o-Aminomethylderivatives of phenols. Part 3. Mechanistic investigation of a Mannich reaction of phenols with N-methylenealkylamines

The mechanism of the Mannich reaction of phenols (1) with 1,3,5-trialkyl-hexahydro-1,3,5triazines (2) as a source of N-methylenealkylamines (3) in organic solvent has been investigated. It has been determined that the formation of o-hydroxybenzylamine 4 and its subsequent quick transformation into benzoxazine 5 and primary amine in the reversible reaction with 3 takes place in the first stage of the process. Then, the yield of 4 slowly increases and that of 5 appropriately decreases as a result of the reaction of 3 with the so far unreacted 1 and the slow aminolysis of 5. In addition, benzyldiamine 6 is formed as a by-product (Scheme 1).