Cope rearrangements seven-membered ring synthesis

A detailed description of the numerous examples of vinylcyclopropropanes used in transition metal mediated organic synthesis is far beyond the scope of this section and can be found in several reviews. Prominent examples are conversions to open-chain products, as well as formation of four-, five-, six- and seven-membered rings via ring expansion or incorporation of other substrates such as carbon monoxide, alkenes or alkynes. Thus divinylcyclopropanes, obtainable via transition metal catalyzed cyclopropanation reactions, undergo a facile thermal Cope rearrangement to form cycloheptadienes. ... 

Eight-membered rings can be obtained by [4+4]-cycloadditions of 1,3-dienes [1] via diradicals or other intermediates. Synthesis of such compounds has been achieved by thermal, [2] photochemical, [3] and by metal-catalyzed [4] processes these reactions have been the subject of extensive mechanistic [5] and theoretical [5c] studies. Their strategic applications in natural product synthesis have been reviewed. [5d] The thermal version has generated little interest, except in orthoquino-dimethane dimerizations and in cycloreversions the Cope rearrangement of 1,2-divinyl-cyclobutanes [3] is more commonly used. [4+4]-Cycloadditions are also used with 1,3-dipoles or mesoionic heterocycles for the synthesis of six- and seven-membered rings. Sometimes also [6+4]-cycloadditions are... 

Another tandem synthesis based on rhodium-carbene complexes, the cyclo-propanation-Cope rearrangement sequence 8-68, was extensively investigated by Davies and coworkers (review Davies, 1993). This sequence leads to cyclohepta-dienes (8.154), which are useful for the synthesis of important natural products containing densely functionalized seven-membered rings. The sequence 8-68 requires ready access to 3-diazoalk-l-enes (vinyldiazomethanes) as basis for the rhodium-... 

In recent years, the synthetic utility of the cyclopropyl-Cope rearrangement has expanded exponentially as a result of new chiral organometallic catalysts which allow for the efficient, stereoselective formation of the required cw-divinylcyclopropanes. " One of the leaders in this area is Davies, who has repeatedly demonstrated the successful tandem cyclopropanation/Cope rearrangement between vinyldiazoacetates and dienes for the synthesis of functionalized seven-membered rings. 

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