General Approach to the Synthesis of Polyquinenes via the Weiss Reaction. 6. Progress toward the Synthesis of Dicyclopentapentalenes

Article abstract of DOI:10.1021/jo00245a037

The synthesis of the three tetraquinanes tetracyclo<7.2.1.0^4,11.0^6,10>dodecanetetraol (27), tetracyclo<6.6.0.0^2,6.0^9,13>tetradecanediol (36), and tetracyclo<6.6.0.0^2,6.0^10,14>tetradecanediol (39) has been achieved via the Weiss reaction.Reaction of glyoxal (4a) with di-tert-butyl 3-oxoglutarate (5b) gave tetra-tert-butyl 3,7-dioxo-cis-bicyclo<3.3.0>octane-2,4,6,8-tetracarboxylate (6b) in excellent yield.This was converted, regiospecifically, into bisenol ether 20b with diazomethane.The bisalkyllation of 20b was effected with allyl iodide/KH to provide a mixture of the 2,6-diallyl regioisomer 23b (64percent) and the corresponding 2,8-diallyl dione 24b (36percent); the former compoud crystallized from the reaction mixture.Hydrolysis of teraester 23b furnished 2,6-diallyl dione 7, which was oxidized and cyclized to diketo diol 26, isolated as a mixture of diexo and diendo stereoisomers 26a and 26b, both of which were reduced with borane-tetrahydrofuran to provide the desired tetraol 27 in 80percent yield.The HMPA-mediated dehydration of 27 gave the tetracyclotetradecadiene 28.Furthermore, the 2,6-diallyl diones 7a and 7b were converted with HBr-peroxides into dibromides 35a,b, and this mixture of epimers was cyclized to the tetracyclotetradecanediol 36 on stirring with samarium diiodide (80percent yield).Analogous to the chemistry developed for preparation of 36, the 2,8-diallyl tetra-tert-butyl ester 24b was converted into the 2,8-bis(3-bromopropyl) dione 38, which cyclized on treatment with SmI2 to the desired tetracyclic tetradecanediol 39 in 69percent yield.