The question refers to "the reaction given below" and asks for the structure of starting compound $P$, but the actual reaction scheme/image is missing. Also, the options $A, B, C, D$ are blank in the provided text.

Because of that, the structure of $P$ cannot be determined from the information available.

Why the problem cannot be solved as given

1. To identify starting compound $P$, we need the reaction sequence/products/reagents.
2. For an MCQ, we must also inspect the given options.
3. Here, neither the reaction nor the option structures are present.

So, a chemistry-based derivation is not possible from the current data.

Conclusion

With the provided information, the answer cannot be independently verified.

Please share the reaction image/scheme and option structures so I can solve it step-by-step and compare properly with the stored answer.