Synthesis and reactivity of enantiomerically pure N-alkyl-2-alkenyl azetidinium salts

A synthesis of stereodefined enantiomerically pure 2-alkenyl azetidines is described using Wittig olefination as key step. The quaternary triflate ammonium salts of these heterocycles were prepared in a stereoselective way and treatment of these azetidinium salts with a base (KHMDS or PhLi) induced a regioselective Stevens rearrangement leading to a 3-alkenyl pyrrolidine. An unprecedented S_N2′ reaction involving phenyllithium as nucleophile and an ammonium as leaving group was observed in one case.     

Crystal and molecular structure of 1-benzyl-1,2,2-trimethyl azetidinium bromide

The structure of the compound, 1-benzyl-1,2,2-trimethyl azetidinium bromide has been determined by a single crystal x-ray diffraction study. The compound crystallizes in the space group Pnam with four formula weights in a unit cell of dimensions a = 14.36, b = 13.73, c = 6.90₆ Å. The compound is partially disordered with the benzyl part ordered and the remainder of the ring disordered about the mirror plane. The azetidinium ring bears a close resemblance in bond distances, bond angles and conformation to the β-lactam ring found in penicillin. The disordering is discussed in detail and a comparison of the effects of fusing a second ring to the azetidinium moiety are explored. A final value of R = 0.09₄ for the 432 independent reflections was obtained.     

Facile low-temperature solid-state synthesis of efficient blue-emitting Cs3Cu2I5 powder phosphors for solid-state lighting

The discovery of new environmentally friendly luminescent materials with high photoluminescence quantum yield and long-term stability is critical for future solid-state lighting and displays applications. Although lead halide perovskite materials with excellent optical properties have been extensively investigated in recent years because they hold tremendous promise in optoelectronic devices, the toxicity of lead and poor air-stability still hinder their commercial applications. Moreover, while substantial work has been done on three-dimensional (3D) perovskite halides, the zero-dimensional (0D) halide emitters with bright luminescence remain elusive. Herein we report a facile solid-state reaction method to prepare an efficient lead-free all-inorganic halide material with 0D structure, Cs₃Cu₂I₅, with photoluminescence quantum yield up to 80%. Under ultraviolet excitation at 313 nm, the Cs₃Cu₂I₅ powder phosphors show a strong blue photoluminescence emission with peak at 445 nm and CIE color coordinates of (0.1486, 0.0873). Notably, Cs₃Cu₂I₅ exhibits good color stability at high temperatures and outstanding stability towards air exposure exceeding one month (30 days). These findings not only open up a door for the development of promising highly emissive low-dimensional halide materials for lighting and displays, but also offer a new scalable approach for the potential mass production of halide emitters.     

Preparation of enantiopure 2-acylazetidines and their reactions with chloroformates

Enantiopure 1-phenylethylazetidine-2-carboxylates and 2-acylazetidines were prepared and reacted with chloroformates to yield α-chloro-γ-amino butyric acid esters and ketones from ring opening reaction of azetidinium ion intermediate in a completely regio- and stereoselective manner.     

A Novel One‐Pot Conversion of Allyl Alcohols into Primary Allyl Halides Mediated by Acetyl Halide

A new and simple method for the synthesis of the primary allyl chlorides and bromides 9 – 16 from the secondary or tertiary allyl alcohols 3 – 8 and acyl halide was developed (Scheme 2, Table 1). Non‐commercially available secondary and tertiary allyl alcohols were synthesized from the related ketones and aldehydes via the addition of vinylmagnesium chloride. Mechanistic studies indicate that the alcohols were first acetylated by the acetyl halide and then protonated prior to substitution by the halide, Cl^? or Br^?, via an S_N2′ reaction, to yield the primary halides (Scheme 5).     

