Resorcinols aldol cyclization

With increasing chain lengths the number of possible cyclization products rises rapidly. A tetraketoacid can undergo three aldol condensations, a Claisen and additional heterocyclic ring closures. Some of the initial cyclization products can undergo further cyclization reactions. For instance, ketoacid 78 under treatment with aqueous NaHCOs produces mainly the unstable resorcinol 79, which cyclizes further to give the coumarin 80 (equation 84). With aqueous KOH, the resorcinol 79 became a minor product whereas the isomer 81 is the major product in the reaction . ... 

Our first specific Wessely oxidation approach is outlined in Scheme 2. Following an aldol-type reaction between an appropriately protected resorcinol fragment and an aldehyde, we expected the Wessely oxidation to selectively dearomatize at the ortho position of both phenols. The intramolecular Diels-Alder cycloaddition reaction was then expected to form the tricyclic core, which could then be converted to the critical tetracyclic cage via a samarium diiodide(II)-type 6-exo-trig ketyl radical cyclization reaction. 

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