Palladium‐Catalyzed Two‐Component Domino Coupling Reaction of (Z)‐β‐Bromostyrenes with Norbornenes: Synthesis of 1,5‐Enynes

Polyfunctional molecules, 1,5‐enynes, have been achieved via a palladium(0)‐catalyzed domino coupling reaction of (Z)‐β‐bromostyrenes with norbornenes in the presence of cesium carbonate and N,N‐dimethylformamide. The process involves a double Heck‐type procedure, two‐fold C(sp²) H activation and formation of two carbon‐carbon bonds. There are possibilities of diversified transformation for the domino coupling of (Z)‐β‐bromostyrenes with norbornenes, the procedure is successfully driven to 1,5‐enynes via accurate adjustment of the reaction conditions.

     

Multi‐Enzymatic Synthesis of Optically Pure β‐Hydroxy α‐Amino Acids

A novel enzymatic production system of optically pure β‐hydroxy α‐amino acids was developed. Two enzymes were used for the system: an N‐succinyl L ‐amino acid β‐hydroxylase (SadA) belonging to the iron(II)/α‐ketoglutarate‐dependent dioxygenase superfamily and an N‐succinyl L ‐amino acid desuccinylase (LasA). The genes encoding the two enzymes are part of a gene set responsible for the biosynthesis of peptidyl compounds found in the Burkholderia ambifaria AMMD genome. SadA stereoselectively hydroxylated several N‐succinyl aliphatic L ‐amino acids and produced N‐succinyl β‐hydroxy L ‐amino acids, such as N‐succinyl‐L ‐β‐hydroxyvaline, N‐succinyl‐L ‐threonine, (2S,3R)‐N‐succinyl‐L ‐β‐hydroxyisoleucine, and N‐succinyl‐L ‐threo‐β‐hydroxyleucine. LasA catalyzed the desuccinylation of various N‐succinyl‐L ‐amino acids. Surprisingly, LasA is the first amide bond‐forming enzyme belonging to the amidohydrolase superfamily, and has succinylation activity towards the amino group of L ‐leucine. By combining SadA and LasA in a preparative scale production using N‐succinyl‐L ‐leucine as substrate, 2.3 mmol of L ‐threo‐β‐hydroxyleucine were successfully produced with 93% conversion and over 99% of diastereomeric excess. Consequently, the new production system described in this study has advantages in optical purity and reaction efficiency for application in the mass production of several β‐hydroxy α‐amino acids.

     

Palladium/Copper Bimetallic System‐Mediated Cross‐Coupling of Alkynes and Alkenes: Two Strategies to Suppress β‐H Elimination on Alkyl‐Palladium Center

This paper describes two efficient strategies to suppress β‐H elimination during the palladium/copper bimetallic system‐mediated cross‐coupling between alkynamides and alkenes. Remote donor groups with the terminal olefins, such as toluenesulfonamide, phosphate, sulfone, etc., cooperate with the amide of alkynamides and chelate the palladium active center, to promote C(sp³) O bond formation by suppressing the β‐H elimination. Another strategy uses the rigid structure of norbornene to make an intermediate without a syn‐β‐hydrogen to achieve reductive elimination of the C Cl bond.

     

Polyurethane foams with the contribution of products of hydroxyalkylation of N,N′‐bis(2‐hydroxyalkyl)oxamides with alkylene carbonates—obtaining and properties

In the reactions of N,N′‐bis(2‐hydroxyethyl)oxamide (BHEOD) with an excess of ethylene carbonate (EC) and N,N′‐bis(2‐hydroxypropyl)oxamide (BHPOD) with an excess of propylene carbonate (PC), the hydroxyethoxy and hydroxypropoxy derivatives of oxamide (OD) were obtained, respectively, distinguished by an increased thermal stability. First time, these derivatives were used as polyol components to obtain foamed polyurethane plastics with the contribution of 4,4′‐diisocyanate diphenylmethane (MDI). The rigid polyurethane foams of a slight water uptake, good stability of dimensions, enhanced thermal stability, and compression strength were obtained. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of α‐amino acid‐containing polyester: poly[(ε‐caprolactone)‐co‐(serine lactone)]

