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Synlett 1991; 1991(12): 854-856
DOI: 10.1055/s-1991-20900
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Seven-Membered Ring Chelates as a Tool for Stereocontrol in Intramolecular Diels-Alder Reactions: Application to a Short Synthesis of α-Eudesmol

Barbara Frey* , Siegfried Hünig, Michael Koch, Hans-Ullrich Reissig
  • *Institut für Organische Chemie der Technischen Hochschule Darmstadt, Petersenstrasse 22, D-6100 Darmstadt, Germany
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Publication Date:
07 March 2002 (online)

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5-Methoxycarbonyl-1,7,9-decatrien-3-ones 1,3 and 6-methoxycarbonyl-2,8, 10-undecatrien-4-one 6 underwent smooth intramolecular Diels-Alder reactions selectively providing cis-cycloadducts when diethyl ether-boron trifluoride complex is employed as promoter. On the other hand, Lewis acids such as titanium(IV) bromide or tin(IV) chloride cause preferential formation of trans-octalones (methyl 1,2,3,4,4a,5,6,8a-octahydro-4-oxonaphthalene-2-carboxylates). Seven-membered ring chelates involving a keto group and an ester function as ligands for the Lewis acids with two free coordination sites are suggested as crucial intermediates.