Dimethyl selenide complexes of copper,gallium and indium halides as potential precursors for selenium-containing chalcopyrite semiconducting materials

The coordination chemistry of copper, gallium and indium halides with the simplest possible selenoether i.e. Me₂Se was investigated with the aim to use the resulting complexes as precursors for selenium-containing chalcopyrite semiconducting materials. An optimized general procedure for the high yield synthesis is described and the influence of a halide ion on the structure and solubility of these metal halide dimethyl selenide complexes are discussed. These complexes were characterized by the elemental analysis, FT-IR and ¹H NMR spectroscopy as well as single crystal X-ray structures, the later study showing them to be monomeric for gallium halides, mono- or dimeric for indium halides and either an ion-pairs or 2-D extended structure in the case of copper halides.     

KI与无机铵盐催化CO2与环氧丙烷合成碳酸丙烯酯

以无毒、合成简单、廉价的无机铵盐(氨基甲酸铵、碳酸氢铵、碳酸铵等)为助催化剂, 研究其对卤化钾(KCl、KBr、KI)催化CO₂与环氧丙烷合成碳酸丙烯酯(PC)的影响. 结果表明, 卤化钾与无机铵盐显示出很好的协同催化效应. 其中以氨基甲酸铵为助催化剂, KI为主催化剂时, 催化合成PC的效果最好. 同时考察了催化剂用量、反应温度、CO₂初始压力、PC的预加入量、反应时间等因素对反应的影响. 在优化条件下, PC收率大于99%.     

Synthesis of Azocanes from Piperidines via an Azetidinium Intermediate

α-Trifluoromethyl azocanes are accessible from 2-(trifluoropropan-2-ol) piperidines by metal-free ring-expansion involving a bicyclic azetidinium intermediate. The opening of the azetidinium intermediate was achieved by various nucleophiles (amines, alcoholates, carboxylates, phosphonates, halides and pseudo-halides) with an excellent regio- diastereo- and enantioselectivity and in good yields. The relative configuration of the piperidines and azocanes were assigned and the deprotected azocanes offer opportunities for further derivatization.     

Ring expansion of azetidinium ylides: rapid access to the pyrrolizidine alkaloids turneforcidine and platynecine

[reaction: see text] Azetidinecarboxylate esters react readily with metallocarbenes in an inter- or intramolecular fashion to generate azetidinium ylides. Efficient [1,2]-shift by the ester-substituted carbon furnishes ring-expanded pyrrolidine products. In the case of substrate 1, this provides access to the pyrrolizidine alkaloids turneforcidine and platynecine via a high-yield, five-step sequence starting with readily available methyl 1-benzylazetidine-2-carboxylate.     

Stereocontrolled Total Synthesis of (−)‐Stemaphylline

Homologation of readily available α‐boryl pyrrolidines with metal carbenoids is especially challenging even when good leaving groups (Cl⁻) are employed. By performing a solvent switch from Et₂O to CHCl₃, efficient 1,2‐metalate rearrangement of the intermediate boronate occurs with both halide and ester leaving groups. The methodology was used in the total synthesis of the Stemona alkaloid (−)‐stemaphylline in just 11 steps (longest linear sequence), with high stereocontrol (>20:1 d.r.) and 11 % overall yield. The synthesis also features a late‐stage lithiation–borylation reaction with a tertiary amine containing carbenoid.     

Electrochemical preparation of some organotin compounds

Organotin dihalides R₂SnX₂ (X  Cl, Br, I) and their adducts with bidentate donor ligands have been prepared in high yield by the direct electrochemical reaction of metallic tin with alkyl or aryl halides in organic media at room temperature. Dimethyltin diiodide can be converted to tetramethyltin by reaction with methyl iodide at a cadmium anode. Electrochemical halide abstraction has been used to prepare R₆Sn₂ (R  Me, Ph) from the corresponding R₃Sn halide. The mechanism of these reactions is discussed.     

Chemo- and regioselective reductive opening of azetidinium ions

Enantiomerically pure azetidinium trifluoromethanesulfonates were opened by various hydride reagents. LiAlH₄ and NaBH₃CN reacted with a complete regioselectivity and the latter reagent also reacted in a chemoselective way, leaving unaffected an ester or a cyano moiety present in the substrate. This reaction provides 1,2-diamines, 1,2- and 1,4-amino alcohols or α-amino esters by combining proper choice of substrate and hydride reagent.     