Novel polyesters, poly[(ε‐caprolactone)‐co‐(N‐trityl‐L ‐serine‐β‐lactone)]s, were prepared by copolymerizing ε‐caprolactone (CL) with N‐trityl‐L ‐serine‐β‐lactone (TSL) using ZnEt₂ as the catalyst. The number‐average molecular weights were determined which ranged from 2.7 × 10⁴ to 4.9 × 10⁴ Da with dispersity values ranging from 1.6 to 1.8. The structures of the copolymers were investigated by means of ¹H NMR, ¹³C NMR and infrared spectroscopies, thermogravimetric analysis and differential scanning calorimetry. The results indicated that CL and TSL monomer units were randomly distributed within the copolymer backbone structures and the ratios of TSL to CL in the copolymers were close to those in the feeds. After removal of the trityl group under mild condition, a new polyester with side amino groups provided by serine units was obtained. L929 cell culturing test indicated good biocompatibility of the polyester with or without protective groups. © 2012 Society of Chemical Industry     

Enantioselective Aza‐Morita–Baylis–Hillman Reaction Using Aliphatic α‐Amidosulfones as Imine Surrogates

The bifunctional catalyst 6′‐deoxy‐6′‐acylamino‐β‐isocupreidine ( 1 ) served both as a base to trigger the in situ generation of N‐sulfonylimine from readily available α‐amidosulfones and as a chiral nucleophile to initiate the enantioselective aza‐Morita–Baylis–Hillman (aza‐MBH) reaction. α‐Methylene‐β‐amino‐β‐alkyl carbonyl compounds, difficultly accessible previously, can now be synthesized in excellent yields and enantioselectivities.     

Efficiencies of various metallocene/reducing agent catalyst systems in the hydrogenation of polystyrene‐b‐polybutadiene‐b‐polystyrene block copolymers

Various metallocenes, including bis(η⁵‐cyclopentadienyl)cobalt, bis(η⁵‐cyclopentadienyl)nickel, and bis(η⁵‐cyclopentadienyl)titanium dichloride, combined with various reducing agents, including n‐butyllithium, phenyllithium, and triethylaluminum, have been evaluated for their catalytic efficiencies in the hydrogenation of polystyrene‐b‐polybutadiene‐b‐polystyrene (SBS) block copolymer. The efficiencies were determined by monitoring the extent of saturation of double bonds on the polybutadiene segment of the copolymer using FTIR and ¹H‐NMR spectroscopy. The cobaltocene/n‐butyllithium catalyst system was found the most active. The effects of H₂ pressure and the ratio of n‐butyllithium to cobaltocene ratio on the hydrogenation efficiency were also investigated. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1807–1815, 1999     

Access to Both Enantiomers of α‐Chloro‐β‐keto Esters with a Single Chiral Ligand: Highly Efficient Enantioselective Chlorination of Cyclic β‐Keto Esters Catalyzed by Chiral Copper(II) and Zinc(II) Complexes of a Spiro‐2,2′‐bischroman‐Based Bisoxazoline Ligand

The spiro‐2,2′‐bichroman‐based chiral bisoxazoline ligands (SPANbox) were found to be highly efficient in copper(II)‐ and zinc(II)‐catalyzed asymmetric chlorinations of cyclic β‐keto esters with N‐chlorosuccinimide (NCS) as the chlorination reagent, to give the corresponding α‐chloro‐β‐keto esters in excellent yields in 5–30 min with ee values up to 97%. The copper(II) triflate and zinc(II) triflate complexes of a single SPANbox ligand demonstrated complementary results to each other with respect to the enantioselection, affording both antipodes of the chlorinated product enantiomers with good to excellent optical purities.     

The preparation of α‐bis and α,ω‐tetrakis aromatic oxazolyl‐ and carboxyl‐functionalized polymers using 1,1‐bis[4‐(2‐(4,4‐dimethyl‐1,3‐oxazolyl))phenyl]ethylene in atom transfer radical polymerization reactions

