Brief Review

Polar Acetalization and Transacetalization in the Gas Phase: The Eberlin Reaction

“…They are available in the form of acylium ion salts or are formed in situ mainly from carboxylic acid halides . Acylium ions participate as key ionic reaction intermediates in the classical Friedel−Crafts acylation reactions 137 and have been used in the syntheses of a variety of heterocyclic systems such as tris(3,4,5,6-tetrahydro-1,3,5-triazinium) and tris(1,3,5-oxadiazinium) salts. , In the dilute gas-phase environment of the mass spectrometer, a variety of long-lived solvent- and counterion-free acylium ions have been generated, isolated, and reacted, and a rich gas-phase chemistry has been observed for such gaseous ions. Eberlin reactions of acylium ions occur by routes that are similar to the condensed-phase acetalization and transacetalization reactions.…”

Cyclization reactions of acylium and thioacylium ions with isocyanates and isothiocyanates: Gas phase synthesis of 3,4-dihydro-2,4-dioxo-2H-1,3,5-oxadiazinium ions

“…Acylium ions are also important species in solution playing a fundamental role in the well-known and industrially relevant Friedel-Crafts acylation reaction [31]. They are also useful intermediates in the condensed-phase synthesis of many heterocycles via reactions with cyanamides, carbodiimides, alkenes, alkynes, and nitriles [32]. Solvated acylium ions were also found to react with alkyl isocyanates to yield unique double-addition cyclic products, namely, 3,4-dihydro-2,4-dioxo-2H-1,3,5-oxadiazinium salts in moderate yields [33].…”