Magnetic Nanoparticle‐Supported Morita–Baylis–Hillman Catalysts

A magnetic nanoparticle‐supported quinuclidine was prepared and evaluated as a recoverable Morita–Baylis–Hillman catalyst. The supported catalyst 2 demonstrated comparable activity with that of DABCO and could be simply recycled with the assistance of an external magnet. The thus recycled catalyst could be reused for 7 times without significant loss of activity.     

Tunable Bifunctional Phosphine–Squaramide Promoted Morita–Baylis–Hillman Reaction of N‐Alkyl Isatins with Acrylates

A series of highly tunable bifunctional phosphine‐squaramide H‐bond donor organocatalysts 6 has been synthesized from inexpensive and commercially available β‐amino alcohols in moderate yields. Catalyst 6 f can efficiently promote the asymmetric Morita–Baylis–Hillman (MBH) reaction of N‐alkyl isatins with acrylate esters providing the chiral 3‐substituted 3‐hydroxy‐2‐oxindoles in good yields and enantioselectivities (up to 93 % yield and 95 % ee), in which the challenging substrate tert‐butyl acrylate 9 d , provided the best ee value to date. Moreover, this methodology was applied successfully in the synthesis of chiral cyclic spiropyrrolizidineoxindole and γ‐butyrolactone derivatives without enantioselectivity deterioration. The possible mechanism of this MBH reaction was also investigated by ³¹P NMR, ESI‐MS and KIE studies. The KIE experiments show that the electrophilic addition of N‐methyl isatin to the complex of acrylate ester and phophine‐squaramide is the rate‐determing step of the asymmetric MBH reaction.

     

Chiral Thiourea‐Phosphine Organocatalysts in the Asymmetric Aza‐Morita–Baylis–Hillman Reaction

A new kind of bifunctional (thio)urea‐phosphine catalyst was synthesized and applied to the aza‐Morita–Baylis–Hillman reaction of N‐sulfonated imines with methyl vinyl ketone, phenyl vinyl ketone, ethyl vinyl ketone or acrolein. Moderate to excellent ee and yields of the products were obtained under mild reaction conditions.     

Chiral Phosphine‐Catalyzed Enantioselective [3+2] Annulation of Morita–Baylis–Hillman Carbonates with Cyclic 1‐Azadienes: Synthesis of Functionalized Cyclopentenes

With the use of a bifunctional chiral phosphine as the catalyst, the asymmetric [3+2] annulation of Morita–Baylis–Hillman carbonates with cyclic 1‐azadienes proceeded smoothly under mild conditions to give various enantiomerically enriched cyclopentene derivatives bearing three consecutive tertiary stereocenters and a sulfamate moiety in moderate to excellent yields with moderate to excellent enantioselectivities and excellent diastereoselectivities.

     

Rhodium‐Catalyzed [2+2+2] Cycloadditions of Diynes with Morita–Baylis–Hillman Adducts: A Stereoselective Entry to Densely Functionalized Cyclohexadiene Scaffolds

A rhodium‐catalyzed asymmetric synthesis of 5,5‐disubstituted cyclohexa‐1,3‐dienes has been achieved by [2+2+2] cycloaddition reactions between diynes and Morita–Baylis–Hillman (M‐B‐H) adducts as unsaturated substrates. Products containing two adjacent chiral centres (quaternary and tertiary, respectively) were obtained with complete diastereoselectivity and high enantioselectivity (84–97%) through a kinetic resolution of the M‐B‐H adduct. Furthermore, these highly substituted cyclohexadienes reacted with dienophiles to afford the corresponding Diels–Alder cycloadducts in good yields.

     

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.     

Palladium‐Catalyzed Domino Cyclization (5‐exo/3‐exo), Ring‐ Expansion by Palladium Rearrangement,and Aromatization: An Expedient Synthesis of 4‐Arylnicotinates from Morita–Baylis–Hillman Adducts

Various 4‐arylnicotinate derivatives were synthesized via a palladium‐catalyzed cascade reaction of N‐(2‐bromoallyl)‐N‐cinnamyltosylamides in a one‐pot procedure in good yields. The reaction involves a domino 5‐exo/3‐exo carbopalladation, ring‐expansion by palladium rearrangement, and an aromatization process.     

