Synthesis of Planar Chiral Carbazole Derivatives Bearing a [2.2]Paracyclophane Skeleton

The synthesis of planar chiral carbazoles bearing a [2.2]paracyclophane backbone is described. Starting from readily available 4-bromo[2.2]paracyclophane planar chiral carbazoles are obtained in a two-step synthesis by Pd-catalyzed C N cross-coupling and subsequent oxidative cyclization.     

A new planar chiral bipyridine-ligand: pyrid-2-yl[2](1,4)benzeno[2](5,8)quinolino-phane

The synthesis of the new planar chiral heterocyclic nitrogen ligand pyrid-2-yl[2](1,4)benzeno[2](5,8)quinolino-phane ( 1 with [2.2]paracyclophane-skeleton is described. The enantiomeric resolution is achieved by HPLC. The CD-spectra of 1 and of its chiral quinoline precursor are recorded. The enantiomerically pure title compound 1 is used in copper-catalyzed asymmetric cyclopropanation of styrene and in asymmetric iridium-catalyzed transfer-hydrogenation of acetophenone.     

Palladium‐Catalyzed C?H Bond Acetoxylation: An Approach to ortho‐Substituted Hydroxy[2.2]paracyclophane Derivatives

The palladium‐catalyzed direct C H bond acetoxylation of [2.2]paracyclophanes has been investigated. Various mono‐ and disubstituted [2.2]paracyclophanes were subjected to typical Sanford acetoxylation conditions. Oxime ethers, an oxime acetate, a pyridine, and a pyrazole with [2.2]paracyclophane cores underwent direct ortho‐acetoxylation in good to excellent yields using 1–5 mol% of palladium(II) acetate in combination with iodobenzene diacetate as oxidant. The reactions could be performed on a multigram scale, and the ortho‐acetoxylated [2.2]paracyclophanes were suitable for further functionalizations affording a hydroxy[2.2]paracyclophane derivative and a planar chiral benzoxazole.     

Highly Stereoselective Synthesis of Novel Multistereogenic Bis‐Bifunctional Ligands Based on [2.2]Paracyclophane‐ 4,7‐quinone,their Structure Elucidation and Application in Asymmetric Catalysis

Bis‐bifunctional cis‐4,7‐diarylsubstituted‐4,7‐dihydroxy‐4,7‐dihydro[2.2]paracyclophanes 3–6 were synthesized by a highly diastereoselective reaction of ortho‐substituted aryllithium reagents with [2.2]paracyclophane‐4,7‐quinone ( 1 ). Enantiomerically pure diols 3–5 were tested as chiral inductors in the enantioselective addition of diethylzinc to benzaldehyde (up to 93.5% ee). Acid dehydration of cis‐4,7‐di(2‐methoxyphenyl)‐4,7‐dihydroxy‐4,7‐dihydro[2.2]paracyclophane ( 3 ) results in 4,7‐dihydro‐7,8‐di(2‐methoxyphenyl)[2.2]paracyclophane‐4‐one ( 8 ) – a planar chiral cyclohexadienone of the [2.2]paracyclophane series with a para‐semiquinoid substructure. X‐Ray investigations of compounds 3, 4 and 8 were performed.     

[2.2]Paracyclophane as a Target of the Organic Solid State: Emergent Properties via Supramolecular Construction

In this account, we review the synthesis of [2.2]paracyclophanes in the organic solid state. Reactions in crystalline solids provide a means to obtain molecules with high degrees of stereocontrol that can also be unattainable in solution. We show that [2.2]paracyclophanes form in the solid state stereospecifically and in quantitative yield via intermolecular [2+2] double photodimerization reactions. The double cycloaddition that affords a paracyclophane in the solid state does not readily occur in solution. Small molecules in the form of hydrogen-bond-donor templates can provide access to [2.2]paracyclophanes in a solid by design. A [2.2]paracyclophane obtained using a hydrogen-bond template is shown to exhibit attractive optical properties and has been employed as a building block of a metal-organic framework (MOF).     

