Qin XL, Wu GJ, Han FS. Synthetic Studies on the Synthesis of Toxicodenane A and 8,11-
epi-Toxicodenane A.
J Org Chem 2022;
87:3223-3233. [PMID:
35041787 DOI:
10.1021/acs.joc.1c02928]
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Abstract
The diverse synthesis of oxatricyclotridecanes and oxatricyclododecanes, which are the core structures of toxicodenane A and its skeletal analogues, via a unified manner is presented. The stereochemistry at the bridgehead position of the oxa-bridged bicycle could be efficiently controlled through a diastereoselective anti- and syn-Grignard allylation reaction by appropriately tuning the reaction conditions such as the solvent, the counterion of the Grignard reagent, the substrate, or a combination of these. The ring size could be precisely elaborated via a Lewis acid-mediated intramolecular transacetalation and Prins cyclization cascade reaction by varying the steric hindrance of olefin moiety. Namely, substrates bearing a terminally unsubstituted olefinic functionality afforded oxatricyclotridecanes with an overwhelming preference, while those bearing a dimethyl-substituted olefinic group produced exclusively oxatricyclododecanes. The wide utility and generality of the above key transformations are highlighted by the applications in the unified synthesis of (±)-toxicodenance A, (+)-toxicodenane A, (+)-8,11-epi-toxicodenane A, and other oxatricyclic cores with different stereochemistries and ring sizes.
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