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Anionic rearrangements of 4-hydroxycyclohex-2-en-1-ones

University of British Columbia

The base-induced chemistry of three enone-alcohols, 1,6-di- cyano-8,9-dimethyl-5-hydroxytricyclo[4.4.0.0[sup 5,9]]deca-3,7-dien-2- one (48) , 8 , 9-dimethyl-5-hydroxytricyclo [4.4.0.0[sup 5,9]]deca-3,7- dien-2-one (24), and 1,3,4,6,8,9-hexamethyl-5-hydroxytricyclo- [4.4.0.0[sup 5,9]] deca-3,7-dien-2-one (3) , has been investigated. The inertness of 3 under the reaction conditions (potassium hydroxide, refluxing aqueous dioxane) that converts 1,3,4,6,8,9-hexamethyl- tricyclo[4.4.0.03,10]dec-8-ene-2,5-dione (1) into 1,3,4,6,8,9- hexamethyltricyclo [4 .4.0 .0[sup 3,7]] dec-8-ene-2 , 5-dione (2) indicated that 3 is not a major intermediate in such conversion. Restriction in conformational isomerism due to the bulky bridgehead methyl groups is believed to be the main reason for prohibiting the rearrangement of 3 to 2. Under more vigorous reaction conditions (potassium hydride, refluxing dimethoxyethane (DME)), however, enone-alcohol 3 rearranged to give diketone 2 and twistane deriva- tive 28, 1,3,4,6,8,9-hexamethyltricyclo[4.4.0.0[sup 3,8]]dec-9-ene-2,5- dione, which slowly rearranged under the reaction condition to its exo-methylene isomer 29, 1, 3, 4 , 6, 8-pentamethyl-exo-9-methylene- tricyclo[4.4.0.0[sup 3,8]]decane-2,5-dione. When enone-alcohol 24 was t treated with KH at room temperature in DME, diketone 19, 8,9-di- methyltricyclo[4.4.0.0[sup 3,7]]dec-8-ene-2,5-dione, was produced. Similar treatment of enone-alcohol 48 with KH at room temperature in DME resulted in the formation of 8,9-dicyano-1,6dimethyltri-cyclo [4.4.0.0'[sup 3,7]]dec-8-ene-2,5-dione (50). Although diketones 19 and 50 have identical ring skeletons, the difference in their substituent patterns shows that they are formed by different mechanisms. Ring opening of the corresponding alkoxide is suggested as the initial step in all three reactions, and the divergent results were explicable on the basis of the substituent-controlled direction of ring opening in addition to product control through restriction of rotation of the intermediates so produced.

Text

2010-03-19

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http://hdl.handle.net/2429/22192

Chemistry

University of British Columbia

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