Abstract-Formal synthesis of the telomerase inhibitory marine pyrrolocarbazole alkaloid dictyodendrin B is described. The key features are consecutive palladium-catalyzed cross-coupling reactions and intramolecular reductive coupling reaction to construct the pyrrolo[2,3-c]carbazole framework.
The development of the first intermolecular
Rh2(II)-catalyzed
aziridination of olefins using anilines as nonactivated N atom precursors
and an iodine(III) reagent as the stoichiometric oxidant is reported.
This reaction requires the transfer of an N-aryl
nitrene fragment from the iminoiodinane intermediate to a Rh2(II) carboxylate catalyst; in the absence of a catalyst only diaryldiazene
formation was observed. This N-aryl aziridination
is general and can be successfully realized by using as little as
1 equiv of the olefin. Di-, tri-, and tetrasubstituted cyclic or acylic
olefins can be employed as substrates, and a range of aniline and
heteroarylamine N atom precursors are tolerated. The Rh2(II)-catalyzed N atom transfer to the olefin is stereospecific as
well as chemo- and diastereoselective to produce the N-aryl aziridine as the only amination product. Because the chemistry
of nonactivated N-aryl aziridines is underexplored,
the reactivity of N-aryl aziridines was explored
toward a range of nucleophiles to stereoselectively access privileged
1,2-stereodiads unavailable from epoxides, and removal of the N-2,4-dinitrophenyl group was demonstrated to show that
functionalized primary amines can be constructed.
Please cite this article as: Tanifuji, R., Oguri, H., Koketsu, K., Yoshinaga, Y., Minami, A., Oikawa, H., Catalytic asymmetric synthesis of the common amino acid component in the biosynthesis of tetrahydroisoquinoline alkaloids, Tetrahedron Letters (2015), doi: http://dx.
Previously we developed a promising synthetic approach to complex polycyclic natural products, including aromatic polyketides derived from the type-II polyketide biosynthesis. The approach consists of three key steps; (1) cycloaddition or cyclocondensation of nitrile oxide for assembling the carbon skeleton having an isoxazole as a 1,3-diketone equivalent, (2) benzoin cyclization for stereoselective ring fusion with an angular hydroxy group, and (3) oxidation of isoxazolium salt for installing an additional angular hydroxy group in stereoselective manner. As a synthetic exercise to highlight the utility of this approach, the first total syntheses of the proposed structure of pleospdione (1) and its C3-epimer (3-epi-1) have been achieved. The synthesis has proved the efficiency of the strategy as an entry into polyketide-derived complex architectures.At the same time, it was revealed that neither 1 nor 3-epi-1 represent the true structure of the natural product by incongruity of the NMR spectra.
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