Catalytic asymmetric reactions in alkaloid and terpenoid syntheses

Catalytic asymmetric induction is one of the most important methods in current synthetic organic chemistry for designing efficient and attractive synthetic routes. The efficient total synthesis of a natural product can be achieved through the identification of appropriate method and strategy. This Letter introduces the catalytic asymmetric syntheses of alkaloids and terpenoids based on an overview of four recently reported types of asymmetric reaction: (1) asymmetric decarboxylative allylation, (2) organocatalytic cascade reaction, (3) polyene cyclization, and (4) asymmetric [2+2]-photocycloaddition catalyzed by a chiral Lewis acid.     

Chiral phosphine-phosphoramidite ligands in asymmetric catalysis

Chiral phosphine-phosphoramidite ligands, featuring ready availability, easy modification, and stability towards air and moisture, have recently emerged as a new kind of robust ligands for asymmetric catalysis. They have been found to display wide utilities in various catalytic asymmetric reactions, giving excellent enantioselectivities in the Rh-, Ru-, and Ir-catalyzed asymmetric hydrogenation of C?C, C?O, and C?N double bonds; Rh-catalyzed asymmetric hydroformylation; Pd-catalyzed asymmetric hydrophosphorylation; Pd-catalyzed asymmetric allylic alkylation; Ag-catalyzed asymmetric [3 + 2] cycloaddition; and Cu-catalyzed conjugate addition and reduction. In this review, the progress on the development of chiral phosphine-phosphoramidite ligands in asymmetric catalysis has been summarized.     

Regioselective cycloaddition reaction of alkene molecules with the asymmetric dimer on Si(100)c(4 x 2)

We investigated the adsorption states of 2-methylpropene and propene on Si(100)c(4 x 2) using low-temperature scanning tunneling microscopy. We have found that regioselective cycloaddition reactions (di-sigma bond formation) occur between the asymmetric alkene molecules and the asymmetric dimers on Si(100)c(4 x 2). First-principles calculations have elucidated that the regioselectivity is closely related to the structures of precursor species and these precursor species have carbocation-like features. Thus, we conclude that Markovnikov's rule is applicable for the cycloaddition of asymmetric alkene with the asymmetric dimer on Si(100)c(4 x 2).     

Gas transport properties of asymmetric polyimide membranes prepared by plasma‐based ion implantation

In this study, we report the gas permeance and selectivity of the asymmetric polyimide membrane prepared by plasma‐based ion implantation (PBII). The asymmetric polyimide membranes were prepared using a dry–wet phase inversion process, and the surface skin layer on the membrane was implantated by He ions at 2.5 keV. The asymmetric membranes treated by PBII were measured using a high vacuum apparatus with a Baratron absolute pressure gauge at 76 cmHg and 35°C. The (O₂/N₂) and (CO₂/CH₄) selectivities in the He⁺‐implanted asymmetric membrane at 60 sec resulted in 1.5 and 1.8 time increases, respectively, when compared to those of the asymmetric membrane before PBII. On the other hand, the O₂ and CO₂ permeances in the asymmetric membrane after PBII decreased with an increase in the He⁺ treatment time. In this paper, we addressed, for the first time, the gas permeation behavior of the asymmetric polyimide membranes prepared by PBII. Copyright © 2009 John Wiley & Sons, Ltd.     

靛红亚胺参与构建手性3-氨基-2-吲哚酮骨架的研究进展

手性3-氨基-2-吲哚酮骨架广泛存在于许多药物分子以及天然产物中,具有较高的药用价值。 靛红亚胺参与的不对称反应是合成手性3-氨基-2-吲哚酮衍生物的直接途径。 本文围绕着不对称aza-Henry反应、不对称环化反应及其他不对称反应3个方面,综述了靛红亚胺参与构建手性3-氨基-2-吲哚酮衍生物的研究进展并进行了展望。     

Copper-catalyzed asymmetric cyclization of alkenyl diynes: method development and new mechanistic insights

Metal carbenes have proven to be one of the most important and useful intermediates in organic synthesis, but catalytic asymmetric reactions involving metal carbenes are still scarce and remain a challenge. Particularly, the mechanistic pathway and chiral induction model in these asymmetric transformations are far from clear. Described herein is a copper-catalyzed asymmetric cyclization of alkenyl diynes involving a vinylic C(sp²)–H functionalization, which constitutes the first asymmetric vinylic C(sp²)–H functionalization through cyclopentannulation. Significantly, based on extensive mechanistic studies including control experiments and theoretical calculations, a revised mechanism involving a novel type of endocyclic copper carbene via remote-stereocontrol is proposed, thus providing new mechanistic insight into the copper-catalyzed asymmetric diyne cyclization and representing a new chiral control pattern in asymmetric catalysis based on remote-stereocontrol and vinyl cations. This method enables the practical and atom-economical construction of an array of valuable chiral polycyclic-pyrroles in high yields and enantioselectivities.

A copper-catalyzed asymmetric cyclization of alkenyl diynes involving a vinylic C(sp²)–H functionalization is reported, enabling the construction of various valuable chiral polycyclic-pyrroles in high yields and enantioselectivities.     

