Asymmetric synthesis of mechanically planar chiral rotaxanes and topologically chiral catenanes has been a long-standing challenge in organic synthesis. Recently, an excellent strategy was developed based on diastereomeric synthesis of rotaxanes and catenanes with mechanical chirality followed by removal of the chiral auxiliary. On the other hand, its enantioselective approach has been quite limited. Here, we report enantioselective preparation of mechanically planar chiral rotaxanes by kinetic resolution of the racemates via remote asymmetric acylation of a hydroxy group in the axis component, which provides an unreacted enantiomer in up to >99.9% ee in 29% yield (the theoretical maximum yield of kinetic resolution of racemate is 50%). While the rotaxane molecules are expected to have conformational complexity, our original catalysts enabled to discriminate the mechanical chirality of the rotaxanes efficiently with the selectivity factors in up to 16.
A highly enantioselective route to a multi-substituted indoline derivative via intramolecular conjugate addition of an -amino acid derivative has been developed.Enantioselectivity of the reaction was almost independent from the temperature, while the diastereoselectivity was totally dependent on the temperature.High diastereomeric ratios observed at the higher temperatures were assumed to be the results from an equilibrium process between axially chiral enolate intermediates.
An enantiocontrolled total synthesis of (+)-heliannuol D has been accomplished using a palladium-catalyzed cyclization of the seven-membered oxygen containing heterocycle as the key reaction.(+)-Heliannuol D (1), 1 isolated by Macías and coworkers from aqueous extracts of fresh sunflower leaves (Helianthus annuus var.SH-222), is a naturally occurring sesquiterpenoid exhibiting allelopathic activity.This intriguing natural product has a unique carbon skeleton made up of an oxygen containing a sevenmembered heterocycle fused to the aryl ring and two tertiary stereogenic centers (C-7 and 10) whose absolute configurations were determined to be R and S, respectively, by our enantioselective total synthesis of (-)-heliannuol D, 2 the unnatural enantiomer.Here we report the first enantiocontrolled total synthesis of the natural enantiomer (+)-heliannuol D (1) starting from (-)-xanthorrhizol (2). 3 In a previous paper, we reported an enantioselective total synthesis of (-)-xanthorrhizol (2), 4 a biologically active aromatic bisabolene sesquiterpenoid, employing lipase-catalyzed desymmetrization of the s-symmetrical prochiral 2-aryl-1,3-propanediol leading to the formation of the optically active alcohol (3) as the key step
Abstract This paper reviews a method of examining the Pockels effect in small and thin flakes of organic material, and discusses the possibility of further improving the Pockels effect in organic materials in terms of the molecular orbital method. The electro-optic coefficient r33 of the styrylpyridinium cyanine dye (SPCD) crystal was estimated from the AC modulation method to be about 430 pm/V at a wavelength λ of 633 nm, 6 times larger than the r11 of 2-methyl-4-nitroaniline (MNA). To improve the Pockels effect further, artificial molecules with a polydiacetylene structure were designed. By adjusting conjugated lengths and donor- and acceptor-substitution sites in the molecules, a large second-order hyperpolarizability was obtained, corresponding to an electro-optic coefficient about 10 times larger than r11 of MNA at a detuning energy of 0.2 eV.
Abstract The first example of a formal [4 + 2] cycloaddition of 3‐ethoxycyclobutanones with quinolines, pyridines, and isoquinolines to give 9a‐hydro‐2H‐quinolizin‐2‐ one derivatives is reported.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Abstract Die Reaktion von Diphenylsulfimid (I) mit den elektrophilen trans‐Olefinen (II) oder ihren cis‐Isomeren (Molverhältnis (I) :(II) = 1.2) führt stets zu den trans‐Aziridinen (III); neben (IIIa) bzw. (IIIb) entstehen auch die trans‐Enaminoketone (IVa) bzw. (IVb) Mit einem Überschuß cis‐Dibenzoylethylen reagiert (I) zu (IIIa) (15% Ausb.) und (IVa) (34%), wobei das nicht umgesetzte Olefin als 31:22‐cis/trans‐Gemisch erhalten wird.
Abstract The carbon‐carbon bond in three‐membered ring of 2,3‐diaryl aziridines was reductively cleaved to give the corresponding dibenzylamine derivatives by electrocyclic ring opening of N ‐Li or N ‐Na aziridines followed by reduction of the 2‐azaallyl anion formed with sodium borohydride in ethanol. Hydrocyanation of the 2‐azaallyl anion with trimethylsilyl cyanide gave a secondary amine bearing a cyano group at the benzylic position. The effects of substituents on the electrocyclic ring opening of N ‐Li aziridines were also clarified.
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