In the given reaction
The number of chiral carbon/s in product A is ___________.

Solution

Chemistry ma’am · 4 steps

The ester has no α-H, so the ketone's methyl enolate attacks it and closes a six-membered ring.

1. Find the enolate. The ester's α-carbon is the ring carbon carrying CH₃. It has no H, so ⁻OEt cannot form an enolate there. The base must take an α-H from the ketone, from either its CH₂ or its CH₃.
2. Pick the ring size. The enolate attacks the ester C=O and ⁻OEt leaves. This is an intramolecular Claisen condensation. Attack from the CH₂ would close a strained 4-membered ring. Attack from the CH₃ closes a 6-membered ring, so that is the path taken.
3. Product A. A is a cyclopentane fused to a cyclohexane-1,3-dione. Going round the new six-membered ring: the quaternary C with CH₃, C=O, CH₂, C=O, CH₂, and then the ring-fusion CH, which closes back to the quaternary C.

   Carbon in A	Four groups attached	Chiral?
   Ring-fusion C with CH₃	CH₃, C=O, cyclopentane CH₂, ring-fusion CH	Yes
   Ring-fusion CH	H, cyclohexane CH₂, cyclopentane CH₂, quaternary C	Yes
   CH₂ between the two C=O	two identical H	No
   Both C=O carbons	only three groups (sp²)	No
   Every other ring CH₂	two identical H	No

4. So. Only the two ring-fusion carbons are chiral, so product A has 2 chiral carbons.

The common slip: 1. Counting only the quaternary carbon with CH₃ gives 1. The ring-fusion CH is also chiral, because its two ring CH₂ neighbours belong to different rings.

The idea to keep. In a Claisen or Dieckmann question, first check which carbonyl actually has an α-H, then pick the attack that gives a 5- or 6-membered ring. In fused rings, the ring-fusion carbons are the usual chiral centres.

Answer from the NTA final answer key. Solution by PrepWiser.