Asymmetric combinational “metal-biocatalytic system”: One approach to chiral 2-subsituted-tetrahydroquinoline-4-ols towards two-step one-pot processes in aqueous media

A novel asymmetric “metal-biocatalytic system”, involving Rh-catalyzed asymmetric transfer hydrogenation and whole cell mediated asymmetric hydroxylation in aqueous buffer, has been achieved. The methodology gives access to 2-subsituted-tetrahydroquinoline-4-ols bearing two stereocenters from 2-subsituted-quinolines in moderate to excellent results (up to 47% yield, 99:1 dr, and >99% ee).     

t-Bu-QuinoxP* ligand: applications in asymmetric Pd-catalyzed allylic substitution and Ru-catalyzed hydrogenation

The potential of the t-Bu-QuinoxP* ligand (1) as a chiral ligand in asymmetric synthesis was examined. The ligand exhibited good to excellent asymmetric induction in Pd-catalyzed asymmetric allylic substitution of 1,3-diphenyl-2-propenyl acetate (up to 98.7% ee) and in Ru-catalyzed asymmetric hydrogenation of ketones (up to 99.9% ee).     

Asymmetric synthesis of (+)-tetrahydropseudodistomin

An efficient asymmetric synthesis of (+)-tetrahydropseudodistomin is described. The important synthetic features include a Maruoka asymmetric allylation and a Sharpless asymmetric dihydroxylation as key steps for the generation of chirality at C-2, -4, and -5 of the trisubstituted piperidine ring.     

Asymmetric synthesis and absolute configuration of streptophenazine G

The asymmetric synthesis of the antibacterial natural product, streptophenazine G, has been achieved by employing asymmetric alkylation and asymmetric aldol reactions using chiral oxazolidinones as the key steps. The originally proposed structure for streptophenazine G has been revised, and its absolute configuration has been determined to be 1'S,2'R,6'S. The asymmetric total synthesis of 6'-epi-streptophenazine G is also described.     

Asymmetric [4+2] cycloadditions employing 1,3-dienes derived from (R)-4-t-butyldimethyl-silyloxy-2-cyclohexen-1-one

1,3-Dienes derived from (R)-4-t-butyldimethylsilyloxy-2-cyclohexen-1-one react with activated dienophiles to form predominately (or sometimes exclusively) syn/endo products. These controlled [4+2] cycloadditions increase the asymmetric complexity from one asymmetric center in the starting material to five asymmetric centers in the products in a single step, and provide a powerful approach for the asymmetric synthesis of compounds containing the bicyclo[2.2.2]octanone carbon skeleton.     

Asymmetric Addition of Diethylzinc to Aldehydes Using SPINOL Derivatives

Lewis acid catalyzed enantioselective carbon-carbon bond formation is one of the most interesting challenges in catalytic asymmetric synthesis. A convenient route for this synthesis is the addition of organozinc to aldehydes.[1]1,1'-Spirobiindane-7,7'-diol (SPINOL), a new reported C2 symmetrical diol, was recently proven to be an excellent framework for chiral ligands.[2] In this paper, interestingly, we describe the preparation of SPINOL derivatives and application of these ligands to asymmetric addition of diethylzinc to aldehydes as model reaction. Previously, an improved method for the resolution of C2-symmetric spirocyclic SPINOL was presented with crude menthyl chloroformate as resolving reagent.[3] Then (R)-SPINOL with C2-symmetric spirocyclic framework was applied in the asymmetric diethylzinc addition to aromatic aldehydes, which induced high conversions and moderate enantioselectivities for the production of chiral secondary alcohols. Further work of other SPINOL derivative ligands for asymmetric diethylzinc addition to aromatic aldehydes and developing further new SPINOL-based Lewis acid catalyzed asymmetric synthesis are underway.     

C2轴不对称联芳香化合物的合成研究进展

概述了近年来Ｃ２轴不对称联芳香化合物的合成与不对称偶联的研究进展。     

Asymmetric total synthesis of (+)-K01-0509 B: determination of absolute configuration

K01-0509 B is a novel natural product which contains a carbamoylated cyclic guanidine. Our asymmetric total synthesis features a Sharpless asymmetric epoxidation and a stereocontrolled construction of the cyclic guanidine via an asymmetric nitroaldol reaction, followed by intramolecular SN2 cyclization. These reactions allowed the cyclic guanidine and the adjacent hydroxy group to be assembled, facilitating the asymmetric total synthesis and determination of the absolute stereochemistry of K01-0509 B. [reaction: see text].     

Asymmetric Morita-Baylis-Hillman reactions catalyzed by chiral Brønsted acids

Chiral BINOL-derived Br?nsted acids catalyze the enantioselective asymmetric Morita-Baylis-Hillman (MBH) reaction of cyclohexenone with aldehydes. The asymmetric MBH reaction requires 2-20 mol % of the chiral Br?nsted acid 2e or 2f and triethylphosphine as the nucleophilic promoter. The reaction products are obtained in good yields (39-88%) and high enantioselectivities (67-96% ee). The Br?nsted-acid-catalyzed reaction is the first example of a highly enantioselective asymmetric MBH reaction of cyclohexenone with aldehydes.     

