Cinchonidine: spot the stereochemistry flaw

Single question

Final step in a cinchonidine endgame: reduce cinchoninone to the C9 carbinol with NaBH4 plus a chiral additive. The reactant, reagents, and conditions match. Check the absolute configuration on C9.

Stereochemistry of cinchona alkaloids (C8/C9 assignment)

Cinchonidine vs C9-epi-cinchonidine

Enantioselectivity inversion of organocatalysts on epimerization

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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