Cope ring enlargement

Furthermore, the oxy-Cope rearrangement of allenic cycloheptane alcohol 47 (NaOEt, THF, 20 °C, 12 h, 80%) gave rise only to ring-enlarged product 48 without transannular cyclization (equation 15)29. The above transformations can be rationalized either by the fragmentation-recombination mechanism or by a concerted oxy-Cope mechanism29. 

The major disadvantages in the application of the Cope rearrangement to the synthesis of organic molecules is the equilibrium between starting material and ring enlargement product. The ratio of the two products is not predictable, a priori. 

If the oxy-Cope rearrangement is carried out with divinyl diols of type V/27 or V/30 (Scheme V/5), ring-enlarged 1,6-diketones of type V/28 or V/31 are produced [18] [19] [20] [21]. Depending on the ring size of the resulting dike-... 

Ring enlargement by the hetero-Cope-rearrangement of (104) afforded (105) in 82% yield <84ZAAC(510)123>. The compound (104) was prepared in two steps from norbomene dicarboxyUc dichloride and phenylbis(trimethylsilyl)phosphine. 

The carbonyl produced in the oxy-Cope rearrangement leads naturally to its coupling with other C-C bond forming processes. A fortuitous discovery of such a process revealed itself in the thermal rearrangement of 89. Expecting a ring enlargement, the authors were surprised to isolate 91, the product of a transannular ene reaction of oxy-Cope product 90. 

Thermolysis of 1,5-dien-3-ols (290) leads either to Cope rearrangement (a) or to 1,5-hydrogen shift reaction products (b). These pathways are both observed in rearrangement of l,2-divinylcycloalkane-l,2-diols the former leads to ring enlargement by four carbon atoms [(291) (292)]. ... 

A common application of the Cope rearrangement is in ring-enlargement sequences. Fill in the reagents and products missing from the following scheme, which illustrates the construction of a 10-membered ring. 

Attempts have been made to find reaction sequences which allow the introduction of more than four atoms into a ring by a Cope rearrangement. Two of these methods should be mentioned, both quite different. The first method uses an enlarged Cope system , which forms bigger rings than the normal Cope system. In the second method the product of one Cope rearrangement can be easily transformed into the starting material for a second Cope shift sequence. 

The position of the Cope equilibrium in 3,4 rearrangements of 1,2-divinylcycloalkanes largely depends on the ring size. In the case of 1,2-divinylcyclopropanes and cyclobutanes, the equilibrium lies on the side of the enlarged rings. For 1,2-divinylcyclopentanes, cyclohexanes, and cycloheptanes, the equilibrium of the Cope rearrangement is reversed, but use of the irreversible... 

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