Second‐Generation Paracyclophane Imine Ligands for the Dialkylzinc Addition to Aldehydes. Optimization of the Branched Side Chain leads to Improvement for Aliphatic Aldehydes

Two novel diastereomeric [2.2]paracyclophane ketimine ligands (S_P,S)‐ 2 and (R_P,S)‐ 2 , which unite a planar chiral element and a central chiral element, were used towards the enantioselective diethylzinc addition onto aliphatic aldehydes. These improved second‐generation ligands, which are stable in air and water and are easy to obtain, showed significant improvements with respect to the ligands that were previously used.     

Inherently chiral calixarenes: synthesis, optical resolution, chiral recognition and asymmetric catalysis

Inherently chiral calixarenes, whose chirality is based on the absence of a planar symmetry or an inversion center in the molecules as a whole through the asymmetric array of several achiral groups upon the three-dimensional calix-skeletons, are challenging and attractive chiral molecules, because of their potential in supramolecular chemistry. The synthesis and optical resolution of all varieties of inherently chiral calixarenes are systematically discussed and classified, and their applications in chiral recognition and asymmetric catalysis are thoroughly illustrated in this review.     

Aryl[2.2]paracyclophane-Based Chiral Regioisomeric Analogs of Salicyl Aldehyde: Novel Sources for Construction of Phenoxy-Imine Ligands

The efficient, high-yield approaches to two novel regioisomeric salicyl aldehyde analogs, 4-formyl-13-(2-hydroxyphenyl)-[2.2]paracyclophane and 4-formyl-12-(2-hydroxyphenyl)-[2.2]paracyclophane ( iso -FHPhPC and pseudo -FHPhPC , respectively), constructed on the basis of an aryl[2.2]paracyclophane backbone are described. The key stage of the backbone formation is the Suzuki cross-coupling of paracyclophanyl halides with arylboronic acids. Efficient procedures for the resolution of the racemic hydroxy aldehydes into enantiomers via Schiff bases with enantiomers of α-phenylethyl amine were elaborated, and the absolute configurations of enantiomers were established on the basis of X-ray analysis of diastereomeric imines. Starting from these chiral hydroxy aldehydes the first representatives of bi-, tri-, and tetradentate phenoxy-imine ligands belonging to an aryl[2.2]paracyclophane family were obtained. The induction power of the ligands was tested in the Et₂Zn asymmetric addition to aldehydes.     

Enantioselective Synthesis of Highly Functionalized Trifluoromethyl‐Bearing Cyclopentenes: Asymmetric [3+2] Annulation of Morita–Baylis–Hillman Carbonates with Trifluoroethylidenemalonates Catalyzed by Multifunctional Thiourea‐Phosphines

On the basis of the design and synthesis of multifunctional thiourea‐phosphines, a catalytic method for the asymmetric [3+2] annulation of Morita–Baylis–Hillman carbonates with trifluoroethylidenemalonates has been developed, affording highly functionalized trifluoromethyl‐bearing cyclopentenes in excellent yields, high diastereoselectivities and enantioselectivities under mild conditions.     

Cyclometalated N‐Heterocyclic Carbene‐Platinum Catalysts for the Enantioselective Cycloisomerization of Nitrogen‐Tethered 1,6‐Enynes

Platinum(II) complexes which combine six‐membered N‐heterocyclic carbene‐containing metallacyclic units and monodentate chiral phosphines have been prepared. The key step of their synthesis is the intramolecular oxidative addition of N‐2‐iodobenzylimidazolylidene‐platinum(0)‐diene complexes in the presence of the chiral phosphorus ligands. The platinum(II) metallacycles have been used as well‐defined pre‐catalysts for the enantioselective cycloisomerization of nitrogen‐tethered 1,6‐enynes into 3‐azabicyclo[4.1.0]hept‐4‐enes. High enantiomeric excesses have been obtained with either Monophos or phenyl‐Binepine based catalysts (ees=82–96%), although phenyl‐Binepine outperforms Monophos in these reactions. The absolute configuration of the final 3‐azabicyclo[4.1.0.]heptenes has been established by X‐ray diffraction studies. The method has been extended then to the cycloisomerization of dienynes with enantiotopic vinyl groups. An (S)‐phenyl‐Binepine‐platinum(II) complex allows total diastereoselectivity and high enantioselectivity levels to be attained in these reactions (ees up to 95%) which represent the first enantioselective desymetrizations achieved via enyne cycloisomerizations.     

