Cyclohexane-1,2,3-trione formation

The unexpected 8-hydroxymethylhexahydropyrido[2,3-, pyrimidine-6-spiro-l -cyclohexane-2, 4,6 -triones 520 were obtained from microwave-assisted cyclocondensation of equimolar amounts of 6-aminopyrimidin-4-ones 460 and dime-done with a large excess of formaldehyde (37% in water) in the presence of EtsN as a catalyst <2006TL27>. The reaction proceeded via an initial formation of the 2 1 dimedone/formaldehyde adduct 521 that gave intermediate 522 and 523 which could undergo cyclocondensation with excess formaldehyde to give 520 (Equation 42) <2006TL27>. 

Scheme 5. Formation of cyclohexane-1,2,3-trione l,3-bis(phenylhydrazone) by a free-radical mechanism.235-241...

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