Complicatic acid

Banwell MG, Austin KAB et al (2007) Chemoenzymatic total syntheses of the linear triquinane-type natural products (+)-hirsutic acid and (—)-complicatic acid from toluene. Tetrahedron 63 6388-6403... 

Arene cis-diols can undergo cycloaddition reactions, acting as both diene and dienophile to produce homoadducts (12). Heteroadducts have also been synthesized, for example recent work by Banwell and coworkers exploited the reaction of toluene cw-diol with cyclopentenone as the initial step in their synthesis of complicatic acid and related triquinanes (20). We found that upon prolonged standing at room temperature in concentrated form, the acetorddes 5a and 5b were slowly converted to the Diels-Alder adducts depicted in Figure 2. 

Sesquiterpenoids of the triquinane type produced by fungi. The key step in their biosynthesis is the cycliza-tion of humulene to hirsutene (C,5H24, Mr 204.36, oil) which is isolated from cultures of Coriolus con-sors (Basidiomycetes). Hirsutene has been synthesized by more than 20 different routes. Functionalized hir-sutanes such as complicatic acid, hirsutic acid, hyp-nophilin, pleurotellic acid, and the coriolins isolated from basirUomycete cultures all possess the absolute configuration shown for hirsutene. 

C15H20O4, Mr 264.32, prisms, mp. 182 °C, [a], +116° (CHClj). A sesquiterpenoid of the hirsutane type from cultures of the fungus Stereum hirsutum (basidiomycetes), frequently found on dead hardwood (see also complicatic acid). 

Polyquinanes. Polycyclic compounds with a skeleton of only 5-membered carbocyclic rings. Among natural products there are some tri- and tetraquinanes derived from the isoprenoid pathway. Different condensation types exist. Triquinanes are often condensed in a linear way, such as capnellene, complicatic acid, the coriolins, the hirsutanes, and phellodonic acid. Different triquinanes are isocomene, modhephene and pentalenene. The only known natural tetraquinanes are the crinipellins, isolated from mushrooms. 

Photoinduced epimerization reactions are sometimes encountered during the course of the ODPM rearrangement. Thus, it has been observed, as part of a study directed toward the total synthesis of (+)-hirsutic acid and (-)-complicatic acid, that triplet-sensitized irradiation of compound 97 affords the anticipated primary photolysis product 98, but this is accompanied by quantities of epimer 99. Sustained irradiation leads to increasing quantities of the thermodynamically favored isomer 99, presumably via either photoenolization of precursor 98 or through photoinduced C—C bond homolysis within the same compound followed by diradical recombination (to generate 99). 

Cg]Acetate gave a labelling pattern in 5-dihydrocoriolin C 4.96) which could be clearly interpreted in terms of a pathway based on the humulene skeleton 4.95) (Scheme 4.19). A similar route to related compounds, hirsutic and complicatic acids, and the illudins, is likely [91-94]. 

---