Total synthesis of terpenes. XV. Synthesis of 3,10-dimethoxy-6a.beta.,12b.beta.-dimethyl-5,6,6a,6b.alpha.,7,8,12b,13-octahydropicene, a potential intermediate in triterpene synthesis

Stereoselective total synthesis of (.+-.)-trichodiene: biogenetic precursor of the trichothecane sesquiterpenoids

“…These enones were separated by high-pressure LC on 15% silver nitrate impregnated silica gel 6031 with 2.5% ether-97.5 % petroleum ether (bp °C) as an eluant. Trichoenone (18) was converted into (i)-trichodiene (1) in 51% yield with 10 equiv of methylenetriphenylphosphorane Wittig reagent32 in scrupulously dried dimethyl sulfoxide, despite the fact that previous reports1,131,25 indicated that this reaction was unsuccessful. The IR, NMR (60 and 100 MHz), and mass spectral data for synthetic (±)-trichodiene (1) and the corresponding monoas well as the diepoxide11 of 1 were identical with the respective data reported1"3,11 for the natural substance.…”

“…Dieckmann condensation of diester 25 with 3 equiv of sodium bis(trimethylsilyl)amide29 in DME followed by quenching with 10% hydrochloric acid solution at 0 °C and chromatography on silica gel 60 with a solution of 10% ether-90 % petroleum ether (bp 30-60 °C) as an eluant gives ß-keto esters 26 and 27 in 78% overall yield as a 63:37 ratio of trito disubstituted alkene isomers. Decarboxylation of d-keto ester 26 to bazzanenone 28 is smoothly accomplished in 95% yield by treatment of 26 with DBU30 in 2,4,6-collidine at 180 ± 5 °C for 3 h. A Wittig reaction32 on synthetic bazzanenone (28) under identical conditions with those utilized for (db)-trichoenone (18) showed only about 5% conversion to a product containing an exocyclic methylene moiety as indicated by NMR spectra of the crude reaction material. This result could not be improved even after repeated attempts to do so.…”

“…Oxidation of enol 23 with Jones reagent17 in acetone followed by chromatography of the resulting mixture of enones on 15% silver nitrate impregnated silica gel 6031 with 25% ether-75 % petroleum ether (bp 30-60 °C) as an eluant gives enones 18 and 24 in 82% yield in a 81:9 ratio, respectively. Synthetic trichoenone (18) was then converted into (±Jtrichodiene (1) by the Wittig reaction32 described above.…”

Total Synthesis of Celastrol, Development of a Platform to Access Celastroid Natural Products

“…The absence of a synthesis can, in part, be attributed to the incompatibility of biologically inspired polyene cyclization strategies for the assembly of the celastroids or, for that matter, any members of the friedelin-type of triterpenes. These reactions are highly desirable as they provide rapid access to relatively large molecules with multiple stereogenic centers in a single transformation from linear, polyunsaturated precursors. , Unfortunately, however, the biological polyene cyclization leading to celastrol is exceedingly difficult to reproduce in the laboratory due to a set of complex and energetically unfavorable methyl and hydride shifts. − The closest natural products to celastrol to be synthesized were the pentacyclic triterpenes, alnusenone, and friedelin, both of which were prepared by Ireland. − Attempts to implement polyene cyclizations for these natural products failed to improve access to the natural products, however, were inspirational for our studies. , …”

Synthetic studies towards ryanodine

“…Crude ~was then esterified (CH3I, K2C03 in acetone) (14) and the resulting methyl ester product 92 was purified by distillation (=70% yield from carvone). Hydrolysis of 92 (NaOH in CH30H~gave pure acetal carboxylic acid 91 which was finally converted (LiH in THF and CH2=CHLi) into optically active dienophile 71A ([a]578 = +0.6°), Diene !l was then heated with a slight excess of 71A in benzene.…”