Synthesis talk is not allowed when it deals with watched or dangerous chemicals or reactions, and when they are for commercial purposes. We allow talk of simple synthesis such as harmaline to THH, or reduction of DMT n-oxide to DMT, since they don`t fit that negative criteria.
Synthesis is the creation of a new molecule that wasn`t there in the first place, while extraction just separates the molecule(s) that has been already synthesized by the plant you are extracting from.
We also have guidelines for extraction talk, for example no talk of commercial extractions, unsafe settings and proceedures, etc.
It is all for obvious safety reasons.
You can check this in the attitude page:
https://wiki.dmt-nexus.me/Attitude_PageHope that helps