Syntheses of Theaspirone and Vitispirane via Palladium(II)-Catalyzed Oxaspirocyclization.
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.
Nilsson
Ylva I. M.
YI
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.
Aranyos
Attila
A
Andersson
Pher G.
PG
Bäckvall
Jan-E.
JE
Parrain
Jean-Luc
JL
Ploteau
Christelle
C
Quintard
Jean-Paul
JP