Wikipedia
Acetoacetyl-CoA
Acetoacetyl CoA is the precursor of HMG-CoA in the mevalonate pathway, which is essential for cholesterol biosynthesis. It also takes a similar role in the ketone bodies synthesis ( ketogenesis) pathway of the liver. In the ketone bodies digestion pathway (in the tissue), it is no longer associated with having HMG-CoA as a product or as a reactant.
It is created from acetyl-CoA by thiolase, and it is acted upon by HMG-CoA synthase to form HMG-CoA. During the metabolism of leucine, this last reaction is reversed.