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Chromium-Mediated Dearomatization: Application to the Total Synthesis of Racemic 15-Acetoxytubipofuran and Asymmetric Synthesis of Both Enantiomers

Authors
Laxmisha, Mundruppady S.
Ronggang, Liu
Published in Helvetica Chimica Acta. 2005, vol. 88, no. 5, p. 1063-1080
Abstract An efficient dearomatization process of [Cr(arene)(CO)3] complexes initiated by a nucleophilic acetaldehyde equivalent is detailed. It generates in a one-pot reaction three C--C bonds and two stereogenic centers. This process allowed a rapid assembly of a cis-decalin ring system incorporating a homoannular diene unit in just two steps starting from aromatic precursors (Scheme 2). The method was applied to the total synthesis of the eudesmane-type marine furanosesquiterpene (±)-15-acetoxytubipofuran (2). Two routes were successfully used to synthesize the ?-lactone precursor of the furan ring. The key step in the first approach was a Pd-catalyzed allylic substitution (Scheme 3), while in the second approach, an Eschenmoser-Claisen rearrangement was highly successful (Scheme 4). The Pd-catalyzed allylic substitution could be directed to give either the (normal) product with overall retention as major diastereoisomer or the unusual product with inversion of configuration (see Table). For the synthesis of the (-)-enantiomer (R,R)-2 of 15-acetoxytubipofuran, an enantioselective dearomatization in the presence of a chiral diether ligand was implemented (Scheme 7), while the (+)-enantiomer (S,S)-2 was obtained via a diastereoselective dearomatization of an arene-bound chiral imine auxiliary (Scheme 8). Chiroptical data suggest that a revision of the previously assigned absolute configuration of the natural product is required.
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KUNDIG, Ernst Peter et al. Chromium-Mediated Dearomatization: Application to the Total Synthesis of Racemic 15-Acetoxytubipofuran and Asymmetric Synthesis of Both Enantiomers. In: Helvetica Chimica Acta, 2005, vol. 88, n° 5, p. 1063-1080. https://archive-ouverte.unige.ch/unige:7837

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Deposited on : 2010-06-21

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