Selective mono, bis, and trisiminoformylation of 2,4,6‐trialkyl‐1,3,5‐triazines ‐ unusual enol acylenamine tautomerism of hydroxyalkenyl‐1,3,5‐triazines

2,4,6‐Trialkyl‐1,3,5‐triazines 1 can selectively be mono, bis or trisiminoformylated by reaction with trismorpholinomethane 2 or chloromethylene iminium salts 3 (Vilsmeier reagents), with each alkyl substituent reacting with only one molecule of the electrophile. The resulting aminoalkenyltriazines 4, 5 and 6 are partially or fully hydrolysed to corresponding formylation products. The latter exist either in enol or in unusual acylenamine tautomeric structures 10, 12 , and 13 , depending on the number of enamine or enol units found in the molecule. Reaction of triazines 1 with chlorobenzylidene iminium salts 16 gives monoiminobenzoylation to enaminotriazines 17 .