Triquinane derivatives

Just one reaction has been described where lithiated methoxyallene 42 reacted with bicyclo[3.2.0]heptenone 175 to form the triquinane derivative 176 via a tandem oxy-Cope-transannular ring closure sequence (Eq. 8.31) [111]. However, cycloocta-none 177 was isolated as a major product, which is unusual since other alkenyl-lithium compounds and 175 provide only triquinanes. The authors assumed that the additional sp2-hybridized C-atom in the eight-membered ring intermediate (eno-late of 177) induces a conformation which is less susceptible to transannular ring closure. 

Among the variety of terpenes which were synthesized with an intramolecular meta photocycloaddition as key step, triquinane derivatives were particularly well studied. Two isomers of these compounds are readily accessible via intramolecular meta cycloaddition in position 1,3 (Sch. 9). The following cyclopropanation reaction of intermediate O controls which of the angular or linear isomers is formed (Sch. 17) [67]. As this step is almost always unselective, both isomers are concomitantly formed. However, one of the isomers can be obtained predominantly via an additional photochemical equilibration step (compare Sch. 11). The triquinane frame is obtained by rupture of the distant C-C bond of the cyclopropane in connection to the 10-membered ring moiety. 

Acetophenone-sensitized irradiation of (83) affords an 80% yield of the triquinane derivative (84). This product is the key intermediate in a new synthesis of (— )-hirsutene. The tricyclotridecenones shown in Scheme 3 are photoreac-tive. Irradiation with acetone as the sensitizer brings about an oxa-di- jt-methane rearrangement to yield (85) while direct irradiation in benzene gives (86) by a... 

Acepentalene (C10H6) and Related Unsaturated Triquinane Derivatives... 

Chen and coworkers reported organocatalytic asymmetric [4 + 2] formal cycloadditions of cyclohexenylidene malononitriles with enals. This reaction afforded chiral bicyclo[2.2.2]octanes. Higher-order cycloadditions can also be catalysed by prolinol silyl ethers. Intramolecular [6 + 2] additions of fulvenes substituted at the exocyclic 6-position with a 5-formylalkyl group afforded synthetically useful linear triquinane derivatives in good yields and excellent enantioselectivities. ... 

Whereas the preceding processes involving ring openings of cyclopropanes provide useful [3+2] entries to cyclopentanes, the use of simpler substrates in [3+2] cycloadditions is made possible by the development of reductive cycloaddition pathways. Such reactions were initially developed in the context of stoichiometric processes, where metallacycles were prepared by oxidative cyclizations of enones and alkynes, followed by either protonation or alkylation of the nickel 0-enolate functionality. Catalytic protocols involving various intramolecular combinations of 7t-systems include formal [3+2] reductive cycloadditions of bis-enones to form bicyclooctanols (Scheme 3-33), of enones with unsaturated acyl oxazolidinones to form triquinane derivatives, and of enals with alkynes to form bicyclooctenols. ... 

Schafer demonstrated that ring closure of oxygen and nitrogen-containing precursors provided the corresponding tetrahydrofurans and pyrrolidines in moderate to good yields [21, 22]. The triquinane derivative 39 was also prepared in a similar way [23]. Marko et al. revealed that... 

INTRAMOLECULAR (2+2) CYCLO-ADDmONS OF KETENES AND VINYLKETENES TO OLEFINS. 3. THE SYNTHESIS OF ANGULAR ANNULATED TRIQUINANE DERIVATIVES. 

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