General Approach for the Synthesis of Polyquinenes via the Weiss Reaction. 14. Synthesis of Ellacene (1,10-Decanotriquinacene) and Studies of the Proposed Dimerization to a Substituted Dodecahedrane

Article abstract of DOI:10.1021/jo00045a023

Ellacene 4, a tetracyclic 1,10-centrosubstituted triquinacene, has been synthesized via the Weiss reaction.The condensation of cyclododecane-1,2-dione (5) with di-tert-butyl 3-ketoglutarate (6) under aqueous alkaline conditions provided 13,15,16,18-tetrakis(tert-butoxycarbonyl)tricyclo<10.3.3.0^1,12>octadecane-14,17-dione in the bisenol form 7 in 85 percent yield.The bisenol ether 8 was regioselectively monoalkylated to furnish in 96 percent yield the monoallyl ester 9 which was hydrolyzed to provide 13-allyltricyclo<10.3.3.0^1,12>octadecane-14,17-dione (10).Intramolecular aldol reaction of the related diketo aldehyde 11 to furnish 17-hydroxytetracyclo<11.5.2.0^2,13.0^2,16>eicosane-15,19-dione (12) was carried out under aqueous acidic conditions.The Lewis acid mediated (BH3/THF) reduction of the diketo alcohol provided the corresponding triol 13 in excellent yield.Conversion of the triol into the trisxanthate 21 followed by syn elimination (HMPA, 220 deg C) provided the desired triene 4 in 91 percent yield.Attempted dimerization of 4 (ellacene) to a substituted dodecahedrane 3 under photochemical conditions and/or high pressure (130 kbar) has failed to generate 3 to date under conditions that did effect <2+2> dimerization of the parent, triquinacene.