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Synlett 2000; 2000(8): 1111-1114
DOI: 10.1055/s-2000-6740
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Asymmetric Synthesis of Polycyclic Polyketides via the Double Diels-Alder Addition of 2,2′-Ethylidenebis[3,5-dimethylfuran]

Chiara Marchionni* , Kai Meilert, Pierre Vogel, Kurt Schenk
  • *Section de Chimie de l'Université, BCH, CH-1015 Lausanne-Dorigny, Switzerland; Fax+ 41 21 692 39 75; E-mail: pierre.vogel@ico.unil.ch
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Publication Date:
31 December 2000 (online)

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The Diels-Alder adduct 3 of 2,2′-ethylidenebis (3,5-dimethylfuran) to diethyl (E,E)-4-oxohepta-2,5-diene-1,7-dioate was converted into meso-(1R,2R,4R,4aR,5S,7 S,8S,8aS,9aS,10s,10aS)-1,8-bis(acetoxymethyl)-1,3,4,5,6,7,8,8a,9,9a-decahydro-2,4,5,7,10-pentamethyl-3,6,9- trioxo-2H,10H-2,4a:7,10a-diepoxyanthracene (9). Enantioselective monoreduction of 9 with BH3 · Me2S and a catalytic amount of methyloxazaborolidine derived from l-diphenylprolinol gave (-)-(1S,2S,4S,4aS,5S,6R,7R,8R,8aS,9aR,10R,10aS)-1,8-bis(acetoxymethyl-1,3,4,5,6,7,8,8a,9,9a-decahydro-6-hydroxy-2,4,5,7,10-pentamethyl-3,9-dioxo-2H,10H-2,4a:7,10a-diepoxyanthracene ((-)-11) with 90% ee. Its absolute configuration was established by single crystal X-ray diffraction studies of the camphanate (-)-13 (1S,2S,4S,4aS,5S,6S,7R,8R,8aS,9aR,10R,10aS)-8-acetoxymethyl-1-[(2′S,5′R)-camphanoyloxymethyl]-1,3,4,5,6,8,8a,9,9a-decahydro-6-(methoxymethyl)-2,4,5,7,10-pentamethyl-3,9-dioxo-2H,10H-2,4a:7,10a-diepoxyanthracene). Basic treatment of (-)-10 led to regioselective ethereal ring opening of the 7-oxabicyclo[2.2.1]heptan-2-one moiety at C-1,2,3,4,4a,9a with formation of (1R,2R,3R,4S,4aR,5S,7S,8S,9aS,10S)-1,8-diacetoxymethyl-1,3,4,5,6,7,8,9,9a,10-decahydro-3,7-dihydroxy-2,4,5,7,10-pentamethyl-6,9-dioxo-2H-2,4a-epoxyanthracene. Thus desymmetrization of 9 via enantioselective triketone reduction allows the preparation of polycyclic polyketides with high stereochemical complexity and with high stereo- and enantioselectivity.

Diels-Alder addition - double-chain elongation - 7-oxabicyclo[2.2.1]heptanes - polyketides - polypropionates