Enantioselective Sulfoxide-directed Preparation of 1,2-diols from Oxalic Compounds: Formal Synthesis of the 10-Membered Lactone Core of Ascidiatrienolides and Didemnilactones.

The synthesis of diene 17, which is available in both possible absolute configurations is described. This diene constitutes the key intermediate of a previous synthesis of the 10-membered lactone core of the marine natural products ascidiatrienolides and didemnilactones. This intermediate is available via two successive highly diastereoselective sulfoxide-directed reductions of oxalic diamide 18

A Concise and Efficient Stereoselective Synthesis of the C1-C11 Fragment of Macrolactin A

A stereoselective synthesis of the C1–C11 fragment of macrolactin A, using original approaches for the introduction of the Z,E-diene stereochemistry and the C-7 stereogenic center, is reported. The adopted strategy has allowed us to build up the fragment by the assembly of three key intermediates via cross-metathesis, Still–Gennari, and Wittig olefinations. Opening of the commercially available chiral benzyl glycidol epoxide to the corresponding homoallylic alcohol introduced the C-7 chiral center. A cross-metathesis reaction was used to create the C5–C4 E double bond. The Still–Gennari reaction introduced the 2Z,4E-diene moiety and finally the Wittig reaction with a propargylic triphenylphosphorane introduced directly the 1,3-enyne unit in a highly efficient stereoselective fashion

Convergent high stereoselective preparation of the C12-C24 fragment of Macrolactin A.

The convergent synthesis of the C12-C24 fragment (lower part) of macrolactin A is described. The adapted strategy allowed building up the lower moiety by the assembly of three key intermediates via organometallic addition. One hydroxylic stereogenic center was introduced by the application of chiral sulfoxides methodology on fragment C19-C24. The preparation of the versatile 1,3-anti diol synthon C12-C16 was achieved via opening of chiral epoxide and subsequent oxidation to a hydroxy ketone. Finally, reductive elimination of the appropriate allylic dibenzoate with Na/Hg introduced directly the C16-C19 (E,E)-diene unit, in a highly efficient stereoselective fashion