Transformation of a hydroxyl into an acyl group on α-pyrone ring: a novel route to 3,4-diacylcoumarins

The transformation of a hydroxyl into an acyl group, a transformation which has been extensively investigated on the benzene nucleus of several substrates, is now applied successfully for the first time to a heterocyclic ring and specifically to the pyrone ring of coumarin to yield novel 3,4-diacylcoumarins in good yields. The reaction involves formation of a new C–C bond.     

Asymmetric Michael addition of malonates to enones catalyzed by a primary β-amino acid and its lithium salt

Highly enantioselective Michael addition of malonates to enones was achieved using a mixed catalyst consisting of a primary β-amino acid, O-TBDPS (S)-β-homoserine, and its lithium salt. Various cyclic and acyclic enones were converted into 1,5-ketoesters in high yields (up to 92%) with high enantioselectivity (up to 97% ee) under mild reaction conditions. Details of synthesis of the catalyst, optimization of the reaction conditions for the Michael addition reaction, and a plausible reaction mechanism are described.     

Highly regioselective control of 1,2-addition of organolithiums to α,β-unsaturated compounds promoted by lithium bromide in 2-methyltetrahydrofuran: a facile and eco-friendly access to allylic alcohols and amines

Very high regioselective 1,2-addition of organolithiums to α,β-unsaturated carbonyl-like compounds (ketones, aldehydes, and imines) in the presence of LiBr was achieved by carrying out reactions in the sustainable solvent 2-methyltetrahydrofuran. Excellent yields (in isolated product) of allylic alcohols and allylic amines were recovered under a simple experimental procedure at 0 °C.     

Reactivity of zirconocene and hafnocene dihydrides towards elemental selenium and sulfur. Strong evidence for insertion of a chalcogen unit into the metal—hydrogen bond

Dimeric metallocene dihydrides [(η⁵-t-BuC₅H₄)₂MH(μ-H)]₂ (1; M = Zr, Hf) react with elemental chalcogens to give the four-membered metallacycles [(η⁵-t-BuC₅H₄)₂M(μ-E)]₂ (2, E = Se; 3, E = S). In the case of sulfur, the reaction also gives (η⁵-t-BuC₅H₄)₂MS₅ (4). Both 3 and 4 are shown to come from subsequent reactions of the primary insertion product (η⁵-t-BuC₅H₄)₂M(SH)₂.     

Tandem β-fragmentation-intramolecular functionalization of alkoxyradicals. An approach to the synthesis of a and a'rings of limonin

A tandem β-fragmentation-intramolecular functionalization reaction is observed by photolysis of steroidal lactols in the presence of several oxidation agents under oxygen. An application of this reaction to the synthesis of A and A'rings of limonin (1) is described.     

Tandem chain extension–Mannich reaction: an approach to β-proline derivatives

A zinc carbenoid-initiated chain extension reaction provides access to an organometallic intermediate, which can be used to capture activated imines. Deprotection of the nitrogen and reduction provides access to racemic derivatives of β-proline. The relative stereochemistry of the β-proline can be controlled through use of different activating groups on the imine nitrogen.     

The migratory insertion of carbon monoxide and methyl isocyanide into zirconium–carbon and titanium–carbon bonds anchored to a calix[4]arene moiety: a dynamical density functional study

The energetics and reaction mechanism of the migratory insertion of carbon monoxide and methyl isocyanide into the zirconium–carbon and titanium–carbon bonds in [calix[4](OMe)₂(O)₂–M–Me₂], (M=Zr, Ti), have been investigated by combining static and dynamic density functional calculations. Two steps have been characterized: the coordination of the incoming nucleophilic moiety leading to relatively stable facial adducts; its subsequent insertion into the M–C bond, leading to ²-bound acyl or iminoacyl complexes, providing a rationale for the different behavior of CO and MeNC towards both insertion and deinsertion reactions. Our results indicate that the rate-determining step for the overall MeNC insertion into the M–C bond is its coordination to the electron-deficient metal center, with the titanium system featuring a higher energy barrier (12.7 versus 5.5 kcal mol^–1). Ab initio molecular dynamics simulations have been performed on the Zr system by means of the Car–Parrinello method, to study the hitherto inaccessible mechanistic features of the insertion reactions.Contribution to the Björn Roos Honorary Issue     

