Reductive Carbon-Carbon Cleavage in Caged Systems. A New General Synthesis of Linearly Fused cis-syn-cis-Triquinanes

Article abstract of DOI:10.1021/jo00350a021

A concise and flexible approach to cis-syn-cis-tricyclo<6.3.0.0 2,6 >undecane-4,10-dione derivatives bearing the fused tricyclopentanoid framework has been established.The key concept in this synthetic theme is sequential, reductive carbon-carbon bond cleavage in readily and abundantly available pentacyclo<5.4.0.0 2,6 .0 3,10 .0 5,9 >undecane-8,11-dione (Cookson's dione 7).Reaction of 7 with zinc dust in acetic acid under sonic irradiation resulted in the formation of tetracyclic dione 8 in excellent yield through C 1 -C 7 bond reduction.The second C-C bondreduction (C 9 -C 10 in pentacyclic dione 7) was achieved by treating the tetracyclic dione 8 with an excess of Na-K alloy in the presence of trimethylchlorosilane to give cis-syn-cis-tricyclo<6.3.0.0 2,6 >undecane-4,10-dione (6).Several interesting transformations of the readily available cis-syn-cis-triquinane dione 6 are described.In an analogous manner, methyl-substituted derivatives 21 and 22 of the Cookson's caged dione are transformed to tricyclopentanoids 24 and 26, respectively, in moderate yields.The three hexacyclic diones 29,34, and 35 sharing common structural features with 7 also undergo sequential C-C bond reductions to furnish novel polyquinanes 31,36, and 37, respectively.These examples support the generality and preparative utility of the approach delineated here.