Cope rearrangements eight-membered ring synthesis

As an application of this procedure, Snapper succeeded in the formal total synthesis of (+)-astericanolide. Treatment of iron complex 62, which is prepared from cyclopentenol derivative 60 and iron complex 61, with MeaNO gives fused cyclobutene derivative 63. ROM of cyclobutene of 63 using Ig under ethylene gas smoothly proceeds to produce an eight-membered ring of 64 via Cope rearrangement. The resulting product 64 is converted into Wender s intermediate for the synthesis of (+)-astericanolide ... 

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... 

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