Propellane triquinanes

Figure 1. Representative linear, angular, and propellane triquinane natural products.

Iterative trapping of the alkylpalladium species with tethered olefins is also possible, which allows tandem cycloisomerizations and zipper reactions to take place. Thus, depending upon the juxtaposition of the unsaturated bonds, Trost achieved highly atom-economical syntheses of triquinanes, propellanes (264) from the ynediene 263, and polyspiranes (Scheme 67).261... 

With this new notation, we can now consider briefly the retrosynthetic analysis of some triquinanes and propellanes discussed by Curran [29]. 

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... 

C,sH24, Mr 204.36, oil, bp. 65-70°C (33.3 Pa), [aJo -15.8° (CHCI3). A natural triquinane hydrocarbon with a [3.3.3]propellane structure from Isocoma wrightii (Asteraceae), an indigenous species of south west USA toxic to cattle and sheep, from South African Berkheya species, and the roots of Senecio isatideusK Derivatives of M. show antiproliferative activity. ... 

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