1-Alkyl-1,2,4-triazinium Ylides as 1,3-Dipoles in a Cycloaddition Reaction with Diethyl Acetylenedicarboxylate

Deprotonation of 1-alkyl-5-phenyl-1,2,4-triazinium salts by triethylamine results in the formation of azomethyne ylides which undergo a 1,3-dipolar cycloaddition reaction with diethyl acetylenedicarboxylate to yield pyrrolo[2,1-f]1,2,4-triazines.