The preparation of new compounds, 1,1‐bis[4‐(2‐(4,4‐dimethyl‐1,3‐oxazolyl))phenyl]ethanol and a new symmetrically disubstituted 1,1‐diphenylethylene derivative, 1,1‐bis[4‐(2‐(4,4‐dimethyl‐1,3‐oxazolyl))phenyl]ethylene, is described. 1,1‐Bis[4‐(2‐(4,4‐dimethyl‐1,3‐oxazolyl))phenyl]ethylene was utilized as a dioxazolyl initiator precursor for the polymerization of styrene by atom transfer radical polymerization (ATRP) methods to produce α‐bis(oxazolyl) polystyrene. The kinetic study of the polymerization process indicated that the free radical polymerization reaction for the preparation of α‐bis(oxazolyl) polystyrene follows first‐order rate kinetics with respect to monomer consumption. α,ω‐Tetrakis(oxazolyl) polystyrene was prepared by a new, in situ, controlled/living, post‐ATRP chain‐end‐functionalization reaction which involves the direct addition of 1,1‐bis[4‐(2‐(4,4‐dimethyl‐1,3‐oxazolyl))phenyl]ethylene to the ω‐terminus of the α‐bis(oxazolyl) polystyrene derivative, without the isolation and purification of the polymeric precursor. α‐Bis(carboxyl) and α,ω‐tetrakis(carboxyl) polystyrene derivatives were obtained by the quantitative chemical transformation of the oxazoline groups of the respective aromatic oxazolyl chain‐end‐functionalized polystyrene derivatives to the aromatic carboxyl groups. The organic precursor compounds, the dioxazolyl‐functionalized 1,1‐diphenylethylene derivative and the functionalized polymers were characterized using ¹H NMR and ¹³C NMR spectrometry and Fourier transform infrared spectroscopy, size‐exclusion and thin‐layer chromatography and non‐aqueous titration measurements. © 2014 Society of Chemical Industry     

Palladium‐Catalyzed Intramolecular Annulation of 3‐[2‐(2‐Iodobenzylamino)aryl]‐N‐arylpropiolamides: Synthesis of 3‐[5H‐Dibenzo[b,e]azepin‐11(6H)‐ylidene]indolin‐2‐ones

A novel palladium‐catalyzed intramolecular tandem annulation method is presented for the synthesis of 3‐[5H‐dibenzo[b,e]azepin‐11(6H)‐ylidene]indolin‐2‐ones. This method allows the conversion of various 3‐[2‐(2‐iodobenzylamino)aryl]‐N‐arylpropiolamides to the corresponding 3‐[5H‐dibenzo[b,e]azepin‐11(6H)‐ylidene]indolin‐2‐ones through the diarylation of an alkyne.     

Three‐Component Staudinger‐Type Stereoselective Synthesis of C‐Glycosyl‐β‐lactams and their Use as Precursors for C‐Glycosyl Isoserines and Dipeptides. A Polymer‐Assisted Solution‐Phase Approach

A collection of 4‐(C‐galactosyl)‐ and 4‐(C‐ribosyl)‐β‐lactams featuring different substituents at C‐3 and N‐1 was prepared by combining in a one‐pot procedure a formyl C‐glycoside, a primary amine, and a substituted acetyl chloride in the presence of base (Staudinger‐type reaction). Sulfonyl chloride and aminomethylated resins were used in sequence to remove excess of components and by‐products. Two pure C‐glycosyl‐β‐lactams were effectively transformed into C‐glycosyl‐N‐Boc‐β‐amino‐α‐hydroxy esters (C‐glycosyl isoserines) and a C‐ribosyl dipeptide via base‐promoted heterocycle ring opening by methanol and L ‐phenylalanine methyl ester, respectively.     

Highly Efficient Suzuki Coupling Reaction of α‐Chloroalkylidene‐β‐lactones and β‐Lactams with Organoboronic Acids

The activation of C Cl bond of (Z)‐α‐chloroalkylidene‐β‐lactones and (E)‐α‐chloroalkylidene‐β‐lactams via the Suzuki cross‐coupling reaction is reported in this paper. Alkyl, heteroaromatic, substituted phenyl‐ and alkenylboronic acids can be coupled with a wide variety of α‐chloroalkylidene‐β‐lactones and β‐lactams in excellent yields within a short period of time. The cross‐coupling reaction of optically active substrates leads to the optically active compounds without racemization of the corresponding chiral center.     

Highly (≥98%) Stereo‐ and Regioselective Trisubstituted Alkene Synthesis of Wide Applicability via 1‐Halo‐1‐alkyne Hydro‐ boration–Tandem Negishi–Suzuki Coupling or Organoborate Migratory Insertion

