Copper-catalyzed coupling reactions of alkenyl halides with alkynes in the absence of palladium and ligand

We report herein copper(I)-catalyzed cross-coupling reactions of alkenyl halides with alkynes for the synthesis of 2-alkynyl-buta-1,3-dienes in good to excellent yields. This procedure is the first example for the synthesis of enynes catalyzed by catalytic amount of copper(I) alone in the absence of palladium and any ligand at relatively lower temperature.     

Ruthenium-catalyzed reaction of alkenyl triflates with zinc thiolates

A ruthenium complex coordinated with 3,4,7,8-tetramethyl-1,10-phenanthroline catalyzed the reaction of alkenyl triflates with zinc dithiolates to give alkenyl sulfides.     

Suzuki-Miyaura cross-coupling of alkenyl tosylates with alkenyl MIDA boronates

A practical procedure for the palladium-catalysed Suzuki-Miyaura coupling of various alkenyl tosylates with alkenyl MIDA boronates has been developed. Commercially available trans-bromo[N-succinimidyl-bis(triphenylphosphine)]palladium(II) [Pd(PPh₃)₂NBS] is an effective catalyst under the slow release conditions of MIDA boronates; with less activated alkenyl tosylates addition of the cheap, air-stable tricyclohexylphosphine tetrafluoroborate enhances reactivity.     

Copper-catalyzed radical oxytrifluoromethylation of alkenyl oximes at ambient temperature

A mild and efficient copper-catalyzed radical oxytrifluoromethylation reaction of alkenyl oximes was successfully developed. The method provides a straightforward access to a wide range of CF₃-containing isoxazolines in good to excellent yields.     

Ring-rearrangement metathesis of substituted dihydropyrans and dihydrofurans

The rearrangement of dihydropyrans and dihydrofurans featuring appending olefins has been studied. The rearranged products bear resemblance with polyunsaturated di- and trisaccharides. Examples of functionalization prior to, or following, rearrangement are provided suggesting that the method should be useful for the synthesis of nonclassical saccharides. This work also illustrates the power of cascade methatetic processes for increasing molecular complexity starting from relatively simple heterocycles.     

Ring-rearrangement metathesis of bicyclic amino acid derivatives

In this letter, we describe the ring-rearrangement metathesis (RRM) of bicyclic amino acid derivatives. The procedure is of use for the synthesis of constrained amino acid and peptide derivatives with potential as reverse-turn inducers.     

Ring-closing olefin metathesis reactions; synthesis of iso-β-bisabolol

A ring-closing olefin metathesis is the key step in a synthesis of the rare iso-β-bisabolol found in sandalwood oils.     

Ene-yne metathesis of polyunsaturated norbornene derivatives

Norbornene derivatives bearing endo-substituents in the 5- and 6-positions were studied as substrates for ene-yne metathesis cascades. Substrates which contained an internal alkyne and a terminal alkene or alkyne in each sidechain were found to undergo a metathesis cascade leading to pentacyclic bis-dienes and bis-trienes. Attempts to extend the chemistry further to sidechains containing two internal alkynes or two internal alkynes and a terminal alkene were not successful with the first generation Grubbs' catalyst. However, the substrate containing two internal alkynes did react with the second generation Grubbs' catalyst to give a tetra-diene containing product.     

Understanding the effect of allylic methyls in olefin cross-metathesis

A series of NMR spectroscopy experiments have been conducted with both the model compound, 3-methyl-1-pentene and the corresponding ADMET monomer 3,6,9-trimethylundeca-1,10-diene (11) to better understand the effect of allylic methyls during olefin metathesis chemistry. Traditional ADMET catalysts such as Schrock’s molybdenum (1), and Grubbs’ ruthenium 1st and 2nd generation (2 and 3) were examined under cross-metathesis and ADMET conditions. Regardless of catalyst selection, 50% or less metathesis conversion was observed for all reactions, especially in the case of the more sterically encumbered diene. With Schrock’s molybdenum catalyst 1, the reaction leads to an accumulation of the non-productive metallacyclobutane, trapping the catalyst in an inactive form. With Grubbs’ ruthenium catalysts 2 and 3, the substrate coordinates to the metal center primarily to yield non-productive metathesis, which results in a build-up of the methylidene complex leading to catalyst decomposition. These results are directly correlated to the orientation of the substrate’s bulk during the metallacyclobutane formation, the alkyl branch being adjacent to the metal center in the case of the molybdenum catalyst 1, and opposite to it in the case of ruthenium catalyst 2 and 3.     

