Betweenanenes synthesis

As the first step in extending this novel and facile betweenanene synthesis to the [lO.lOjseries of compounds, they prepared the (Z)[10.10] precursor 73 from 1,2-cyclododecanedione (65), using McMurry s ring closure of the dialdehyde 72b as the key step. 

Marshall s original but rather involved [10.10]betweenanene synthesis has been improved in their second approach which reportedly presented a sixfold improvement in overall yield55d). 

The cyclic phosphate and phosphoramidate derivatives of v/c-diols undergo a two-step reductive elimination on treatment with Li/NHs, Na-naphthalene, TiCl4-Mg(Hg) or TiClt-K. In acyclic systems the reaction is only moderately stereoselective. The reaction has particular value in the synthesis of tetra-substituted alkenes from highly hindered v/c-diols. Scheme 20 illustrates its use in the synthesis of [10,10]-betweenanene (49). ... 

The synthesis of [10.10]-betweenanene (55) at Northwestern University was rather involved, so only part of it is reproduced in Figure 13. The starting material is 1,2-cyclododecanedione (50), which was converted into a 1 1.5 mixture of cis-trans isomers of the diepoxides (51). After separation from the cis isomer, the trans isomer was transformed into the diester 54 via 52 and 53 through eight steps. Acyloin condensation of 54 followed by modification of the remaining functional groups completed the synthesis of 55, m.p. 64-65°C. 

In his recent review of betweenanenes, Marshall (74) reported the synthesis of the [22.10] -compound, which was found to be inert toward complex formation with tetracyanoethylene, and toward hydroboration with isopinocampheyl-borane, suggesting that the [22] -bridge is not long enough to let the [10] -bridge pass through it. 

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