Dendritic Chiral Phosphine Lewis Bases‐Catalyzed Asymmetric Aza‐Morita–Baylis–Hillman Reaction of N‐Sulfonated Imines with Activated Olefins

A series of polyether dendritic chiral phosphine Lewis bases was synthesized, and successfully applied to the asymmetric aza‐Morita–Baylis–Hillman reaction of N‐sulfonated imines (N‐arylmethylidene‐4‐methylbenzenesulfonamides) with methyl vinyl ketone (MVK), ethyl vinyl ketone (EVK), and acrolein to give the adducts in good to excellent yields along with up to 97 % ee, which are more effective than our previously reported original chiral phosphine Lewis bases. In addition, the dendrimer‐supported chiral phosphine Lewis bases can be easily recovered and reused.     

Thermal Intramolecular [2+2] Cycloaddition: Synthesis of 3‐Azabicyclo[3.1.1]heptanes from Morita–Baylis–Hillman Adduct‐Derived 4,4‐Diaryl‐1,3‐dienes

Various 3‐azabicyclo[3.1.1]heptane derivatives were synthesized from Morita–Baylis–Hillman adduct‐derived 1,3‐dienes bearing a 4,4‐diaryl moiety through a thermal intramolecular [2+2] cycloaddition approach. By using the same approach, bicyclo[3.1.1]heptane, 3‐azabicyclo[3.2.0]heptane, and 3‐oxabicyclo[3.1.1]heptane derivatives could also be synthesized. A structurally similar dimethylallyl derivative underwent an intramolecular ene reaction to afford the pyrrolidine derivative.

     

Construction of Adjacent Quaternary and Tertiary Stereocenters via an Organocatalytic Allylic Alkylation of Morita–Baylis–Hillman Carbonates

Racemic Baylis–Hillman carbonates can be converted in densely functionalized products by reaction with cyano esters in the presence of a catalytic amount of a modified Cinchona alkaloid in high enantioselectivities and fair diastereoselectivities. A rational for the observed stereoselectivity is presented.     

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.     

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.     

Access to Stereodefined Trisubstituted Alkenes via Rhodium‐Catalyzed 1,4‐Addition of Potassium Trifluoro(organo)‐ borates to Baylis–Hillman Adducts

In the presence of a rhodium catalyst, unactivated Baylis–Hillman adducts reacted regioselectively with potassium trifluoro(organo)borates to afford stereodefined trisubstituted alkenes with good yields. This highly efficient reaction (aerobic conditions, low temperature, absence of added phosphane ligand) is believed to proceed via a 1,4‐addition/β‐hydroxy elimination mechanism.     

Polymer‐Supported Lewis Bases for the Baylis–Hillman Reaction

The use of polymer‐supported Lewis bases such as PEG₄₆₀₀‐(PPh₂)₂ and poly(DMAP) in the Baylis–Hillman reactions of N‐tosylimines (ArCHNTs) 1 or the corresponding arenecarbaldehydes with α,β‐unsaturated ketones has been investigated. The corresponding Baylis–Hillman adducts are obtained in good yields. The polymer‐supported Lewis bases can be easily recovered by filtration and the Lewis base PEG₄₆₀₀‐(PPh₂)₂ can be reproduced by reduction with LiAlH₄ and CeCl₃.     

First Copper‐Catalyzed Intramolecular Amidation in Substituted 4‐Iodopyrazoles Leading to the Synthesis of Pyrazolo[4,3‐b]‐ pyridin‐5‐ones

An unprecedented copper‐catalyzed intramolecular amidation of substituted 4‐iodopyrazoles generated either via Baylis–Hillman or Horner–Wadsworth–Emmons chemistry for the synthesis of pyrazolo[4,3‐b]pyridine‐5‐ones is described. In addition, the effect of the stereochemistry of the acrylamide on the cross‐coupling reaction has been investigated and it is demonstrated that only the Z‐isomer is favoured to undergo the intramolecular cyclization.     

