Enantioselective organocatalytic indole alkylations. Design of a new and highly effective chiral amine for iminium catalysis

The indole framework has become widely identified as a "privileged" structure with representation in over 3000 natural isolates and 40 medicinal agents of diverse therapeutic action. A new strategy for asymmetric access to this important pharmacaphore has been accomplished that involves the amine catalyzed alkylation of indoles with alpha,beta-unsaturated aldehydes. Central to these studies has been the design of a new chiral amine catalyst that exhibits improved reactivity and selectivity for iminium catalysis. This new (2S,5S)-5-benzyl-2-tert-butyl-imidazolidinone catalyst has enabled the conjugate addition of a variety of indole systems to a diverse range of alpha,beta-unsaturated aldehydes in high yield and with excellent levels of enantiocontrol (70-97% yield, 84-97% ee). A demonstration of the utility of this new organocatalytic alkylation for the rapid construction of biomedically relevant molecules is presented in the enantioselective synthesis of an indolobutyric acid COX-2 inhibitor.     

Enantioselective organocatalytic Michael-hemiketalization catalyzed by a trans-bifunctional indane thiourea catalyst

An efficient, convenient and enantioselective Michael-hemiketalization reaction has been developed for the synthesis of naphthoquinones. In this work, a novel trans-bifunctional indane thiourea catalyst has been reported to promote this process to afford high yields (up to 99%) and high to excellent enantiomeric excesses (90-98% ee).     

Enantioselective organocatalytic intramolecular Diels-Alder reactions. The asymmetric synthesis of solanapyrone D

The first direct enantioselective organocatalytic intramolecular Diels-Alder reaction has been accomplished. The use of iminium catalysis has provided a new catalytic strategy for the enantioselective [4 + 2] cycloisomerization of a wide variety of tethered diene-enal systems. The use of imidazolidinones 1 and 2 as the asymmetric catalysts has been found to mediate the enantioselective construction of [4.4.0] and [4.3.0] ring systems. Application of this methodology to the highly efficient asymmetric synthesis of the marine metabolite solanpyrone D has also been accomplished. A diverse spectrum of aldehyde substrates can also be accommodated in this new organocatalytic transformation. Importantly, this technology has been utilized to execute the first enantioselective, catalytic Type II IMDA reaction.     

Enantioselective organocatalytic aldehyde-aldehyde cross-aldol couplings. The broad utility of α-thioacetal aldehydes

An asymmetric proline catalyzed aldol reaction with α-thioacetal aldehydes has been developed. Thioacetal bearing aldehydes readily participate as electrophilic cross-aldol partners with a broad range of aldehyde and ketone donors. High levels of reaction efficiency as well as diastereo- and enantiocontrol are observed in the production of anti-aldol adducts.     

Enantioselective total synthesis of the pumiliotoxin a alkaloids via reductive iminium ion-alkyne cyclizations. Total synthesis of (+)-pumiliotoxin a

A highly practical new route for the enantioselective synthesis of the pumiliotoxin A alkaloids in which the title reaction is a key step is disclosed.     

Enantioselective addition of diethylzinc to aldehydes induced by a new chiral Ti(IV) catalyst

A new chiral titanium reagent, derived from optically active trans-1,2-dicamphorsulfonamidocyclohexane 2a and Ti(OⁱPr)₄, was found to promote the enantioselective addition of diethylzinc to various aldehydes giving rise to the corresponding alcohols in high yields with moderate to high selectivity.     

Hodgsonox, a new class of sesquiterpene from the liverwort Lepidolaena hodgsoniae. Isolation directed by insecticidal activity

Hodgsonox (1), a new insecticidal sesquiterpene, has been isolated from the New Zealand liverwort Lepidolaena hodgsoniae. The structure was elucidated on the basis of 2D NMR analysis of 1 and a synthetic epoxide derivative (2). Hodgsonox represents a new class of sesquiterpene with a cyclopenta[5,1-c]pyran ring system fused to an oxirane ring. The combination of a mono- and a 1,1 disubstituted double bond flanking the oxygenated carbon of a the pyran ring is a unique structural feature. Hodgsonox is toxic to larvae of the blowfly Lucilia cuprina.     

