## 3 Chemistry and Biological Activities of Selected Meroterpenoids
Then, compound **278** was converted to mananuthaquinone (**165**) via global acid deprotection and salcomine (a coordination complex of salen ligand and cobalt) mediated oxidation reaction sequence in moderate yields. In addition, compound **276** was subjected to deprotection and intramolecular cation trapping with the free phenol group to provide natural product aureol (**279**), which was subsequently converted to 5-_epi_-aureol (**166**) via epiperization of the decalin bridge carbon, using HI. Intermediate **166** is known to generate natural product cyclosmenospongine **164**[86]. The efficient synthesis provides rapid access to various family members and the established platform will enable the generation of derivatives for further biological studies. These unique spiromeroterpenoids share a common biosynthetic pathway that presumably arises from the terpenoid precursor famesyldiphosphate and display promising biological properties [87]. The total synthesis of asnovolins and related spiromeroterpenoids feature a key lithium mediated coupling reaction to establish the carbon-carbon bond formation that giving rise to the spirocenter, was recently reported by [PERSON] [87], shown in Scheme 22. The synthesis began with known chiral hydroxy enone **283**, which was converted to the corresponding neopentyl iodide via one-port triflation, followed by an \(\mathrm{S}_{\mathrm{N}}2\) reaction, which upon subsequent Luche reduction, provided ally alcohol **282**. Coupling reaction between the decalin system **281** and the lithium exchanged form of the iodide **282** via 1,2-addition reaction afforded compound **284**. Next, treatment of the resultant product **284** with \(\mathrm{MnO}_{2}\) was converted to spirocycle **280** via tandem allylic oxidation, followed by oxa-Michael addition reaction sequence. Spirocycle **280** was then transformed to spirocyclic intermediate **285** via a metal hydride atom transfer (MHAT) process mediated by Fe(acac)\({}_{3}\) in the presence of hydride source \(\mathrm{PbSiH}_{3}\), establishing the desired stereochemistry. Enolization of spirocyclic intermediate **285** with TMSOTf followed by treatment with Eschenmoser's salt, generated exocyclic enone **286**. Under various reactions conditions compound **286** resisted isomerization to the endocyclic enone **287**. Therefore, compound **285** was oxidized with 2-iodoxybenzoic acid (IBX) to the spirocyclic enone system, which was iodinated at the \(\alpha\)-carbon to provide the halogenated spirocyclic intermediate **288**. This system was then subjected to Suzuki coupling reaction to generate the desired endocyclic enone **287**, followed by final desaturation, and protecting group removal to generate the spiromeroterpenoid chermesin B (**172**). Compound **288** could be further functionalized via Pd mediated methylation to produce **287** again, which was treated with base to conduct an enolate acylation and deprotection to access the natural product asnovolin B (**168**). The natural product **168** was then subjected to Baeyer-Villiger oxidation in the presence of Sc(OTf)\({}_{3}\) to yield asnovolin A (**167**). The lactone ring opening of asnovolin A (**167**) was conducted using methanolysis conditions to provide natural product asnovolin E (**173**). In addition, compound **287** was acylated to generate compound **289**, which was desaturatedand deprotected to afford advanced spirocyclic intermediate **290**. Finally, compound **290** was subjected to Meerwein-Ponndorf-Verley reduction conditions to produce simplicissin (**171**) as the major product. The powerful linear synthesis enables access to many members of these natural products  
Asperterpene A and its related family are interesting structures with unique chemistry and biology. Asperterpene meroterpenoids displays an unprecedented 1,2,5-trimethyl-4,9-dioxobicyclo [3.3.1]non-2-ene-3-carboxylic acid moiety that is distinct from other similar meroterpenoids such as berkeleytrione and preastunoid A.