Triquinane sesquiterpenes synthesis

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. 

The synthesis of other angularly fused triquinanes as well as linearly fused sesquiterpenes such as hirsutene and capnellene quickly followed. Many general methods for the synthesis of cyclopentanoid natural products emerged as a result of the target-oriented effort [6]. These accomplishments have been reviewed extensively on numerous occasions [7]. This chapter reviews the history of retigeranic acid from its isolation and structure determination to published approaches to its synthesis and the four total syntheses accomplished to date. 

The cyclization provides a route to the angularly fused triquinane system of 3, which lacks two of the methyl groups present in the natural sesquiterpene isocomene (4). Cyclization of a suitably substituted enyne for synthesis of 4, however, proceeds in minute yield.3... 

Magnus was the first to develop extensive synthetic applications of the Pauson-Khand preparation of the bicyclo[3.3.0]oct-l-en-3-one system. His efforts amply demonstrate the degree to which the high level of functionality in the Pauson-Khand products can be directly utilized in building more complex structures. A formal synthesis of the antitumor sesquiterpene coriolin illustrates a very efficient sequence for construction of the third ring in the linearly fused triquinane series in the presence of considerable functionality (Schemes 10 and 18). A synthesis of the related triquinane hirsutic acid utilizes the observation that the proper stereochemical relationship between the substituents at C-7 and the ring-fusion carbon (C-5) of the bicyclo[3.3.0]oct-l-en-3-one system, while not controllable in the cycloaddition reaction itself, may be readily established by acid- or base-catalyzed equilibration (equation 54 and Scheme 19). ... 

Balme, G. and Bouyssi, D. (1991) Total synthesis of the triquinane marine sesquiterpene ( )A 02) capneUene using apaUadium-catalyzed bis-cyclization step. Tetrahedron, 50,403-14. 

A palladium-catalyzed cyclization sequence involving a mal-onate anion-based termination step and leading to linear triquinanes has been reported and employed in the synthesis of the sesquiterpene-type natural product ( )-A ( -capnellene (eq 114). i ... 

Paquette, L.A. and Stevens, K.E. (1984) Stereocontrolled total synthesis of the triquinane marine sesquiterpene A -capnellene. Can. J. Chem., 62, 2415-2420. 

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