Synthesis 2004(1): 128-134  
DOI: 10.1055/s-2003-44351
PAPER
© Georg Thieme Verlag Stuttgart · New York

[3,3]-Sigmatropic Rearrangements in the Enantioselective Synthesis of (-)-Methylenolactocin

Xavier Ariza*, Natalia Fernández, Jordi Garcia*, Marta López, Laia Montserrat, Jordi Ortiz
Departament de Química Orgànica, Div. III, Universitat de Barcelona, C/Martí i Franquès 1-11, 08028, Barcelona, Spain
Fax: +34(93)3397878; e-Mail: jgarcia@qo.ub.es ; e-Mail: xariza@ub.edu;
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Publikationsverlauf

Received 27 October 2003
Publikationsdatum:
25. November 2003 (online)

Abstract

A Pd(II)-catalyzed [3,3]-sigmatropic rearrangement is used to transfer chirality from an enantio-enriched alk-3-ene-1,2-diol to a C 2 -symmetrical alk-2-ene-1,4-diol which, in turn, can be converted into a precursor of (-)-methylenolactocin through an additional [3,3]-sigmatropic rearrangement (either Johnson orthoester or Ireland-Claisen rearrangement).

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In order to assess the stereochemical purity of the product, an analytical sample of diacetate (S,S)-4, was hydrolyzed (NaOMe/MeOH) to diol (S,S)-3. The analysis of the corresponding Mosher diester revealed a 98% ee. Since the analysis of the Mosher diester derived from (S,S)-13 was unclear (signal overlap in 19F NMR and HPLC), we assumed that its optical purity should be ≥98% ee on the basis of that found for (S,S)-3. Absolute configuration of diol 3 revealed it to be identical to that obtained from reduction of diketone 5.