How Farnesol being synthesized?

It all started with an acetyl-CoA unit.

1. An acetyl-CoA unit condensed with one acetyl CoA unit producing acetoacetyl-CoA, which similar in Fatty Acid formation.

2. Acetoacteyl-CoA is once again condensed with one unit of acetyl-CoA to form β-hydroxy-β-methylglutaryl-CoA.

3. β-hydroxy-β-methylglutaryl-CoA undergo reduction (reduction of carbonyl into alcohol.

4. The alcohol undergoes further reduction forming Mevalonic acid.

 5. Mevalonic acid is phosphorilazed (add P) with decarboxylation (dehydration) to form IPP (isopentyl pyrophosphate), the biogenetic isoprene unit.

6. Isomerisation of IPP lead to DMAPP (active prenylating agent)

7. The reaction of DMAPP with other IPP (act as nucleophile) produce Geranyl pyrophosphate.

8. Geranyl pyrophosphate undergo hydrolysis to form Geraniol and its isomer Nerol.

9. Geranyl pyrophosphate can act with other IPP to form farnesyl pyrophosphate.

10. Farnesyl pyrophosphate can be further hydrolyzed to form Farnesol and its isomer (15 carbon compounds).   

11. Cyclization and rearrangement of farnesol lead to formation of other sesquiterpenoid compound (depending on whether cis or trans).