Acylation of tertiary amides. Formation of 1-acyloxyiminium salts and 1-acyloxyenamines

Tertiary carboxamides are acylated at the oxygen atom by benzoyl or acetyl chloride in the presence of silver trifluoromethanesulphonate; if the resulting 1-acyloxyiminium salts contain hydrogen atoms at positions 2 or 4 they can be deprotonated to yield unstable 1-acyloxy-enamines or -dienamines, which have been trapped by reaction with 4-phenyl-1,2,4-triazoline-3,5-dione.