[details=“English Translation”]Although I explained, he wasn’t paying attention to listen to me.
[/details]
Does plain “le expliqué” sound right to you? I would prefer “se lo expliqué”. 
Additionally, the RAE has a different definition of the idiom:
estar en el caso
loc. verb. coloq. Estar bien enterado de un asunto.
The sentence sounds a bit off. I would also add “se” and change the “caso” idiom. Also, “escucharme” seems redundant to me. So:
- Aunque se lo expliqué, no estaba al caso (de escucharme).
And with other similar idioms:
- …, no estaba al tanto
- …, no estaba por la faena
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In the same collection, we also have “No creo que esté por la labor de ayudarnos con el proyecto.”
(I don’t think he’s willing to help us with the project.)
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