Dihydrobenzoxazines and tetrahydroquinoxalines by a tandem reduction‐reductive amination reaction

A tandem reduction‐reductive amination reaction has been applied to the synthesis of 3,4‐dihydro‐2H‐1,4‐benzoxazines and 1‐acetyl‐1,2,3,4‐tetrahydroquinoxalines. The nitroketones required for the benzoxazine ring closures were prepared by (A) alkylation of the anion derived from 2‐nitrophenol with an allylic halide or (B) nucleophilic aromatic substitution of an allylic alkoxide on 2‐fluoro‐1‐nitrobenzene followed by ozonolysis. Precursors for the quinoxalines were prepared by alkylation of the anion of 2‐nitroacetanilide with an allylic halide followed by ozonolysis. Catalytic hydrogenation of the nitroketones using 5% palladium‐on‐carbon in methanol then gave the target heterocycles by a reduction‐reductive amination sequence. The N‐methyl derivatives for both ring systems were easily prepared by adding 5‐10 equivalents of aqueous formaldehyde prior to the reduction. The dihydrobenzoxazines were isolated in high yield following purification by chromatographic methods; tetrahydroquinoxalines were isolated in a similar manner and possessed differentiated functionality on the two nitrogens.     

Completely Amine-Free Open-Atmospheric Synthesis of High-Quality Cesium Lead Bromide (CsPbBr3) Perovskite Nanocrystals

Cesium lead halide perovskite nanocrystals (NCs) CsPbX₃ (X=Cl, Br, and I) have been prominent materials in the last few years due to their high photoluminescence quantum yield (PLQY) for light-emitting diodes and other significant applications in photovoltaics and optoelectronics. In colloidal CsPbX₃ synthesis, the most commonly used ligands are oleic acid and oleylamine. The latter plays an important role in surface passivation but may also be responsible for poor colloidal stability as a result of facile proton exchange leading to the formation of labile oleylammonium halide, which pulls halide ions out of the NC surface. Herein, a facile, efficient, completely amine-free synthesis of cesium lead bromide perovskite nanocrystals using hydrobromic acid as halide source and tri-n-octylphosphane as ligand under open-atmospheric conditions is demonstrated. Hydrobromic acid serves as labile source of bromide ion, and thus this three-precursor approach (separate precursors for Cs, Pb, Br) gives more control than a conventional single-source precursor for Pb and Br (PbBr₂). The use of HBr paved the way to eliminate oleylamine, and thus the formation of labile oleylammonium halide can be completely excluded. Various Cs:Pb:Br molar ratios were studied and optimum conditions for making very stable CsPbBr₃ NCs with high PLQY were found. These completely amine-free CsPbBr₃ perovskite NCs synthesized under bromine-rich conditions exhibit good stability and durability for more than three months in the form of colloidal solutions and films, respectively. Furthermore, stable tunable emission across a wide spectral range through anion exchange was demonstrated. More importantly, this work reports open-atmosphere-stable CsPbBr₃ NCs films exhibiting strong PL, which can be further used for optoelectronic device applications.     

Synthesis of heteropolynuclear Cu<Superscript>I</Superscript> and Pd<Superscript>II</Superscript> complexes with polymeric 2,2′-biquinoline-containing ligands and investigation of their catalytic activity in the Sonogashira couplings

A method for electrosynthesis of heteropolynuclear biquinoline-containing Cu^I and Pd^II complexes using sacrificial Cu and Pd anodes was developed. The sequence of anode dissolution (first Pd and then Cu) was important for the synthesis of the complex. The opposite sequence of dissolution resulted in oxidation of the initially formed Cu^I ions to Cu^II. The obtained Cu^I and Pd^II complexes with polymer ligands had high catalytic activity in the reaction of aryl halides with phenylacetylene giving rise to a C(sp²)-C(sp) bond. The yield of arylphenylacetylene in the presence of 0.1 mol.% of Pd catalyst in relation to the starting halide was 50–90% depending on the nature of the aryl halide.     

Regioselective Acylation of Cyclic α-Silylallyl Sulphide

Acylation of cyclic α-trimethylsilylallyl sulphide ( 3 ) by reaction with the acid halide catalyzed by aluminum chloride in CH₂Cl₃ at ?78°_C gave compound 4 in good yield with extremely high regio-selectivity.     