Complex triarylsulfonium salt photoinitiators. I. The identification,characterization, and syntheses of a new class of triarylsulfonium salt photoinitiators

Dilphenyl-4-thiophenoxyphenylsulfonium salts have been found to be more efficient cationic photoinitiators than the highly photoactive triphenylsulfonium salts. The former compounds were identified as by-products produced in the preparation of triphenylsulfonium chloride from benzene, chlorine, sulfur monochloride, and aluminum chloride. Confirmation of the structure was made by NMR and UV spectroscopy as well as by independent synthesis. The photoinitiated cationic polymerization of cyclohexene oxide and other epoxy monomers was carried out to demonstrate the higher efficiency of diphenyl-4-thiophenoxysulfonium hexafluoroarsenate as compared to the corresponding triphenylsulfonium salt.     

Enantioselective fluorescent recognition of a soluble "supported" chiral acid: toward a new method for chiral catalyst screening

The long-chain aliphatic-group-substituted mandelic acid 3c, which is soluble only in THF and insoluble in water and many polar/nonpolar organic solvents, has been synthesized. This unique solubility allows 3c to be easily isolated from reaction mixtures and makes it potentially useful for catalyst screening. The fluorescent sensors (R)- and (S)-1 can be used to determine the ees of various samples of 3c generated from a series of catalyst screening experiments. The fluorescence measurements correlate well with the conventional HPLC-chiral column analysis. This work demonstrates that the enantioselective fluorescent recognition of organic substrates can lead to a fundamentally new method for chiral catalyst screening. [reaction: see text]     

Enantioselective Pd-catalyzed allylic alkylation of indoles by a new class of chiral ferrocenyl P/S ligands

Chiral ferrocenyl heterobidentate P/S ligands bearing both central and planar chirality were prepared from (S)-Ugi's amine via a three-step modular synthesis. Through systematic screening and optimization, L8 was found to be the best ligand for Pd-catalyzed asymmetric allylic alkylation of indoles with ee's up to 96% being attained.     

High-speed living ring-opening polymerization by a new catalyst based on metalloporphyrin

Polymerization of ϵ-caprolactone and δ-valerolactone initiated with aluminum porphyrin (1) was much accelerated by the addition of methylaluminum diphenoxide with bulky substituents 2, to give polymers with narrow molecular weight distribution. The polymerization of β-butyrolactone was also accelerated by 2, to different extents depending on the mode of ring scission. 2 also accelerated the living polymerization of propylene sulfide initiated with zinc porphyrin (3). The effect of 2 is due to the coordinative activation of monomer.     

Synthesis of a new nanoparticle system based on electrostatic alginate‐piperazine interactions

Advanced drug delivery system development is very important for the cancer therapies. The fixing of specific targeting ligands onto biodegradable carriers can add specificity to the usual chemotherapeutical treatments that current chemotherapies lack of. This study describes the preparation of a new nanoparticle system based on electrostatic interactions between alginate and piperazine. Nanoparticles with a negative surface charge were prepared through the electrostatic interaction between alginate and piperazine under acid aqueous condition. This kind of interactions and materials has never been used before to produce nanoparticles. This nanoparticle system has been designed to be used as a carrier where superficial carboxylate groups are the binding site for different kind of molecules, for example, proteins and organic molecules. Afterwards, surface engineering was performed on the nanoparticles produced; cisplatin and epidermal growth factor (EGF) were covalently linked on the surface of the nanoparticle using reagents by carbodiimide chemistry to give a covalent bond between EGF and nanoparticles and between cisplatin and nanoparticles. As a result, this study reports the development of a potential advanced drug delivery system, which in the future will enable clinical trials in animals and humans. Copyright © 2015 John Wiley & Sons, Ltd.     

