Some reactions of acyl cation equivalents with nucleophilic aromatic systems

Trimethyloxonium fluoroborate rapidly reacts with nitriles at elevated temperatures, to afford N-methylnitrilium salts. Subsequent reaction with π-excessive heterocyclic aromatic systems has been shown to give rise to iminium salts in moderate to excellent yields. The related imines may be obtained by deprotonation, and these compounds can be converted further by reduction or hydrolysis to secondary amines or ketones respectively. The reactions studied provide access to acylated indoles and pyrroles which are obtainable by other methods in inferior yields. The related reactions with carbocyclic aromatic systems were studied in an attempt to determine the range of heteroatom ring substituents which may be used