Triquinans, synthesis

N. Naz, T. H. Al-Tel, Y. Al-Abed, and W. Voelter, Synthesis of polyfunctionalized bis-annulated pyranosides Useful intermediates for triquinane synthesis, Tetrahedron Lett. 35 8581 (1994). 

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... 

Hudlicky developed a general method of triquinane synthesis based on a cyclopropanation- arrange-ment sequence of dienic diazo ketones (Scheme 52). Topological selectivity of linear versus angular triquinane synthesis has been achieved. ... 

A linear triquinane synthesis is started from a bicyclo[6.3.0]precursor initiated by chemoselee-tive Lewis acid attack on the least hindered olefin. Reaction of precapnelladiene (10) to capnellene (11) can be carried out in refluxing benzene in the presence of boron trifluoride-diethyl ether complex22 giving a yield of greater than 50%. 

Scheme 44. Triquinane synthesis involving the generation of an alkyl radical from an alkenyl radical via 1,5-hydrogen transfer...

Another interesting protocol for triquinane synthesis is illustrated here. Thermal reaction of epoxy-A-aziridinyl imines in refluxing toluene initially generates the reactive alkylidene carbine, which undergoes intramolecular insertion reaction and a radical cascade to afford the tricyclic alcohol (Scheme 6.38). The triquinane thus formed can be easily converted to hirsutene as depicted [42]. 

Rearrangements. AICI3 catalyzed rearrangement of hydrocarbon derivatives to adamantanes has been well documented (eq 35). Other rearrangements have been used in triquinane synthesis (eq 36). ... 

Singh, V. and Thomas, B., Aromatics to triquinanes synthesis and photoreaction of tricy-clo[5.2.2.0 > ] undecanes having an a-methoxy-P,y-unsaturated carbonyl chromophore a novel ef cient and general route to linearly fused cisiantixis tricyclopentanoids, /. Org. Chem., 62,5310, 1997. 

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