Chiral Polymers and Polymeric Particles for Enantioselective Crystallization

Chiral polymers and chiral polymeric particles have emerged as a new and exciting field of research in recent years mainly due to their possibly applications in chiral chemistry. This paper reviews the present state of the art regarding production techniques for the synthesis and applications of chiral polymeric particles. The main methods for preparing of chiral polymeric particles such as: direct polymerization, emulsion, precipitation, and suspension polymerization of chiral monomers, are reviewed. Moreover, in this article we also present the use of chiral polymers as chiral templates for the synthesis of chiral mesoporous materials. In this review we highlighted the properties and parameters involved in the preparation of these chiral polymeric materials. The present review focuses mainly on the use of chiral polymer and chiral polymeric particles for enantioselective crystallization and enantioseparation. References of the most relevant literature published by various research groups are provided. Anyway, it is clear that chiral polymeric particles are a distinctive type of chiral nanomaterials that can find many new application in other fields like, chiral drug delivery systems, enantioselective catalysis. We hope that this review article will inspired new researchers in this field and will boost the research dealing on chiral polymeric particles especially in their implementation in new areas in chiral chemistry.     

[2.2]Paracyclophane-Derived Planar-Chiral Hydrogen-Bond Receptors

The development of planar-chiral hydrogen-bond donors based on the [2.2]paracyclophane scaffold is discussed. General strategies to access functionalized enantiopure [2.2]paracyclophane derivatives are briefly reviewed, with the focus on suitable precursors for the synthesis of planar-chiral thiourea derivatives. The synthesis of fourteen hydrogen-bond donors is described. The interaction of four thiourea derivatives with hydrogen-bond acceptors (DMSO and tetramethylammonium chloride) was investigated by ¹H NMR spectroscopy and X-ray crystallography. A selection of enantiomerically pure planar-chiral derivatives was applied in asymmetric hydrogen-bond catalysis.     

Cyclophanes,XXIII [1] [2.2] Indenophanes — Building Blocks for Novel Multilayered Organoiron Complexes

A general approach for the synthesis of [2.2] indenophanes is described employing readily available mono-(8, 13) and bis-formyl[2.2]paracyclophanes (20, 21) as substrates. The anellated five-membered ring is introduced by a multistep sequence involving Wittig-Horner chain elongation of the different aldehydes, saponification, catalytic hydrogenation, acid-catalyzed ring closure, and dehydration. In this manner the novel indenophanes 11, 16, 17, 26, and 27 have been synthesized in good yields. The first representatives of a novel class of extended metallophanes, the multilayered ferrocenophanes 32 and 34, have been prepared from 11 and 28, respectively, via their sodium salts 29 and 33. The effect of an anellated [2.2] paracyclophane unit on the proton chemical shifts of the model compounds 30, 31, and 35 is discussed.     

Enantioselective nucleophilic catalysis with "Planar-Chiral" heterocycles

Although Lewis bases (e.g., tertiary phosphines, tertiary amines, and pyridines) serve as nucleophilic catalysts for a wide array of reactions, there have been relatively few reports of enantioselective nucleophilic catalysts. In this Account, we describe the design and synthesis of a new family of chiral nucleophilic catalysts, specifically, planar-chiral heterocycles. These complexes provide good levels of enantiomeric excess in the addition of alcohols to ketenes, the rearrangement of O-acylated azlactones, and the kinetic resolution of secondary alcohols.     

Structures of gold(i) and silver(i) thiolate complexes of medicinal interest: a review and recent results

We review the crystal structures, electrospray ionization mass spectra (ESI-MS) data and chiral HPLC data for the racemic and optically pure mononuclear AuL2 complexes, and for racemic [AuLI]n and optically pure [AgLII]n polymers (LI = thiomalate, LII = D-penicillamine). We postulate an equilibrium between polymeric, mononuclear and free ligand species for [AuLII]n (gold sodium thiomalate or GST). The ESI-MS results clearly show a tetrameric principal species in the 1:1 gold polymers, [AuLI]n. For the 1:1 silver: D-penicillamine complex, [AgLII]n, a non-molecular crystal of double helical structure, the ESI-MS results show multi-ligand-silver species, including tetramers, pentamers and hexamers. Other, relevant gold, silver and copper complexes are compared.     

