Dodecahedrane precursor

Intramolecular alkylation, acylation, and carbonyl addition by cr-sulphonyl carbanions, followed by reductive removal of the sulphur function, has also received considerable attention as a means of generating medium-sized rings, such as ( )-recifeiolide (61) (note the use of a r-allylpalladium complex as the electrophile see Scheme 6), cycloundecanone (82) (Scheme 7), and neocembrene. Other polycyclic systems, such as ( )-zizaene, potential dodecahedrane precursors, ... 

Another example of the acid-catalysed intramolecular cyclization of diazoketones cf. refs. 58, 92, 93) is a high-yielding preparation of polycyclic enones (101) from diazoketones (100). Further reports have appeared on the preparation of fused cyclopentanones by condensations between acetonedicar-boxylate and a-diketones yields are higher if the substituents on the latter substrates are small. An alternative approach to polycyclopentanoids, consisting of successive additions of propargyl alcohol anions to cyclopentanones followed by double dehydrative cyclization and hydrogenation, has been used to prepare the potential dodecahedrane precursor (102) cf ref. 63). The cage compound (103), obtained from 1,4-naphthoquinones and cyclopentadiene, produces the polycyclopentanoid (104) under acyloin condensation conditions. ... 

When the olefinic precursor to 866 was treated briefly with trifluoromethanesulfonic acid in dichloromethane solution, cyclization occurs with installation of the final dodecahedrane framework bond. The predominant product proved to be 557 in which methyl group migration has also taken pla( °l The symmetry of this first dodecahedrane was apparent from its spectral properties and nicely detailed... 

Significant efforts were carried out to obtain dodecahedrane via the similar carbocationic isomerization of appropriate polycyclic precursors.47,48... 

Triquinacene 10 which is now reasonably well accessible by a six to seven step synthesis [1,2], has long been envisaged as the logical precursor to acepentalene 3 [43] (see Scheme lb). Woodward et al. developed the first synthesis for triquinacene 10 [43] and suggested that it should be a potential precursor to both the fully unsaturated tricycle acepentalene 3 and dodecahedrane 88 [ 1,44]. Although many attempts have been made to cyclodimerize triquinacene 10,... 

The diester 87 with the same tetracyclic skeleton as 83 had previously been prepared by Paquette et al. via a domino Diels-Alder reaction of 5,5 -bicyclo-pentadienyl 84 with dimethyl acetylenedicarboxylate (Scheme 20) [73]. The key precursor 84 was obtained by iodine-induced oxidative coupling of the copper cyclopentadienide derived from the sodium derivative. The diester 85 formed along with 86 was transformed into a bissilyl bisenol ether by reductive cleavage of the central bond in the succinate moiety with sodium in the presence of trimethylsilyl chloride. Subsequent hydrolysis of the bisenol ether - actually a bisketene acetal - gave the dienic tetraquinacenedicarboxylate 87. This compound served as the key intermediate in the first synthesis of dodecahedrane 88 [74]. 

Also the fully unsaturated C20-fullerene 7 has been approached by Prinzbach et al. [44, 97]. As suitable precursors the perchlorinated dodecahedradiene C20C116 145 and the perbrominated dodecahedrane C20Br20 146 were prepared from 88 under forcing conditions. Due to their low solubility these compounds have so far only been identified by their infrared and mass spectra. Dehaloge-nation by fragmentation in the mass spectrometer has generated several unsaturated species but the occurrence of C20-fullerene 7 remains to be rigorously proved. 

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