Asymmetric Total Syntheses of Aspidodasycarpine, Lonicerine, and the Proposed Structure of Lanciferine

Aspidodasycarpine and lonicerine are a pair of epimeric aspidophylline-type alkaloids bearing vicinal quaternary C7 and C16. The first and enantioselective total syntheses of these molecules are described here. A Ru-catalyzed asymmetric transfer hydrogenation established the first stereocenter. An Au-promoted Toste cyclization was exploited to assemble the bridged tetracyclic core and define the geometry of the exocyclic olefin; electron deficient (p-CF3C6H4)3P was a suitable ligand for this transformation. An aldol condensation followed by an intramolecular indole C3 alkylation constructed the adjacent quaternary C7 and C16 diastereoselectively, leading to a pentacyclic lactol as an advanced common intermediate for synthesizing both alkaloids. The proposed structure of lanciferine, a highly oxidized congener of aspidodasycarpine, was synthesized from the lactol by tuning the oxidation states of various carbons.

Venalstonine and dioxokopsan derivatives from Kopsia fruticosa

Two new venalstonine derivatives, viz., venacarpines A and B, and one new dioxokopsan derivative, kopsorinine, in addition to the kopsifolines A-F, and 11 other known alkaloids, were isolated from a Malayan Kopsia species. The structures of the new alkaloids were determined using NMR and MS analysis.

Scope and limitation of organocuprates, and copper or nickel catalyst-modified Grignard reagents for installation of an alkyl group onto cis-4-cyclopentene-1,3-diol monoacetate

Alkylation of the title compound 1 was investigated with two types of reagents. One is a copper reagent derived from R(T)MgX (X = Cl, Br) and CuX (X = CN, I) and the other is R(T)MgX in the presence of a copper or a nickel catalyst. First, butylation was studied with BuCu(CN)(MgX), Bu(2)Cu(CN)(MgX)(2), BuMgX/CuCN (10 mol %), BuCu (derived from BuMgCl and CuI), and BuMgCl/CuI (10 mol %) in THF or Et(2)O. We found that trans 1,4-isomer 2a and/or trans 1,2-isomer 3a were produced exclusively with these reagents and that the stoichiometry of BuMgX/CuX and the choice of solvent were critical to attain high regioselectivity and efficient yield. Reaction with Bu(2)Cu(CN)(MgCl)(2) and BuMgCl/CuX (X = CN, I; 10 mol %) both in THF produced 2a with 93-94% regioselectivity in 87-92% yields. On the other hand, BuCu(CN)(MgX) in THF, Bu(2)Cu(CN)(MgX)(2) in Et(2)O, and BuMgX/CuCN (10 mol %) in Et(2)O furnished 3a in good yields with >90% selectively, irrespective of X of BuMgX. In the nickel-catalyzed butylation of 1 with BuMgCl, NiCl(2)(dppp) among NiCl(2)(tpp)(2), NiCl(2)(dppf), and NiCl(2)(dppp) furnished the best result to produce 2a. The CuCN-based protocol was then applied to other alkyl Grignard reagents, which include Me, Et, (CH(2))(3)Ph, c-C(6)H(11), (CH(2))(6)OMOM, (CH(2))(9)CH=CH(2), and CH(2)Ph as the alkyl group (R(T)). In addition, the Mitsunobu inversion of 2a and 3a afforded the corresponding cis isomers stereoselectively with AcOH as an acid at -78 degrees C in toluene for 2a and with 4-(NO(2))C(6)H(4)COOH in THF at r.t. for 3a. No racemization during the alkylation was confirmed by the reaction using (1R,3S)-1 (>99% ee) to produce (1S,4S)-2a and (1S,2S)-3a, respectively.