| Title
| - Synthesis of 2,3-Dihydro-3-hydroxy-2-hydroxylalkylbenzofuransfrom Epoxy Aldehydes. One-Step Syntheses of Brosimacutin G,Vaginidiol, Vaginol, Smyrindiol, Xanthoarnol, and Avicenol A.Biomimetic Syntheses of Angelicin and Psoralen
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| Abstract
| - We have developed two practical one-step syntheses of 2,3-dihydro-3-hydroxy-2-hydroxyalkylbenzofurans from readily available optically pure α,β−epoxy aldehydes. Electron-deficient resorcinolsreact with epoxy aldehydes using either Cs2CO3 in DMF or KOH/CaCl2 in MeOH to give adducts13, 16, 18, 20, 21, and brosimacutin G (6t). Grignard reagents prepared by low-temperaturehalogen−metal exchange of acetoxy iodocoumarins 35d and 40 and acetoxy bromonaphthalene 41add to epoxy aldehyde (S)-26 to complete the first syntheses of vaginidiol (7c), vaginol (7t),smyrindiol (8c), xanthoarnol (8t), and avicenol A (9t). Acid-catalyzed fragmentation of vaginidiolor vaginol provides angelicin, while that of smyrindiol or xanthoarnol affords psoralen. In bothcases, the trans isomers fragment only twice as fast as the cis isomers, possibly through theintermediacy of a common benzylic cation. This may have implications for the biosynthesis ofangelicin and psoralen.
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