Synthesis of marine alkaloids leucettamines B and C by β-lactam ring rearrangement

A new method for the synthesis of marine alkaloids leucettamines B and C from Leucetta sp. sponges is described. The key step is the base-promoted rearrangement of β-lactam into imidazolone ring. Leucettamines B and C as well as their N-benzoyl derivatives were obtained in high yields. Single-crystal structures of both leucettamines B and C were determined by X-ray diffraction confirming Z-configuration of double bond at 4-position of imidazolone.     

A C-N insertion of β-lactam to benzyne: unusual formation of acridone

Intermolecular insertion of benzyne into the C-N bond of a β-lactam is described. This σ-insertion is followed by ring expansion that produces dihydroquinolinone, which rapidly reacts with an additional benzyne unit to afford an acridone through intramolecular C-C bond formation to the carbonyl group and rapid elimination of ethylene.     

Tandem Michael addition–Fries rearrangement of sorbylanilides: a convenient one pot synthesis of novel benzo[b]azocin-6-ones

The Letter pertains to an unprecedented tandem Michael addition–Fries rearrangement of sorbyl anilides resulting in a convenient one pot synthesis of novel benzo[b]azocin-6-ones. The reaction is thought to proceed via a δ-lactam intermediate, earlier considered un-reactive for Fries rearrangement. The proposed mechanism was further supported by examining the reactions of α,β-unsaturated anilides. Their inability to undergo any transformation under similar reaction conditions, especially the Fries–Michael rearrangement, indirectly validated the mechanism.     

Selective cconversion of pinane into β-pinene catalyzed by an iridium pentahydride complex

Pinane was catalytically converted into β-pinene with high selectivity by means of a soluble iridium pentahydride complex at 100°C in the presence of 3,3-dimethylbut-1-ene as hydrogen acceptor.     

Synthesis of novel and enantiomerically pure epoxypropylamine: a divergent route to the chiral β-adrenergic blocking agents

The chiral building block (S)-N-benzyl-N-isopropyl-2,3-epoxypropylamine is obtained by means of chlorohydroxylation of allylamine, followed by Jacobsen's hydrolytic kinetic resolution with water. A concise, divergent five-step synthesis of three β-adrenergic blocking agents in high enantiomeric excess using (S)-N-benzyl-N-isopropyl-2,3-epoxypropylamine as the key intermediate is described.     

Synthesis and characterization of a novel nanomagnetic phase-transfer catalyst and its application to regioselective synthesis of β-azido and β-nitro alcohols in water

Immobilization of polyethylene glycol-substituted 1-methylimidazolium bromide on the surface of magnetic Fe₃O₄ nanoparticles through hexane-1,6-diyldicarbamate linker afforded a powerful and reusable heterogeneous phase-transfer catalysis which was successfully used for regioselective ring opening of epoxides with azide and nitrite anions in aqueous medium. The new catalyst can readily be recovered by simple magnetic decantation and recycled several times without appreciable loss of catalytic activity.     

Modulation of animal and human hematopoiesis by β-glucans: a review

β-glucans are cell wall constituents of bacteria, yeast, fungi, and plants. They are not expressed in mammalian cells, but they are recognized by mammalian cells as pathogen-associated molecular patterns by pattern recognition receptors and thus act as biological response modifiers. This review summarizes data on the hematopoiesis-stimulating effects of β-glucans, as well as on their ability to enhance bone marrow recovery after an injury. β-glucans have been shown to support murine hematopoiesis suppressed by ionizing radiation or cytotoxic anti-cancer therapy. They also enhance stem cell homing and engraftment. Basically, two forms of β-glucan preparations have been investigated, namely particulate and soluble ones. β-glucans are generally well tolerated, the particulate forms showing a higher incidence of undesirable side effects. Taken together, the hematopoiesis-stimulating properties of β-glucans predetermine these biological response modifiers to ever increasing use in human medicinal practice.     

