Synthesis of chiral allenes from ynamides through a highly stereoselective Saucy-Marbet rearrangement

A highly stereoselective Saucy-Marbet rearrangement using chiral ynamides and propargyl alcohols is described here. This rearrangement can be catalyzed by para-nitrobenzenesulfonic acid and leads to high diastereoselectivities for a range of different chiral propargyl alcohols and ynamides in a stereochemically intriguing matched, mismatched or indifferent manner. The stereoselective Saucy-Marbet rearrangement of ynamides provides an excellent entry to highly substituted chiral homo allenyl alcohols.     

Synthesis of chiral ortho-thio-substituted phenyl phosphonodiamidates via a P-S to P-C rearrangement

The ortho-lithiation of a phenyl phosphorodiamidothioate derived from an enantiopure C₂-symmetric diamine is studied. It is shown that the migration of the diaminophosphoryl group from sulfur to carbon, leading to an ortho-sulfanylated phenyl phosphonodiamidate, only occurs in the presence of an alkylating agent or a Lewis acid as BF₃·Et₂O. The influence of the chiral diaminophosphoryl group on the stereoselectivity of the oxidation of the ortho-sulfanyl or alkylsulfanyl group is also examined.     

Highly stereoselective Saucy-Marbet rearrangement using chiral ynamides. Synthesis of highly substituted chiral homoallenyl alcohols

[reaction: see text] A highly stereoselective Saucy-Marbet rearrangement using chiral ynamides and propargyl alcohols is described here. This rearrangement can be catalyzed by para-nitrobenzenesulfonic acid leading to high diastereoselectivities for a range of different chiral propargyl alcohols and ynamides in a stereochemically intriguing matched, mismatched, or indifferent manner. This provides an excellent entry to highly substituted chiral homoallenyl alcohols.     

Synthesis of chiral [5]helicenes using aromatic oxy-Cope rearrangement as a key step

Both enantiomers of (P)-(+)-2- and (M)-(−)-2-acetoxy-11,14-dimethyl[5]helicenes 8 were synthesized by asymmetric aromatic oxy-Cope rearrangement of the corresponding chiral bridged bicyclic compounds, which were obtained by enzymatic resolution. The absolute configurations of 8 were assigned by their circular dichroism spectra.     

Synthesis of diterpene glycosides

Summary Mono-, di-, and linear triglycosides of a diterpene alcohol, derived from abietic acid and glucose have been synthesized employing peracetylbromo--D-glucose (4) and maltose derivatives5 and8 as glycosyl donors. The triglycoside14 exhibits slight haemolytic activity.

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Synthese von Diterpenglycosiden

Zusammenfassung Es wird die Synthese von Mono-, Di-, und linearen Triglycosiden aus einem von Abietinsäure abgeleiteten Diterpenalkohol beschrieben. Als Glycosyldonoren wurden neben Peracetobrom--D-glucose (4) die Maltosederivate5 und8 verwendet. Das Triglycosid14 zeigt schwache hämolytische Aktivität.

     

Engineering of chiral nanomaterials for biomimetic catalysis

Chiral nanomaterial-based biomimetic catalysts can trigger a similar biological effect to natural catalysts and exhibit high performance in biological applications. Especially, their active center similarity and substrate selectivity promoted their superior biocatalytic activity. Here, modification of critical elements, such as size, morphology, nanocrystal facets, chiral surface and active sites, for controlling the catalytic efficiency of individual chiral nanoparticles (NPs) and chiral nanoassemblies has been demonstrated, which had a synergistic effect on overcoming the defects of pre-existing nanocatalysts. Noticeably, application of external forces (light or magnetism) has resulted in obvious enhancement in biocatalytic efficiency. Chiral nanomaterials served as preferable biomimetic nanocatalysts due to their special structural configuration and chemical constitution advantages. Furthermore, the current challenges and future research directions of the preparation of high-performance bioinspired chiral nanomaterials for biological applications are discussed.

Chiral nanomaterial-based biomimetic catalysts can trigger a similar biological effect to natural catalysts and exhibit high performance in biological applications.     

Synthesis of ent-kaurane diterpene monoglycosides

Synthesis of two ent-kaurane diterpene glycosides, steviol 19-O-β-D-glucopyranosiduronic acid (steviol glucuronide, 5), and 13-hydroxy ent-kaur-16-en-19-oic acid-β-D-glucopyranosyl ester (7) has been achieved from a common starting material, steviol, using phase transfer catalyst. Also, synthesis of an additional 17-nor-ent-kaurane glycoside, namely 13-methyl-16-oxo-17-nor-ent-kauran-19-oic acid-β-D-glucopyranosyl ester (10) was performed using the starting material isosteviol and similar synthetic methodology. Synthesis of all three steviol glycosides was performed using straightforward chemistry and their structures were characterized on the basis of 1D and 2D NMR as well as mass spectral (MS) data.     

Enantioselective rearrangement of a meso-cyclohexene oxide using norephedrine-derived chiral bases

Using a chiral base from a norephedrine-derived diamine, the enantioselective rearrangement of a meso-cyclohexene oxide can be performed in 94% yield and with 94% enantioselectivity. The enantioselectivity is lower (86% ee) with the diastereoisomeric chiral base. In order to prepare the diastereoisomeric chiral base, a potentially useful way of converting norephedrine into norpseudoephedrine was developed.     