Effect of hydrophobic monomer on the synthesis and swelling behaviour of a collagen‐graft‐poly[(acrylic acid)‐co‐(sodium acrylate)] hydrogel

BACKGROUND: Graft polymerization of vinylic monomers onto natural backbones is an efficient approach for the synthesis of natural‐based superabsorbents. The nature of the monomers will affect the swelling behaviour of the superabsorbents. Here, a novel superabsorbent was synthesized through grafting of acrylic acid onto collagen in the presence of hydrophobic styrene as co‐monomer. Subsequently, the effect of styrene on the swelling behaviour of the superabsorbent was studied. RESULTS: The highly swelling superabsorbent was prepared by introducing styrene into a collagen‐graft‐poly(acrylic acid) hydrogel. By inclusion of styrene monomer, the swelling capacity of the hydrogel was increased; this is discussed according to the network composition. The effect of swelling media (salt solutions and various pH values) was investigated. The results of absorbency under load showed that hydrogels containing phenyl groups exhibit better behaviour; however, by introducing styrene, the rate of water uptake and resistance to water holding under heating was reduced. Scanning electron micrographs of hydrogels revealed a decrease in porosity on using styrene. CONCLUSION: Inclusion of styrene monomer in the ionic superabsorbent caused high swelling capacity with better absorbency under load. This can be used to prepare highly swelling superabsorbents with good mechanical properties. The pH reversibility of the synthesized superabsorbent makes it a candidate for use in the controlled release of drugs and in agrochemicals. Copyright © 2008 Society of Chemical Industry     

Synthesis of pH‐ and temperature‐responsive chitosan‐graft‐poly[2‐(N,N‐dimethylamino) ethyl methacrylate] copolymer and gold nanoparticle stabilization by its micelles

Novel pH‐ and temperature‐responsive chitosan‐graft‐poly[2‐(N,N‐dimethylamino)ethyl methacrylate] (chitosan‐g‐PDMAEMA) copolymers were successfully synthesized by homogeneous atom transfer radical polymerization (ATRP) under mild conditions. Chitosan macroinitiator was prepared by phthaloylation of amino groups of chitosan and subsequent acylation of hydroxyl groups of chitosan with 2‐bromoisobutyryl bromide. The copolymers were obtained by ATRP of 2‐(N,N‐dimethylamino)ethyl methacrylate and they can self‐assemble into stable micelles in water. Hybrid micelles with a PDMAEMA corona incorporating gold nanoparticles (Au NPs) were prepared in situ via the reduction of HAuCl₄ with NaBH₄. The pH and temperature responses of the copolymer micelles and hybrid micelles were characterized using UV‐visible spectroscopy and dynamic laser light scattering. The morphology of the micelles was observed using transmission electron microscopy and atomic force microscopy. The PDMAEMA corona of the micelles acts as the ‘nanoreactor’ and the ‘anchor’ for the in situ formation and stabilization of Au NPs. Therefore, the spatial distribution of Au NPs within the micelles can be tuned by varying the temperature and pH value. Copyright © 2010 Society of Chemical Industry     

Synthesis and characterization of novel optically active poly(imide–urethane)s derived from N,N′‐(pyromellitoyl)‐bis‐(L‐leucine) diisocyanate and aromatic diols

N,N′‐(Pyromellitoyl)‐bis‐(L ‐leucine) diacid was reacted with ethyl chloroformate in the presence of triethylamine followed by reaction with activated sodium azide and gave N,N′‐(pyromellitoyl)‐bis‐(L ‐leucine) diacylazide in high yield. This diacylazide was heated in dry benzene and gave the unstable N,N′‐(pyromellitoyl)‐bis‐(L ‐leucine) diisocyanate ( 5 ) in quantitative yield. Thus, diisocyanate 5 was generated in situ and polycondensation reaction of this monomer with several aromatic diols, such as 4,4′‐dihydroxybiphenyl, 1,4‐hydroquinone, bisphenol A, phenolphthalein and 1,4‐dihydroxyanthraquinone, was performed in dry toluene under refluxing in the presence of 1,4‐diazabicyclo[2.2.2]octane (triethylenediamine) as a catalyst. The polymerization reactions proceeded within 48 h, producing a series of optically active poly(imide–urethane)s with good yield and moderate inherent viscosity in the range 0.18–0.28 dl g^?1. All of the above polymers were fully characterized by infrared spectra, elemental analyses and specific rotation. Some structural characterization and physical properties of these optically active poly(imide–urethane)s are reported Copyright © 2003 Society of Chemical Industry