Trimethoprim: spot the fabricated intermediate

Single question

Three-step route to trimethoprim: Knoevenagel between 3,4,5-trimethoxybenzaldehyde and a cyano partner, condense with guanidine, then aromatize. Look hard at the structure of the intermediate after the Knoevenagel.

Knoevenagel condensation mechanism

2,4-Diaminopyrimidine ring formation from beta-enaminones

Distinguishing real vs invented intermediates

Find the flaw

Click the step that contains the flaw, or pick “No flaw” if you think every step is correct.

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