Syntheses of Theaspirone and Vitispirane via Palladium(II)-Catalyzed Oxaspirocyclization |
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| Authors: | Nilsson Ylva I M Aranyos Attila Andersson Pher G Bäckvall Jan-E Parrain Jean-Luc Ploteau Christelle Quintard Jean-Paul |
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| Institution: | Department of Organic Chemistry, University of Uppsala, Box 531, S-751 21 Uppsala, Sweden, and Laboratoire de Synthèse Organique associé au CNRS, Faculté des Sciences et des Techniques de Nantes, 2 rue de la Houssinière, 44072 Nantes, Cedex 03, France. |
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| Abstract: | Total syntheses of theaspirone (A and B) and vitispirane (A and B) are described. The key step in the syntheses is the palladium(II)-catalyzed intramolecular oxaspirocyclization of diene alcohol 4 to either vitispirane or the allylic alcohol 9. The outcome of the oxaspirocyclization is very much dependent on the solvent employed. In water-acetic acid (4:1) a 1:1 mixture of the diastereomeric alcohols 9A and 9B was exclusively formed. In water with 8 equiv of a strong non-nucleophilic acid, vitispiranes A and B (1:1) were obtained. An alternative procedure to obtain vitispirane with the use of LiCl and K(2)CO(3) is described. In the latter reaction vitispirane B is formed preferentially. This result is explained by an equilibrium between the two possible pi-allyl complexes 5A and 5B, the kinetically favored 5B being transformed into vitispirane 3B before isomerization to 5A occurs. |
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