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Studies related to the preparation of 2-alkyl- and 2-alkenyl-1,3-cyclohexanediones ; An investigation into the regioselective formation of -IODO ,-unsaturated ketones from unsymmetrical 1,3-cyclohexanediones ; Studies related to the divinylcyclopropane rearrangement

University of British Columbia

The work described in this thesis is devoted to three separate synthetic methods studies, which represent some past and current interests in our laboratory. In the first study, a preparation of 2-alkyl- and 2-alkenyl-1,3-cyclohexanediones (2) from 1,5-dimethoxy-1,4-cyclohexadiene (14) is described. Metalation of the diene (14) with tert-butyllithium in tetrahydrofuran solution at low temperature (-78°C) followed by addition of an alkyl or alkenyl halide, in the presence of hexamethylphosphoramide, resulted in a completely regioselective alkylation reaction affording the corresponding 6-alkyl- or 6-alkenyl-1,5-dimethoxy-1,4-cyclohexadiene (16). The latter substances were isolated in good to excellent yields. Simple aqueous hydrolysis of these materials in the absence of air afforded the desired 2-alkyl- and 2-alkenyl-1,3-cyclohexanediones (2) in good yields. In the second study, an investigation into the regioselective formation of β-iodo α,β-unsaturated ketones (e.g., (64) and (65)) from unsym-metrical 1,3-cyclohexanediones (63) employing triphenylphosphine diiodide-triethylamine in acetonitrile is described. It has been found that when one of the carbonyl functionalities of the substrate is quite steric-ally hindered the reaction is nearly completely regioselective. In the third study, the thermal (Cope) rearrangement of the bicyclic dienes (136a), (136b-E), and (136b-2) and the tricyclic dienes (137a-d) is described. In each case, thermolysis of the substrate at 240°C followed by hydrolysis of the intermediate product thus obtained afforded a bicyclo-[3.2.2]non-6-en-3-one, ketones (148), (149), (150) and (151a-d), respectively, in fair to good overall yield (49-81%).

Text

2010-05-02

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http://hdl.handle.net/2429/24295

Chemistry

University of British Columbia

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