One of the possible methods for treatment of neurodegenerative disorders such as Alzheimer’s and Parkin’s disease is to enhance the expression levels of neurotrophic factors, which can increase neuronal activity in neuronal cells. Thus, our goal is to find new agents to function as neurotrophic factors from the world of small molecule natural products (SMNP’s) and develop total synthesis to gain access to a large quantity of such compounds. Paecilomycine A, isolated from a metabolite of Paecilomyces tenuipes which is a well known fungus used in folk medicine in eastern Asian countries, is an effective lead compound to investigate neurotrophic activity because the in-vitro study indicates that it could indirectly induce neurite outgrowth in PC-12 cell as low as at a concentration of 10 nM. The first total synthesis of paecilomycine A has been achieved in a concise way. Key features include a stereoselective Diels-Alder cycloaddition and an intramolecular Pauson-Khand reaction. In addition, a procedure has been developed for the construction of 7,5-fused ring systems through the ring expansion of silyl enol ethers. This method has been applied to the synthesis of a hydroazulene structure of neurotrophic diterpene, tricholomalide A.