Triquinanes linear

It should be noted that this strategy could also be utilized to build up the linear triquinane framework 3-257 in 45% yield, employing the 11-membered ring system 3-256 in which the BMDMS group is simply moved from one to the other side of alkyne moiety as compared to 3-252 (Scheme 3.66) [105],... 

Although Wender s synthesis was completed prior to Hudlicky s, it was published later [65]. It utilized the technique of mefa-photocycloaddition of arenes that Wender developed into a general method of synthesis for both angular and linear triquinanes. The overall strategy was centered around an intramolecular Diels-Alder cycloaddition for construction of the internal six-membered ring of the target. 

Linear triquinanes.3 Reaction of the trienyl bromide 2 with 1 (AIBN, 80°) results in at least eight products. The two major ones (27% yield) are the epimeric triquinanes 3 and 4. 

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... 

A chemoenzymatic synthesis of the linear triquinane (-)-hirsutene and identification of possible precursors to the naturally occurring (+ (-enantiomer. Tetrahedron, 60 (3), 535-547 (b) Banwell, M.G., Edwards, A.J., Harfoot, G.J., and Jolliffe, K.A. (2002) A chemoenzymatic synthesis of (—)-hirsutene from toluene. Journal of the Chemical Society, Perkin Transactions 1, 2439-2441. 

An elegant application of this photocycloaddition in the field of triquinane synthesis has been reported by Reddy and Rawal [160]. The initially formed oxetane 163, formed from the Diels-Alder adduct 162, is easily cleaved reductively (by use of LiDBB = lithium di-/er -butyl-biphenylide) to give 164. This approach was also used for the construction of structurally diverse di- and (propellane-type as well as linear or angular anellated) triquinanes [161]. The classic linear triquinane hirsutene is also available via this route [162]. Star-like molecules like the tiene 167 are available via a sequence of intramolecular photocycloaddition (from the 1,3-cyclohexadiene/acylallene adduct 165) and oxetane (166) ring-opening (Sch. 58) [163]. Further examples of intramolecular... 

H-silphiperfol-5-ene 93 (R = 11, R2 = Me) [70], subergorgic acid 94 [71], crinipellin B 95 (formal synthesis) [72], (—)-retigeranic acid 96 (formal asymmetric synthesis) [73] were synthesized via intramolecular meta cycloaddition as key step (Sch. 18). In the same way, linear triquinane... 

Reductive cyclization.1 Reduction of the unsaturated aldehyde 1 with Sml2 in THF/HMPT (20 1) at 0° effects a tandem radical cyclization of the fram-3,5-disubstituted cyclopentene system to a linear triquinane unit (2) with surprisingly high cw-ann-di-stereoselectivity. 

Very likely the ammonium fluorides are the proton sources and therefore the reason for incomplete conversions, since potassium fluoride in acetonitrile gives high yields in a very elegant [3 + 2]-annuIation process 87). It combines a Michael addition to a vinyl phosphonium salt with an intramolecular Wittig reaction and proceeds only in the presence of 18-crown-6 with satisfying yield. This cyclopentene synthesis has been executed in a repetitive manner to prepare linear triquinanes as illustrated in Scheme 6. Unfortunately, the sequence is non-stereoselective with regard to the ethoxycarbonyl functions. 

V. K. Singh and B. Thomas, Recent developments in general methodologies for the synthesis of linear triquinanes, Tetrahedron 1998, 54, 3647-3692. 

Transmetalation of the allyllithium intermediates allowed access to the cuprate manifold of reactivity. The rapid construction of a linear triquinane, 229, using this methodology demonstrates the potential for synthetic application (Scheme 70). 

The pentalenene precursor (141) can be derived firom a TMM cycloadduct (142) (equation 147). This synthetic approach is expedited by the facile conversion of the methylene unit of (142) to a gem-di-methyl function found in (141). This is normally accomplished by a simple cyclopropanation-hydro-genolysis sequence. The two reported TMM-based syntheses of the linear triquinane (l)-hirsutene (143) also utilize this particular strategy for the gem-dimethyl formation (equation 148). ""... 

Isomerizations. A synthetically useful transformation is the rearrangement of linear triquinanes to the angular isomers. For the conversion of propargyl ethers to allenyl ethers microwave promotion is advantageous. ... 

Oxidation of 4-methoxycarbonyl-2-methoxyphenol (421) with PhI(OAc)2 in MeOH was carried out in the presence of cyclopentadiene (CPD) to afford in 87% yield a Diels-Alder adduct 434, which was subjected to photochemical reaction followed by Ac20-BF3-Et20 treatment to give a linear triquinane 435 (47.6% in 2 steps). ... 

Singh, V., Alam, S. Q., Intramolecular Diels Alder Reaction in 1 Oxaspiro[2.5]octa 5,7 dien 4 one and Sigmatropic Shifts in Excited States Novel Route to Sterpuranes and Linear Triquinanes Formal Total Synthesis of ( ) Coriolin, Chem. Commun. 1999, 2519 2520. 

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