Geo-Scientist Prelims 2025 Chemistry Q103: The precursor [X] in the following reaction is :

The precursor [X] in the following reaction is :

1. (a) Malonate-tethered tricyclic enone with the side chain on the quaternary ring carbon (one C=C, conjugated to the ring ketone)
2. (b) Linear dienone O=C–CH=CH–C(R)=C< with the CH(CO₂Me)₂(CH₂)₃ chain on the γ-carbon of the dienone
3. (c) Dienone with the CH(CO₂Me)₂(CH₂)₃ chain on the β-carbon (C=C–C=C ring, chain meta to C=O)
4. (d) Dienone with the CH(CO₂Me)₂(CH₂)₃ chain on the α-carbon next to the ring C=O