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Caffeine: spot the methylation-order flaw

Single question

Three N-methylations to convert xanthine into caffeine. The reagents are right and the named reaction is right; the order is wrong. Which methylation cannot run first under simple base + MeI?

N-methylation regioselectivity
NH acidity ordering on xanthine
Order-of-operations in heterocyclic chemistry

Find the flaw

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