Magnesium Halide‐promoted Ring‐opening Reaction of Cyclic Ether in the Presence of Phosphine Halide

A new route to the direct preparation of H‐phosphinate esters has been explored. The ring‐opening reaction of cyclic ether (tetrahydrofuran or tetrahydropyrane) was carried out with magnesium halide in the presence of phosphine halide (PRCl₂ or PCl₃). The process is straightforward and all the reagents are relatively cheap and readily available. Magnesium halide‐mediated THF ring‐opening (S_N2@C) and the subsequent S_N2@P elementary reactions that giving rise to the intermediate of haloalkyl phosphinates have been discussed based on our experimental findings ( Path I : S_N2@C−+S_N2@P). Another possible route, the direct S_N2 between THF (nucleophile) and phosphine halide (electrophile) that followed by THF ring opening by halide dissociated from phosphine halide ( Path II: S_N2@P−+S_N2@C), was also proposed. However, path II is the least likely reaction path because neutral THF is not a good nucleophile. H‐phosphinate esters could be readily available in the subsequent hydrolysis process. Considering the ionic bond strength in magnesium halides and the nucleophilicity of halides dissociated from MgX₂ in protic solvents like water, MgBr₂ is recommended for ring‐opening reactions of cyclic ethers.     

Iron halide mediated atom transfer radical polymerization of methyl methacrylate with N‐alkyl‐2‐pyridylmethanimine as the ligand

The controlled atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) catalyzed by iron halide/N‐(n‐hexyl)‐2‐pyridylmethanimine (NHPMI) is described. The ethyl 2‐bromoisobutyrate (EBIB)‐initiated ATRP with [MMA]₀/[EBIB]₀/[iron halide]₀/[NHPMI]₀ = 150/1/1/2 was better controlled in 2‐butanone than in p‐xylene at 90 °C. Initially added iron(III) halide improved the controllability of the reactions in terms of molecular weight control. The p‐toluenesulfonyl chloride (TsC1)‐initiated ATRP were uncontrolled with [MMA]₀/[TsC1]₀/[iron halide]₀/[NHPMI]₀ = 150/1/1/2 in 2‐butanone at 90 °C. In contrast to the EBIB‐initiated system, the initially added iron(III) halide greatly decreased the controllability of the TsC1‐initiated ATRP. The ration of iron halide to NHPMI significantly influenced the controllability of both EBIB and TsC1‐initiated ATRP systems. The ATRP with [MMA]₀/[initiator]₀/[iron halide]₀/[NHPMI]₀ = 150/1//1/2 provided polymers with PDIs ≥ 1.57, whereas those with [iron halide]₀/[NHPMI]₀ = 1 resulted in polymers with PDIs as low as 1.35. Moreover, polymers with PDIs of approximately 1.25 were obtained after their precipitation from acidified methanol. The high functionality of the halide end group in the obtained polymer was confirmed by both ¹H NMR and a chain‐extenstion reaction. Cyclic voltammetry was utilized to explain the differing catalytic behaviors of the in situ‐formed complexes by iron halide and NHPMI with different molar ratios. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4882–4894, 2004     

Reduction of aromatic halides with sodium borohydride catalysed by titanium complexes. Unexpected role of air

Aromatic halide are reduced in high yield by reaction with NaBH₄ activated by a catalytic amount of Cp₂TiCl₂ or CpTiCl₃ in DMF in the presence of air; the reduction does not occur under a rigorously inert atmosphere.     

The coupling of organic groups by the electrochemical reduction of organic halides: Catalysis by 2,2′-bipyridinenickel complexes

The electrochemical reduction of a dilute solution of NiX₂bipy (bipy = 2,2′-bipyridine) in N-methylpyrrolidone gives the corresponding Ni⁰ complex, which undergoes oxidative addition with an excess of an organic halide RX to form RNiX. Decomposition of RNiX gives the dimer R₂ in good yield and nickel(II). The nickel(0) species is regenerated to give an electrocatalytic process. The possible mechanism of these reactions is discussed briefly.