Self-sorting chiral subcomponent rearrangement during crystallization

The incorporation of enantiopure 1-amino-2,3-propanediol as a subcomponent into a dicopper double helicate resulted in perfect chiral induction of the helicate's twist. DFT calculations allowed the determination of the helicity of the complex in solution. The same helical induction, in which S amines induced a Lambda helical twist, was observed in the solid state by X-ray crystallography. Electronic structure calculations also revealed that the unusual deep green color of this class of complexes was due to a metal-to-ligand charge transfer excitation, in which the excited state possesses a valence delocalized Cu2(3+) core. The use of a racemic amine subcomponent resulted in the formation of a dynamic library of six diastereomeric pairs of enantiomers. Surprisingly, this library converted into a single pair of enantiomers during crystallization. We were able to observe this process reverse upon redissolution, as initial ligand exchange was followed by covalent imine metathesis.     

Synthesis and application of a chiral diborate

A chiral diborate with different counterions is reported whose structure was unambiguously confirmed by X-ray analysis. This chiral dianion was used in the resolution of trans-1,2-diamines and also as a chiral shift reagent for NMR analysis of triphenylphosphonium salts.     

Synthesis of a caryophyllene isoprenologue, a potential diterpene natural product

(−)-β-Caryophyllene has been converted into three stereoisomers of a new bicyclic compound that is structurally related to the known macrocyclic diterpene, flexibilene, in the same way β-caryophyllene is related to humulene. Key steps are selective cleavage of caryophyllene, addition of a five carbon component by a Wittig reaction and McMurry cyclization.     

Synthesis of flexibilene,a naturally occurrring 15-membered-ring diterpene

A total synthesis of the naturally occurring 15-membered ring diterpene, flexibilene, was accomplished using a titanium-induced cyclization of the keto-aldehyde 3,37,11-tetramethyl- 15-oxohexadeca-4E,7E,11E-trienal as the key step.     

Synthesis of biomimetic heme precursors

Three kinds of biomimetic heme precursors have been prepared. The first type is based on tetra-aminoporphyrins: either 5,10,15,20-tetrakis (o-aminophenyl)porphyrin (various atropoisomers), or 5,15-bis(2′,6′-diaminophenyl)porphyrin. The second type is based on octa-aminoporphyrins: 5,10,15,20-tetrakis (2′,6′-diamino-4′-tert-butylphenyl)porphyrin. One example of “basket handle” porphyrin demonstrates selective discrimination between O₂ and CO with an M value [M=p_1/2(O₂)/p_1/2(CO)] of 105. This is similar to values reported for various natural hemoproteins. The third type is based on aminoporphyrin templates [5, 5,10- or 5,15- and 5,10,15-(2′,6′-dinitro,4′-tert-butylphenyl)porphyrins] which have been tested in asymmetric epoxidation.     

The stereoselective thermal rearrangement of chiral lophine peroxides

The thermal reaction of chiral 2-phenyl-4-(p-X-phenyl)-5-(p-Y-phenyl)-4-tert-butyldimethylsilylperoxy-4H-isoimidazoles (5b: X = CF₃, Y = OMe; 5c: X = CF₃, Y = F) was carried out in DMSO. The chiral 2-phenyl-5-(p-X-phenyl)-5-(p-Y-phenyl)-5H-imidazol-4-ones (4b: X = CF₃, Y = OMe; 4c: X = CF₃, Y = F) were quantitatively obtained in 50-60% enantiomer excess (ee). The mechanism for the reaction was proved to be stereoselective 1,5-phenyl migration. Although the sigmatropic 1,5-phenyl migration should be thermally allowed according to the Woodward-Hoffmann rule, the migration actually includes a stepwise process.     

Synthesis and rearrangement of triazinoquinazolines

Selective syntheses of triazino[4,3-a]quinazolines 3a–e and their isomeric triazino[3,2-b]quinazolines 4a–e by cyclization of the appropriate α -keto acid hydrazones 2a–e under different reaction conditions are described. The angular triazinoquinazolines 3a–e were readily rearranged to the corresponding linear isomers 4a–e when heated in acetic anhydride in the presence of sodium acetate. This rearrangement was proposed to proceed via the intermediate isomeric triazino[3,4-b]quinazolines 5a–e . The N-methyl derivative 10 (of the intermediate 5b ) was prepared and rearranged to 11 , which is the N-methyl derivative of 4b .     

一种含三嗪单元多齿手性配体的合成

以（R,R）-1,2-二苯基乙二醇和氰尿酰氯为原料,经保护、醚化、去保护、取代等反应合成了一种新的手性多齿配体2-乙氧基-4-（2-甲氧基-乙氧基）-6-(（1R,2R）-1,2-二苯基-2-甲氧基-乙氧基)-1,3,5-三嗪,并通过1HNMR 、LCMS和元素分析对目标化合物的结构进行了表征。     

Synthesis of a chiral hexa-host molecule

The synthesis of the first chiral hexa-host molecule (III) is described: an X-ray analysis of the acetic acid adduct of (III) allows the first direct observation of dimeric acetic acid.     

Asymmetric Carroll rearrangement of allyl alpha-acetamido-beta-ketocarboxylates catalysed by a chiral palladium complex

Asymmetric decarboxylative rearrangement (Carroll rearrangement) of allyl alpha-acetamido-beta-ketocarboxylates was catalysed by a palladium complex modified with a chiral phosphine ligand, giving optically active gamma,delta-unsaturated alpha-aminoketones with up to 90% ee.