Synthesis of C-C bonded dimeric steroids by olefin metathesis

Five new C-C bonded steroidal homodimers derived from deoxycholic acid, pregnenolone, and progesterone were synthesized by an olefin metathesis reaction assisted by microwave heating. Microwave improved the yield and accelerated the reaction allowing the use of less catalyst with good results (2.5 mol %). Due to the bulky nature of the steroidal skeleton the more favorable E-dimers were formed as the sole or major products depending on the linker length.     

Synthesis and Enzymatic Degradation of Nylon 66 Copolymers with Poly(Ethyleneglycol)s

Abstract

Nylon 66 (N66) copolymers were prepared by melt polycondensation of adipic acid and hexamethylenediamine with 5–80 mol% poly(ethylene glycol) (PEG), where the molecular weight (MW) of PEG was 200–1000. The reduced specific viscosity of the copolymers was increased by the copolymerization. The crystallinity and melting temperature (T _m) of N66 components decreased with increasing PEG content, but T _m depression of copolymers at the same mole content decreased with increasing MW of PEG, suggesting that the copolymer structures are not of the random type but of the block type at the higher MW of PEG. The water absorption increased with increasing PEG content, and its increase was much higher at the higher MW of PEG. The enzymatic degradation was estimated by the weight loss of copolymer films in the buffer solution with and without a lipase at 37°C. The weight loss was enhanced appreciably by the presence of a lipase, and increased abruptly at higher PEG content, which was correlated to water absorption and the concentration of ester linkages. The enzymatic degradation of these N66 copolymers was much higher than that of previously reported PET copolymers with PEG. The abrupt increase of weight loss by alkali hydrolysis was fairly comparable to that of water absorption.     

Acyclic diene metathesis polymerization of tailor-made monomers towards sequence-regulated vinyl copolymers

 Acyclic diene metathesis polymerization (ADMET) enables convenient transfer of sequential information of the designed monomers to the corresponding sequence-regulated copolymers. In this study, two structurally symmetric monomers, M1 and M2, were synthesized via atom transfer radical addition (ATRA) of diethyl meso-2,5-dibromohexanedioate with 1,5-hexadiene and 1,7-octadiene, respectively. Thus, sequenced segment of VB-EA-EA-VB (VB and EA represent vinyl bromide and ethyl acrylate, respectively) was incorporated into the ADMET diene monomers. ADMET polymerization of these two monomers with Grubbs first generation catalyst (Grubbs-I) was performed in CH₂Cl₂ at 40℃ for 5 days under nitrogen purge. Effects of catalyst amount, monomer concentration and methanol precipitation on the M_p and PDI of polymers were investigated by GPC, and the structures of the formed polymers were characterized by NMR. Our results indicate that using 3.0 mol% of Grubbs-I to monomer can afford polymers with high M_p. Moreover, selective precipitation in methanol enables complete removal of low molecular weight components from the crude products. Meanwhile, M2 exhibits higher ADMET polymerization reactivity than M1 due to its capability of suppressing negative neighboring group effect.     

Preparation of starch and laponite co-stabilized alkenyl succinic anhydride emulsions for paper sizing

Stable alkenyl succinic anhydride (ASA) emulsions with approximately 25% of ASA were prepared by using native maize starch and laponite particles as stabilizers. The morphology, sizing performance, and storage stability of the as-prepared ASA emulsions were evaluated. It was surprisingly found that the introduction of laponite particles could significantly improve the emulsion stability, reduce the emulsion droplet size, and enhance the sizing performance, while the occurrence of native maize starch depresses the deterioration of the ASA emulsion in sizing performance with increasing emulsion storage time.     

