Divergence en route to nonclassical annonaceous acetogenins. Synthesis of pyranicin and pyragonicin |
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Authors: | Strand Daniel Norrby Per-Ola Rein Tobias |
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Institution: | KTH Chemical Science and Engineering, Organic Chemistry, SE-100 44 Stockholm, Sweden. |
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Abstract: | Syntheses of the nonclassical annonaceous acetogenins, pyranicin, and pyragonicin from common late-stage intermediates are presented. The construction of key elements relies on asymmetric HWE reactions, including the desymmetrization of a meso-dialdehyde and a parallel kinetic resolution of a racemic aldehyde. A stereoconvergent Pd-catalyzed substitution serves to install the C4 stereocenter in protected form with different orthogonal protective groups. A divergent strategy to form 1,4- and 1,6-diols, employing stereoselective Zn-mediated alkynylations, is used for completion of the core structures. Notably, the stereoselective coupling reaction toward pyragonicin proceeds with highly functionalized fragments. The methodology is further expanded by a divergent synthesis of all stereoisomers of the 2,3,6-trisubstituted tetrahydropyran subunit. |
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