“Truncated” Pagodanes — Synthesis of Functionalized [1.1.1.1] and [1.1.1.0] Pagodanes

Abstract “Truncated” [1.1.1.1] pagodanes like the [1.1.0.0] and [0.0.0.0] homologues3 and 4 (E Str = 146.1 – 171.5 kcal mol −1 , MM2) are potential precursors of unusual unsaturated homoconjugated radical cations and σ‐bishomoaromatic dications. Attempts are presented toward the synthesis of 3 ‐ starting out from [1.1.1.1] pagodane‐4,9‐dione 9 and diaza [2.2.1.1] pagodadiene 11 by cycloelimination (unsuccessful) and by Favorskii‐type ring contraction methodologies. Control experiments with the model diketone 19 documented the limitations for α,α′‐difunctionalization of 9 as the prerequisite for one‐pot double Favorskii‐type ring contraction. A de novo synthesis for such α,α′‐disubstituted derivatives of 9(54) was not sufficiently expeditious to open a practical access to 3. Sequential double bridgehead hydroxylation of 9, successfully practized with model 19, similarly suffered from inherent cage effects and allowed only limited yields of [1.1.1.0] pagodanone 10, the intermediate on the way to 3.