The question as provided is incomplete.

1. To identify compounds $A$ and $B$ in a reaction sequence, I need the actual reaction scheme or the listed options.
2. In the prompt, the reaction sequence is missing, and the options are shown only as:
   • $A:$
   • $B:$
   • $C:$
   • $D:$ with no chemical structures or names.
3. Therefore, it is not possible to derive $A$ and $B$ from the given information.

So, a step-by-step chemical solution cannot be completed unless you provide:

• the reaction sequence/image, and
• the actual option contents.

Since the stored correct answer is given as $C$, I cannot verify whether that is correct without the missing reaction data.