Sesquiterpenes triquinane

An intramolecular nitrile oxide cycloaddition also served as the key step in the stereoselective assemblage of the skeleton of angular triquinane sesquiterpenes of the isocomene series. Tetracyclic isoxazoline 203 was obtained from oxime 202 [derived from tetrahydroindandione 201] and on treatment with sodium hypochlorite... 

Intramolecular tandem Michael reaction.1 Angular triquinane sesquiterpenes such as pentalenene (5) have been synthesized from the bis(enone) 1 by an ntramolecular tandem Michael reaction as the key step for conversion to the rncvclic system. Lithium amides, even bulky ones, are not useful for this step, nor > dimethyl-t-butylsilyl triflate. Annelation can be achieved by reaction of 1 with c lSi(CH3)3, zinc chloride, and N(C2H5), at 160° in either toluene or CH2C12. Use... 

The photochemical transformations of vinylcyclopropanes are of mechanistic interest, but because of the high energy of the reaction intermediates, especially in the triplet manifold, practical applications are scarce. The regio- and stereo-selective aspects are, however, similar to those of the thermal processes. Additional methods that provide for the cyclopentene rearrangement involve the degenerate photochemical rearrangements observed by Wender during meta-photocycloaddition of arenes and alkenes and utilized extensively in the synthesis of triquinane sesquiterpenes. -" -" (See Section 8.1.9 or ref. 41 for a recent summary.)... 

Pauson-Khand reaction. In the presence of tetramethylthiourea the Pauson-Khand reaction suceeds with enynes in which the double bond is present in a silylcyclopropene unit. It enables a synthesis of the angular triquinane sesquiterpene (-)-pentalenene. ... 

A neat four-step synthesis of the triquinane sesquiterpene hirsutene (4) has been described, which features the novel iodotrimethylsilane induced rearrangement of the dione (1), to (2), as a key step. Reductive methylation of the enone (2) to (3),followed by Wittig methylenation then completed the synthesis. ... 

Although a number of syntheses of the angular triquinane sesquiterpene isocomene (18) have now been published, the synthesis by Dreiding et al. is interesting since it features the sequential alkynone cyclisations (14)— -(15) and (16)——(17) as the two key 5-ring annulation reactions. In a new synthesis of the related sesquiterpene silphinene (23) intramolecular(2+2] photocycloaddition from (19) is first used to elaborate the tricycle (20), which on brief exposure to iodotrimethylsilane produces (21). Reduction of (21) to (22), and functional group elaboration then completed the... 

Shibasaki has also reported impressive applications of the asymmetric intramolecular Heck reaction. For example, the Shibasaki group have applied their chemistry to the synthesis of compound 64, a key intermediate in the total synthesis of two complex triquinane sesquiterpenes 65 and 66, by making use of a Heck reaction/anion capture cascade sequence. ... 

Iwata, C., Takemoto, Y, Doi, M., and Imanishi, T. (1988) Stereoselective total synthesis of ( )- subergorgic add, a new type of angular triquinane sesquiterpene. /. Org. Chem., 53,1623-1628. Wender, P.A. and DeLong, M.A. (1990) Synthetic studies on arene-olefin cycloadditions. XII. Total synthesis of ( )-subergorgic acid. Tetrahedron Lett., 31, 5429-5432. 

Uyehara, X, Murayama, X, Sakai, K., Onda, K., Ueno, M., and Sato, X., Rearrangement approaches to cyclic skeletons. XIII. Total synthesis of triquinane sesquiterpenes, ( )-modhephene and ( )-isocomene, on the basis of formal substitution at both bridgeheads of a bicyclo[2.2.2]oct-5-en-2-one. Bull. Chem. Soc. Jpn., 71, 231, 1998. 

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