Conversion of Alcohols to Bromides by Trimethylsilane and lithium Bromide in Acetone

Conversion of alcohols to alkyl bromides is one of the most frequently used functional group transformation reactions. Phosphorus tribromide is one of the most popular classical reagents. Triphenylphosphine has been used in combination with bromine,carbon tetrabromide,N-halo imides and other bromide compounds as a mild reagents for the preparation of alkyl bromides. More reacently, halotrimethylsilanes were found to be useful for halogenation of alcohols. Geo- rge A.Olah successfully convert…     

Synthesis of novel β-aminocyclobutanecarboxylic acid derivatives by a solvent-free aza-Michael addition and subsequent ring closure

Novel β-aminocyclobutanecarboxylic acid derivatives were prepared via a sequential solvent-free aza-Michael addition of benzophenone imine across 3-halopropylidenemalonates and base-induced ring closure. These highly substituted cyclobutanedicarboxylic acid derivatives were subjected to a reactivity study which demonstrated the tendency of these donor-acceptor substituted four-membered rings to be converted into their corresponding ring-opened products.     

Synthesis and characterization of a novel amphiphilic copolymer containing β-cyclodextrin

In this article, maleic anhydride was used to attain the modified β-cyclodextrin (MAH-β-CD), and the MAH-β-CD was copolymerized with acrylamide (AM), acrylic acid (AA), and 2-acrylamido-2-methyl propane sulfonic acid (AMPS) via free radical copolymerization. The polymerization conditions were optimized through single-variable method. Subsequently, the copolymer structure was characterized through Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (¹HNMR) spectroscopy, and scanning electron microscopy (SEM). The three-dimensional network structure formed in aqueous solutions was observed via experimental results of SEM. Subsequently, several aspects of the properties of the copolymer, such as temperature tolerance, shear tolerance, salt resistance, and oil displacement ability, were investigated by comparing with hydrolyzed polyacrylamide (HPAM). Results indicate that the copolymer showed better performances than HPAM; thus, it could be concluded that the introduction of β-cyclodextrin in the polymer chain was helpful in enhancing the oil displacement efficiency in high-temperature and high-salinity oil field.     

Ring expansion reaction of α-sulfonyl cyclic ketones via insertion of arynes into C-C: a facile and mild access to medium- and large-sized benzannulated carbocycles

Insertion of arynes into C-C of α-sulfonyl ketones was investigated, which lead to the ring expansion reactions when α-sulfonyl cyclic ketones were used. By ring expansions and desulfonylations, medium- and large-sized benzannulated cyclic ketones were obtained in moderate yields.     

Gold catalysis: non-spirocyclic intermediates in the conversion of furanynes by the formal insertion of an alkyne into an aryl-alkyl cc single bond

It takes al-kynes: The formation of furyl-substituted heterocycles from furanynes with donor groups on the furan-alkyne tether and mechanistic control experiments indicate the involvement of open-chained carbenium ions in the overall insertion of an alkyne into a C?C bond, rather than the usual spirocyclic intermediates.     

Simultaneous Ring-Opened THF and insertion of diazoketone derived carbene into carbonyl O-H: Synthesis for β-keto enol ethers

A novel tandem synthesis of β-keto enol ethers was developed via the reaction of α-diazoketones, 1,3-diketones and THF catalyzed by cheap and available CuI under extremely simple conditions. During the course of the reaction, the ring-opened THF and diazocarbonyl derived carbene simultaneously inserted into O-H of 1,3-diketones.