(Z)‐1‐Halo‐1‐alkenylboranes ( 7 ), preparable in 80–90% yields as ≥98% isomerically pure compounds via hydroboration of 1‐halo‐1‐alkynes, have been converted to a wide range of trisubstituted alkenes via three different routes in the tail‐to‐head ( T ‐to‐ H ) direction, i.e., (i) palladium‐catalyzed Negishi–Suzuki tandem alkenylation, (ii) treatment with organolithium or Grignard reagents to generate α‐bromo‐1‐alkenylboronate complexes that can undergo migratory insertion of a carbon group (R²) to form (E)‐alkenylboranes with inversion of alkene configuration (≥98% inversion), followed by fluoride‐promoted Suzuki alkenylation, and (iii) Negishi coupling to generate (Z)‐alkenylboranes in ≥98% retention of configuration, followed by treatment with organolithium or Grignard reagents to produce trisubstituted alkenes with reversed stereo configurations. The synthetic utility of the present methodology has been demonstrated in the highly selective synthesis of the side chain of scyphostatin in 28% yield over nine steps in the longest linear sequence from allyl alcohol. Thus, this new tandem protocol has been emerged as the most widely applicable and highly selective route to trisubstituted alkenes including those that are otherwise difficult to prepare.     

Palladium‐Catalyzed Efficient and One‐Pot Synthesis of Diarylacetylenes from the Reaction of Aryl Chlorides with 2‐Methyl‐3‐butyn‐2‐ol

An efficient and practical synthetic method has been developed for the preparation of symmetrical diarylacetylenes from the direct reaction of aryl chlorides with 2‐methyl‐3‐butyn‐2‐ol catalyzed by palladium(II) chloride‐bis(tricyclohexylphosphine) [PdCl₂(PCy₃)₂] under mild reaction conditions. Unsymmetrical diarylated acetylenes could be also obtained by using two different aryl chlorides simultaneously. The catalytic procedure includes a novel one‐pot palladium‐catalyzed, double Sonogashira coupling of inactivated aryl chlorides without use of copper(I) as co‐catalyst.     

Highly Enantioselective Phase‐Transfer Catalytic α‐Alkylation of α‐tert‐Butoxycarbonyllactams: Construction of β‐Quaternary Chiral Pyrrolidine and Piperidine Systems

A new enantioselective α‐alkylation of α‐tert‐butoxycarbonyllactams for the construction of β‐quaternary chiral pyrrolidine and piperidine core systems is reported. α‐Alkylations of N‐methyl‐α‐tert‐butoxycarbonylbutyrolactam and N‐diphenylmethyl‐α‐tert‐butoxycarbonylvalerolactam under phase‐transfer catalytic conditions (solid potassium hydroxide, toluene, −40 °C) in the presence of (S,S)‐3,4,5‐trifluorophenyl‐3,3′,5,5′‐tetrahydro‐2,6‐bis(3,4,5‐trifluorophenyl)‐4,4′‐spirobi[4H‐dinaphth[2,1‐c:1′,2′‐e]azepinium] bromide [(S,S)‐NAS Br] (5 mol%) afforded the corresponding α‐alkyl‐α‐tert‐butoxycarbonyllactams in very high chemical (up to 99%) and optical yields (up to 98% ee). Our new catalytic systems provide attractive synthetic methods for pyrrolidine‐ and piperidine‐based alkaloids and chiral intermediates with β‐quaternary carbon centers.     

Intramolecular Photochemical Cross‐Coupling Reactions of 3‐Acyl‐2‐haloindoles and 2‐Chloropyrrole‐3‐carbaldehydes with Substituted Benzenes

Highly efficient syntheses of indolo[2,1‐a]isoquinolines, indolo[2,1‐a][2]benzazepines, pyrrolo[2,1‐a]isoquinolines and pyrrolo[1,2‐a]benzazepines in excellent yields have been achieved by the intramolecular photochemical cross‐coupling reactions of 3‐acyl‐2‐halo‐N‐(ω‐arylalkyl)indoles and 2‐chloro‐N‐(ω‐arylalkyl)pyrrole‐3‐carbaldehydes in acetone. A new heterocyclic ring system – pyrrolo[1,2‐d][1,4]benzoxazepine – has also been constructed for the first time in this work by the photocyclization of 2‐chloro‐N‐(2‐phenoxyethyl)pyrrole‐3‐carbaldehyde.     

Synthesis of 3,4‐Disubstituted Quinolin‐2‐(1H)‐ones via Palladium‐Catalyzed Decarboxylative Arylation Reactions

The Pd‐catalyzed decarboxylative cross‐coupling reaction of 4‐substituted quinolin‐2(1H)‐one‐3‐carboxylic acids with (hetero)aryl halides is described. With palladium(II) bromide and triphenylarsine ligand as the catalyst system, a variety of 4‐substituted 3‐(hetero)aryl quinolin‐2(1 H)‐ones and related heterocycles, such as 4‐substituted 3‐arylcoumarins can be prepared in good to excellent yields.     

