Annulation oxyanion-accelerated

Further studies on the scope and stereochemical course of the oxyanion-accelerated vinylcyclopropane reairangement were reported in 1981. This paper introduced a general [4+1] annulation strategy for the synthesis of cyclopentene derivatives in which the anion-accelerated VCP rearrangement functions as the key step. In this report, the accelerated version of the vinylcyclopropane rearrangement was also shown to proceed with remarkably high stereoselectivity, in further contrast to the thermal process. 

In summary then, the oxyanion-accelerated rearrangement of 2-vinylcyclobutanol derivatives is now established as an attractive method for achieving two-carbon ring expansion under relatively mild conditions. In conjunction with the efficient synthetic routes to vinylcyclobutanones outlined in Scheme 21, this version of the VCB rearrangement provides several strategically novel annulation methods for the construction of six-membered carbocycles. ... 

Strategy C in Scheme 21 employs the [2 + 2] cycloaddition of vinylketenes and 1,3-dienes to generate the requisite 2-vinylcyclobutanone intermediates for oxyanion-accelerated VCB rearrangement. The sequence presented in Scheme 23 illustrates this two-step [4 + 2] annulation strategy, the overall result of... 

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