Synthesis 2002(14): 1993-2012
DOI: 10.1055/s-2002-34386
PAPER
© Georg Thieme Verlag Stuttgart · New York

Oxabicyclo[3.2.1]oct-6-enes as Templates for the Stereoselective Synthesis of Polypropionates: Total Synthesis of Callystatin A and C19-epi-Callystatin A

Mark Lautens*, Timothy A. Stammers
Davenport Research Laboratories, Department of Chemistry, University of Toronto, Toronto, Ontario, M5S 3H6, Canada
Fax: +1(416)9786083; e-Mail: mlautens@chem.utoronto.ca;
Further Information

Publication History

Received 16 June 2002
Publication Date:
26 September 2002 (online)

Abstract

The total synthesis of the polyketide natural product callystatin A and its novel analog C19-epi-callystatin A is described. Our strategy features the use of an enantiomerically pure oxabicyclo[3.2.1]oct-6-ene as a template for the stereocontrolled preparation of the C15-C21 polypropionate region.

36

We independently found the same solution to the olefination problem of intermediate 25/B as was reported recently in the literature. [12a] [35]

37

Alternatively, diol 27 could also be prepared from intermediate 19 (Scheme [19] ).

44

(E)-Enal (Scheme [20] ) was consistently isolated from the MnO2 allylic oxidation in approximately 4% yield. This material could be recycled by stirring in 2-propanol and PPTS, forming 38 in modest yield.

47

Ratio determined by comparing isolated yields and tert-butyl signals on the 1H NMR spectra of the mixed fractions of mono-silylated products. An accurate measurement of the ratio could not be based on the crude 1H NMR.