The 2300X and 2500X are AMD's newest Ryzen 3 and Ryzen 5 CPUs, respectively. They boost to 4.0GHz support all-core overclocking. Therefore, they may be seen as promising for starter or modest builds. However, both processors have been announced as exclusive to OEMs and SIs.
https://www.notebookcheck.net/Ryzen-5-2500X-and-Ryzen-3-2300X-are-not-available-for-custom-builds.332240.0.html