I. Mechanistic and synthetic studies on the scope of the Weiss reaction. II. Studies directed toward the preparation of staurane-1,3,5,7,9,11-hexaene on the route towards tetracoordinate planar carbon.

摘要

The mechanism of the Weiss reaction was studied with respect to the intermediacy of 4-hydroxycyclopent-2-ene-1-ones (1:1 adducts) in this process. Furil 128 was reacted with two equivalents of dimethyl 3-oxoglutarate 23 to afforded the cis-bicyclo (3.3.0) octane-3,7-dione 130 in 60% yield. When furil was reacted with one equivalent of 23, a new product was isolated which was fully characterized as the 1:1 adduct 132. When the 1:1 adduct 132 was reacted with one equivalent of 23, the 1:2 adduct 130 was isolated as the sole product. Similar results were obtained for the reaction of phenanthrenequinone 47 with 23. These experiments provide the first clear evidence that 4-hydroxycyclopenteneones are indeed key intermediates in the Weiss reaction. It is clear from the reaction of 23 with benzil 45, pyridyl 125, thenil 133, furil 128, and phanthrenequinone 47, coupled with ;Attempts to prepare tetrasubstituted cis-bicyclo (3.3.0) octane-3,7-diones through the alkylation of the bis enolether of tetramethyl 1,5-dimethyl cis-bicyclo (3.3.0) octane-3,7-dione 155 were impeded by difficulties in the hydrolysis of the hindered esters. A modification of the Weiss reaction was developed to prepare the tetra t-butyl analog 164 of 155. Methylation of 164 with potassium t-butoxide and methyl iodide afforded a mixture of the bis-alkylated products 165, which were hydrolyzed and decarboxylated to afford a 2:1 mixture of the 2,8 and 2,6 regioisomers 170a and 158b, respectively. A mechanism to account for this result has been proposed.;The reaction of 164 with excess potassium hydride and one equivalent of an alkylating agent at ;A computational study was undertaken to access synthetic pathways in going from the stable (5.5.5.5) fenestrane tetraene 20 to pentaene 263 and then to the hexaene 22. It was found that in terms of strain energy, the transformation of 20 to 263 will cost 25-40 kcal and the transformation of 263 to 22 an additional 30-40 kcal. A number of brominated (5.5.5.5) fenestrane polyenes were examined computationally to access their likelihood as potential intermediates in the conversion of tetraene 20 into hexaene 22.;Tetracyclo (5.5.1.0.