Comparison of alkenyl succinic anhydride emulsions stabilized by laponite modified with ethylamine,diethylamine and triethylamine

The modifications of laponite particles with three short amines, that is, ethylamine, diethylamine and triethylamine, were compared and the amine-modified laponites were used to stabilize alkenyl succinic anhydride emulsions. The results show that the emulsion stability can be improved while the emulsion droplet size can be reduced by using the amines to modify laponite particles. Among the three amines, the diethylamine exerts the largest while the triethylamine exerts the smallest effects on the zeta potential of laponite, the turbidity of laponite aqueous dispersion and the emulsion stability and morphology. The emulsion with the smallest droplet size shows the highest sizing performance.     

Synthesis of dienynes from alkenes and diynes using ruthenium-mediated ring-closing metathesis

This communication describes a novel ruthenium-mediated transformation, which converts molecules containing alkenes and conjugated diynes such as 1-allyl-2-{[6-(2-allylphenoxy)-2,4-hexadiynyl]oxy}benzene into dienynes such as 3-[2-(2,5-dihydro-1-benzoxepin-3-yl)-1-methylene-2-propenyl]-2,5-dihydro-1-benzoxepine instead of the expected product 3-[2-(2,5-dihydro-1-benzoxepin-3-yl)ethynyl]-2,5-dihydro-1-benzoxepine.     

Synthesis of spirocyclic butenolides by ring closing metathesis

Spirocyclic butenolides were efficiently prepared by a ring closing metathesis strategy.     

The first total synthesis of sequosempervirin A through an orthoester Claisen rearrangement—ring closing metathesis sequence

The first total synthesis of sequosempervirin A, a norlignan with a unique spirocyclic structure has been accomplished using an orthoester Claisen rearrangement—ring closing metathesis sequence.     

Use of the olefin metathesis reaction for highly efficient β-cyclodextrin modification

A series of novel primary face mono-substituted β-cyclodextrin derivatives have been synthesised using the olefin metathesis reaction. Mono-6-allylamino-6-deoxy-β-cyclodextrin easily synthesised by nucleophilic substitution of mono-6-tosyl-β-cyclodextrin is the key synthon in the preparation of cyclodextrin derivatives mono-functionalised at the primary face by alkyl, aryl or perfluoroalkyl groups using Grubbs catalyst. In the cases of vinylbenzene and 1H,1H,2H-perfluoro-1-octene, the metathesis reactions yield with 95% stereoselectivity of the E-isomer.     

Applications of metathesis in heterogeneous catalysis and separation sciences

During the last 15 years, the area of well-defined metathesis initiator systems was characterized by almost dramatic improvements in terms of initiator activity, stability, and selectivity. In due consequence, control over polymer properties increased and metathesis-based polymerization techniques (in particular ring-opening metathesis polymerization, ROMP) have been adapted for materials science purposes. Quite recently, metathesis-based supports have entered the fields of heterogeneous catalysis as well as separation and life sciences. In this review, both the synthesis and properties of metathesis-based well-defined catalytic supports and separations systems shall be summarized. Special consideration will be given to the particular structural features that have been made possible using ROMP.     

Annulated butanolides by ring closing metathesis of diallyltetronic acid derivatives

3,3-Diallyldihydrofuran-2,4-diones 5 with two identical allyl residues were obtained by Tsuji-Trost-type Pd-catalysed allylation of either 4-O-allyltetronates or 3-allyltetronic acids. Allylation of sodium 3-allyltetronate with a second allyl acetate gave mixed derivatives 5 as did the Claisen rearrangement of 4-O-allyl 3-allyltetronates 6 under microwave conditions. Compounds 5 and 6 were converted to butanolides with 3,3-spirocyclopentenyl or 3,4-cycloalkanyl annulation by ring closing metathesis with Grubbs catalysts.