The question refers to a reaction scheme and options $A, B, C, D$, but in the provided prompt the reaction scheme itself is missing, and the structures of options A–D are also not visible.

So the problem, as currently provided, does not contain enough chemical information to actually determine the major product $Z$.

What is missing

To solve this, I would need:

1. The starting compound / substrate
2. Reagents and conditions in the reaction scheme
3. The structures corresponding to options $A, B, C, D$

Without these, no step-by-step organic mechanism can be carried out.

Conclusion

Because the reaction scheme and answer choices are absent, the major product cannot be derived from the given text alone.

However, the stored correct answer is given as A. Since I cannot independently verify it from the missing reaction information, I cannot honestly confirm agreement based on chemistry reasoning.