Cladiellin

The most general method for the synthesis of tetrahydrofurans based upon the IMSC methodology was developed by Overman et al. [53, 54, 94—96] For example, condensation of alcohol 221 with an aldehyde or a ketone in the presence of a Lewis acid leads to the formation of the carbocations 222a,b. The tertiary carboca-tion 222a undergoes a pinacol rearrangement and forms the desired heterocycle 224 (Scheme 13.82). Overman et al. used this approach during the synthesis of the various cladiellin diterpenes, which possess the core skeleton 224 [53]. 

The photo-rearrangement of cyclopentanones to tetrahydrofurans has been applied in the synthesis of the cladiellin skeleton (Equation 105) <2006JOC1172>. 

Tobacco has been the source of a number of macrocyclic diterpenoids. The 4-epimeric thunbergadiene-4,12-diols (105) are two further members of the series. The structure of one of the epimers was determined by X-ray analysis. Further examples of nor-isoprenoids which are possible degradation products of the macrocyclic tobacco diterpenoids have been described.Two further diterpenoids, cladiellin (106) and acetoxycladiellin (107), which are related to euni-cellin, have been obtained from a soft coral Cladiella species. The structure of the latter was derived by X-ray analysis. 

Eunicellanes and (infrequently) asbestinanes are diterpenes of marine origin, including eunicelline from the alga Eunicella stricta and cladielline found in some Cladiella species. Asbestinanes such as (-)-asbestinine 2 are characteristic of the gorgonia Briareum asbestinum (Araceae). 

Scheme 16.33 Total synthesis of cladiellins by the Clark group utilizing nn (F -selective r2.31-shift.

Kashman, Y. A New Diterpenoid Related to Eunicellin and Cladiellin from a Muricella sp. Tetrahedron Lett. 21, 879 (1980). 

Hochlowski, J.E., and D.J. Faulkner A Diterpene Related to Cladiellin from a Pacific Soft Coral. Tetrahedron Lett. 21, 4055 (1980). 

The C2-C11 cyclized cembranoids were isolated as secondary metabolites of gorgonian octocoral, which included the eunicellins (cladiellines), briarelUns, asbestinins, and... 

Distinct classes of compoiuids have also been successfully identified from corals (Table 2), as the characterization of the antifeedant hemiketal sterol 23-keto-cladiellin A (Fig. 7) from the exotic octocoral C. braziliensis (Southwest Brazil), which presented mtdn bands at 1716 v(C=0), 1663 v(C=C), 1606 vi(C=0)/vi(C=C), and 1452 (5(C—H), also identified in... 

Corminboeuf, O., Overman, L.E., and Pennington, L.D. (2009) A unified strategy for enantioselective total synthesis of cladiellin and briarellin diterpenes Total synthesis of briarellins E and F and the putative stmcture of alcyonin and revision of its stmcture assignment. J. Org. Chem., 74, 5458-5470. 

Hochlowski, J.E. and Faulkner, D.J. (1980) A diterpene related to cladiellin from a Pacific soft coral. Tetrahedron Lett., 21, 4055-4056. 

Molander, G.A., Czako, B., and St Jean, D.J.Jr. (2006) A general route toward the synthesis of the cladiellin skeleton utilizing a Sml2-mediated cyclization./. Org. Chem., 71,1172-1180. 

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