Biocatalytic synthesis of some chiral pharmaceutical intermediates by lipases

Chiral intermediates were prepared by biocatalytic processes for the chemical synthesis of three pharmaceutical drug candidates. These include (i) the synthesis of [(3R-cis)-3-(acetyloxy)-4-phenyl-2-azetidinone2 for the semi-synthesis of paclitaxel (taxol)5, an anticancer compound; (ii) synthesis of chiral (exo,exo)-7-oxabicyclo [2.2.1] heptane-2,3-dimenthanol monoacetate ester9 for the chemoenzymatic preparation of a thromboxane A₂ antagonist; (iii) the enzymatic synthesis ofS-(−) 3-benzylthio-2-methylpropanoic acid, a key chiral intermediate for the synthesis of antihypertensive drugs captopril10 or zofenopril13.     

Application of Lawesson’s reagent in the synthesis of sulfur-containing medicinally significant natural alkaloids

This review aims to illustrate the applications of Lawesson's reagent (LR) [2,4-bis(p-methoxyphenyl)-1,3,2,4-dithiadiphosphetane-2,4-disulfide] in the synthesis of naturally occurring medicinally important alkaloids. LR is primarily used for thionation; it is a versatile reagent employed for diverse transformations (cyclizations, rearrangements, and synthesis of heterocyclic compounds). The medicinal importance of alkaloids has also been concisely highlighted. The main focus of the review is the use of LR in the synthesis of natural alkaloids and only the thionation steps involved have been highlighted.     

Amphiphilic phosphines for catalysis in the aqueous phase

Two new phosphines, Tris[p-(10-phenyldecyl)phenyl]phosphine and 2,2′-Bis{di[p-(10-phenyldecyl)phenylphosphinomethyl}-1,1′-biphenyl were successfully synthesized and sulfonated in concentrated H₂SO₄. The resulting water soluble surface active phosphines were applied to the rhodium catalyzed hydroformylation of higher olefins. It is found that these two ligands are not only excellent for octene hydroformylation, but catalyze tetradecene hydroformylation under two phase conditions as well. Rates and selectivities are superior to TPPTS modified rhodium catalysts under the same reaction conditions.     

Combining in situ Generated Chiral Silicon Lewis Acid and Chiral Brønsted Acid Catalysts for [3+2] Cycloadditions: Cooperative Catalysis as a Convenient Enantioselective Route to Pyrazolidines

A facile enantioselective synthesis of chiral pyrazolidines via a [3+2] cycloaddition reaction, involving a BINOL‐derived phosphoric acid and an in situ generated BINOL phosphate‐derived silicon Lewis acid, which may act cooperatively, has been developed.     

Amorphous silicon nanocone array solar cell

ABSTRACT: In the hydrogenated amorphous silicon [a-Si:H]-thin film solar cell, large amounts of traps reduce the carrier's lifetime that limit the photovoltaic performance, especially the power conversion efficiency. The nanowire structure is proposed to solve the low efficiency problem. In this work, we propose an amorphous silicon [a-Si]-solar cell with a nanocone array structure were implemented by reactive-ion etching through a polystyrene nanosphere template. The amorphous-Si nanocone exhibits absorption coefficient around 5 × 105/cm which is similar to the planar a-Si:H layer in our study. The nanostructure could provide the efficient carrier collection. Owing to the better carrier collection efficiency, efficiency of a-Si solar cell was increased from 1.43% to 1.77% by adding the nanocone structure which has 24% enhancement. Further passivation of the a-Si:H surface by hydrogen plasma treatment and an additional 10-nm intrinsic-a-Si:H layer, the efficiency could further increase to 2.2%, which is 54% enhanced as compared to the planar solar cell. The input-photon-to-current conversion efficiency spectrum indicates the efficient carrier collection from 300 to 800 nm of incident light.