Catalytic Asymmetric (4+3) Cyclizations of In Situ Generated ortho‐Quinone Methides with 2‐Indolylmethanols

The first catalytic asymmetric (4+3) cyclization of in situ generated ortho‐quinone methides with 2‐indolylmethanols has been established, which constructed seven‐membered heterocycles in high yields (up to 95 %) and excellent enantioselectivity (up to 98 %). This approach not only represents the first catalytic asymmetric (4+3) cyclization of o‐hydroxybenzyl alcohols, but also enabled an unprecedented catalytic asymmetric (4+3) cyclization of 2‐indolylmethanols. In addition, a scarcely reported catalytic asymmetric (4+3) cyclization of para‐quinone methide derivatives was accomplished.     

无溶剂条件下的不对称催化反应

本文综述了近年来在无溶剂条件下进行的一些不对称催化反应的进展, 着重介绍了无溶剂条件下的不对称Aldol反应、环氧化合物不对称开环反应、外消旋环氧化合物的拆分、不对称Diels-Alder反应、金属有机试剂对醛酮的不对称加成反应、不对称氢化反应、不对称氢甲酰化反应、不对称烯烃复分解反应、不对称Michael加成反应、不对称氧化反应、不对称Friedel-Crafts反应等, 同时展望了无溶剂不对称催化反应的研究前景。     

One-step synthesis of organic-inorganic hybrid asymmetric dimer particles via miniemulsion polymerization and functionalization with silver

Organic-inorganic polystyrene (PSt)-silica (SiO2) hybrid asymmetric particles were prepared in one step by a miniemulsion polymerization technique. The organic and inorganic reagents were confined in miniemulsion microreactor droplets. After the formation of PSt and SiO2, internal phase separation inside the droplets was accelerated owing to the hydrophobicity of PSt and the hydrophilicity of SiO2. Therefore, PSt-SiO2 hybrid asymmetric particles could be synthesized in one step. Between each pair of asymmetric particles, silane couplers act as bridges connecting the PSt and SiO2 particles. The size of PSt particles in these asymmetric particles was easily tuned either by changing the weight ratio of St/TEOS or by varying the sonication power during the miniemulsion preparation. After functionalization of the as-prepared asymmetric dimers by surface decoration with Ag particles, enhanced surface-enhanced Raman scattering (SERS) properties were observed due to electromagnetic enhancement of the added Ag colloids.     

Two 3-D Neutral Zn(Ⅱ)-MOFs Generated from the Asymmetric Schiff-base Ligand

Two new Zn(Ⅱ)-MOFs were synthesized based on an asymmetric Schiff-base ligand LH, which is obtained by the condensation of 5-formyl-8-hydroxyquinoline and 3-pyridinecarboxylic acid hydrazide. In different mixed solvents, we get two new isomorphism compounds, [Zn(L)2]·C4H8O2·2MeOH(1) and [Zn(L)2]·CH2Cl2·2MeOH(2). Compounds 1 and 2 have been characterized by single-crystal X-ray diffraction, elemental analysis and IR. Compound 1 crystallizes in monoclinic, space group P21/c, with a = 13.856(4), b = 14.156(4), c = 9.620(3) , β = 110.167(5)°, V = 1771.3(9) 3, Dc = 1.500 g/cm3, C38H38N8O8 Zn, Mr = 800.13, F(000) = 832, μ(MoKα) = 0.761 mm-1, Z = 2, the final R = 0.0596 and wR = 0.1221 for 2112 observed reflections(I 2σ(I)). Compound 2 belongs to monoclinic, space group P21/c, with a = 13.575(3), b = 14.130(3), c = 9.485(2) , β = 107.908(3)°, V = 1731.2(6) 3, Dc = 1.529 g/cm3, C35H32Cl2N8O6 Zn, Mr = 796.96, F(000) = 820, μ(MoKα) = 0.926 mm-1, Z = 2, the final R = 0.0527 and wR = 0.1395 for 2501 observed reflections(I 2σ(I)). The Zn(Ⅱ) centers in both 1 and 2 display a distorted octahedral coordination geometry. The octahedral Zn(Ⅱ) nodes and L linkages build up 2-D nets consisting of parallelogram-like grids in the ab plane. The neighboring nets stack through hydrogen bonds to generate 3-D rhombic channels. In 1, the 1,4-dioxane and MeOH guests alternatively arrange in the channels and effectively take up the free space; while in 2, the CH2Cl2 guests are arranged in the channels. In addition, the encapsulated MeOH molecules are bonded to the framework by hydrogen bonds.     

手性pybox-金属络合物及其在不对称催化反应中的应用

具有C2对称性的双噁唑啉型吡啶(pybox)是一类有效的手性配体,能与许多金属离子配位,其手性催化性能已得到越来越多的关注。本文综述了手性配体pybox和pybox-金属络合物的合成方法,特别是近年来pybox-金属络合物在不对称催化反应如不对称环丙烷化反应、不对称Diels-Alder反应、1,3-偶极环加成反应、不对称aldol反应等中应用的最新进展。