Palladium hydrogenation catalyst based on a porous carbon material obtained upon the dehydrochlorination of a chloro polymer

The applicability of a porous carbon material obtained as a result of the “chemical” dehydrochlorination of chlorinated polyvinyl chloride as a support for palladium hydrogenation catalysts was demonstrated. The efficiency of the catalyst was evaluated in the liquid-phase reactions of nitrobenzene hydrogenation and chlorobenzene hydrodechlorination. Although the specific activity of the catalyst was lower by a factor of 3–4 than that of the samples based on Sibunit and carbon nanotubes, the complete conversion of the initial compounds with the selective formation of end products under mild conditions was achieved at a relatively low palladium content (1.5%).     

Asymmetric catalysis LVI. Enantioselective hydrosilylation of acetophenone with a rhodium/picolineoxazoline catalyst 1:1

The direction of optical induction is inverted in going from pyridineoxazoline 1 to picolineoxazoline 2 as cocatalyst in the Rh-catalyzed asymmetric hydrosilylation of acetophenone with diphenylsilane. In the case of ligand 2, a 1.2-fold excess of the ligand is sufficient to achieve the highest enantiomeric excess.     

Cationic zinc complexes: a new class of catalyst for living lactide polymerization at ambient temperature

Cationic zinc complexes of a bis(phosphinimine) pincer ligand have been prepared. Methylzinc and zinc-lactate complexes have been structurally characterized, and the latter is the first cationic metal complex to promote coordination-insertion polymerization of lactide at ambient temperature. This novel catalyst system is remarkably active and also exhibits living character. A detailed investigation of the kinetics and mechanism of the polymerization process has been undertaken.     

The synthesis and characterization of a new class of liquid crystalline polymers based on s-triazine

Abstract

The synthesis and characterization of a new class of liquid crystalline alternating copolymers based on s-triazine rings, connected by flexible alkyldiamine spacers and other selected bridging groups is reported. The propensity of the system to demonstrate liquid crystallinity as a function of the bridging group is investigated. Unexpectedly, the homopolymer of the triazine ring connected by a flexible alkyldiamine spacer is also a liquid crystalline polymer. A new polymerization technique is reported in which the alkyldiamine serves the dual role of monomer and proton acceptor. These polymers form liquid crystalline glasses which are transparent and have good mechanical properties. This suggests that they could be interesting materials to be further studied in the context of non-linear optics.     

The synthesis and characterization of a new class of liquid crystalline polymers based on s-triazine

The synthesis and characterization of a new class of liquid crystalline alternating copolymers based on s-triazine rings, connected by flexible alkyldiamine spacers and other selected bridging groups is reported. The propensity of the system to demonstrate liquid crystallinity as a function of the bridging group is investigated. Unexpectedly, the homopolymer of the triazine ring connected by a flexible alkyldiamine spacer is also a liquid crystalline polymer. A new polymerization technique is reported in which the alkyldiamine serves the dual role of monomer and proton acceptor. These polymers form liquid crystalline glasses which are transparent and have good mechanical properties. This suggests that they could be interesting materials to be further studied in the context of non-linear optics.     

The quettamines: a new class of isoquinoline alkaloids

Three quettamine type alkaloids, which incorporate either a benzofuran or a dihydrobenzofuran moiety within the molecular framework, have been obtained from $\text{Berberis}$$\text{baluchistanica}$. These are dihydrosecoquettamine ($\text{1}$), secoquettamine ($\text{2}$), and quettamine chloride ($\text{3}$). Alkaloids $\text{1}$ and $\text{3}$ are racemates. Hofmann degradation of quettamine ($\text{3}$) provides secoquettamine ($\text{2}$) and the styrene $\text{4}$ which has a trans relationship between the hydrogens at C-1 and C-α, thus indicating the identical stereochemistry in quettamine. Emde reduction of quettamine leads to dihydrosecoquettamine ($\text{1}$) and the stilbene $\text{5}$. Two other polar alkaloids in the plant are (+)-armepavine methochloride ($\text{6}$) and oblongine chloride ($\text{7}$). An oblongine type alkaloid must be the biogenetic precursor for the quettamines. Arguments are presented favoring direct oxidative coupling in the biogenesis of the cularine alkaloids.