Pyrrole‐based narrow‐band‐gap copolymers for red light‐emitting diodes and bulk heterojunction photovoltaic cells

A series of narrow‐band‐gap conjugated copolymers (PFO‐DPT) derived from pyrrole, benzothiadiazole, and 9,9‐dioctylfluorene (DOF) is prepared by the palladium‐catalyzed Suzuki coupling reaction with the molar feed ratio of 4,7‐bis(N‐methylpyrrol‐2‐yl)‐2,1,3‐benzothiadiazole (DPT) around 1, 5, 15, 30, and 50%. The obtained polymers are readily soluble in common organic solvents. The solutions and the thin solid films of the copolymers absorb light from 300 nm to 600 nm with two absorbance peaks at around 380 nm and 505 nm. The PL emission consists mainly of DPT unit emission at around 624–686 nm depending on the DPT content in solid film. The EL emission peaks are red‐shifted from 630 nm for PFO‐DPT1 to 660 nm for PFO‐DPT50. Bulk heterojunction photovoltaic cells fabricated from composite films of copolymer and [6,6]‐phenyl C₆₁ butyric acid methyl ester (PCBM) as electron donor and electron acceptor, respectively, in device configuration: ITO/PEDOT : PSS/PFO‐DPT : PCBM/Ba/Al shows power conversion efficiencies 0.15% with open‐circuit voltage (V_oc) of 0.60 V and short‐circuit current density (J_sc) of 0.73 mA/cm² under AM1.5 solar simulator (100 mW/cm²). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Palladium Nanoparticles in Suzuki Cross‐Couplings: Tapping into the Potential of Tris‐Imidazolium Salts for Nanoparticle Stabilization

Inspired by the proclivity of various palladium sources to form nanoparticles in imidazolium‐based ionic liquids, we now report that tris‐imidazolium salts bearing hexadecyl chains and a bridging mesitylene moiety are potent stabilizers of palladium nanoparticles efficiently prepared via a Chaudret‐type hydrogenation of the bis(dibenzylideneacetone)palladium(0). The palladium nanoparticles have been isolated in pure form and characterized by ¹H nuclear magnetic resonance, transmission electron microscopy, electron diffraction and dynamic light scattering. The new materials proved effective in Suzuki cross‐coupling at a loading of 0.2% palladium. Thus, using a tris‐imidazolium iodide‐palladium material, a series of biaryl products has been prepared starting from aryl bromides and some activated chlorides. The possibility that this catalytic activity might be due to the formation of palladium N‐heterocyclic carbenes has been addressed through solid state ¹³C NMR and the synthesis of an imidazolium analogue in which the acidic 2‐H was replaced with a methyl group.     

Asymmetric Aza‐Morita–Baylis–Hillman‐Type Reactions: The Highly Enantioselective Reaction between Unmodified α,β‐ Unsaturated Aldehydes and N‐Acylimines by Organo‐co‐catalysis

The highly enantioselective organo‐co‐catalytic aza‐Morita–Baylis–Hillman (MBH)‐type reaction between N‐carbamate‐protected imines and α,β‐unsaturated aldehydes has been developed. The organic co‐catalytic system of proline and 1,4‐diazabicyclo[2.2.2]octane (DABCO) enables the asymmetric synthesis of the corresponding N‐Boc‐ and N‐Cbz‐protected β‐amino‐α‐alkylidene‐aldehydes in good to high yields and up to 99% ee. In the case of aza‐MBH‐type addition of enals to phenylprop‐2‐ene‐1‐imines, the co‐catalytic reaction exhibits excellent 1,2‐selectivity. The organo‐co‐catalytic aza‐MBH‐type reaction can also be performed by the direct highly enantioselective addition of α,β‐unsaturated aldehydes to bench‐stable N‐carbamate‐protected α‐amidosulfones to give the corresponding β‐amino‐α‐alkylidene‐aldehydes with up to 99% ee. The organo‐co‐catalytic aza‐MBH‐type reaction is also an expeditious entry to nearly enantiomerically pure β‐amino‐α‐alkylidene‐amino acids and β‐amino‐α‐alkylidene‐lactams (99% ee). The mechanism and stereochemistry of the chiral amine and DABCO co‐catalyzed aza‐MBH‐type reaction are also discussed.