The question image/reaction scheme and the actual option structures are missing. Only the text

"The compound A in the following reaction is :"

is provided, but no reaction and no option details are visible. Therefore, the compound $A$ cannot be determined from the given information.

Step-by-step assessment

1. To identify compound $A$, we must know:

   • the starting compound,
   • the reagents/conditions,
   • the product or reaction sequence,
   • and/or the structures of options $A, B, C, D$.

2. In the current prompt, all of these are absent.

3. Hence, no chemical deduction is possible.

Conclusion

With the provided data, the answer cannot be derived reliably.

Since the stored correct answer is given as $D$, but there is no supporting reaction scheme or option structure to verify it, I cannot independently confirm that choice.