A one-pot synthesis of constitutionally unsymmetrical rotaxanes using sequential Cu(I)-catalyzed azide-alkyne cycloadditions

A one-pot sequential Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) strategy is presented for the synthesis of constitutionally unsymmetrical cyclobis(paraquat-p-phenylene)-based rotaxanes in good yields from simple starting materials. The methodology consists of performing multiple CuAAC reactions to stopper a pseudorotaxane in a stepwise manner, the order of which is controlled through silyl-protection and Ag(I)-catalyzed deprotection of a terminal alkyne. The methodology is highlighted by the synthesis of an amphiphilic branched [4]rotaxane. The methodology increases the ability to access ever more complicated mechanically interlocked compounds to serve in devices as sophisticated and functional molecular machinery.     

Total synthesis of (+)-UCS1025A based on a sequential Michael-retro Michael strategy featuring one-pot six-step cascade reaction

The asymmetric total synthesis of UCS1025A is accomplished by establishing a novel and efficient method for the construction of a tricyclic pyrrolizidinone skeleton based on a sequential Michael-retro Michael strategy. The key step is a one-pot six-step cascade reaction including oxidation of a primary alcohol to the corresponding carboxylic acid, a retro thio-Michael reaction, and an intramolecular oxy-Michael reaction. This newly-developed synthetic strategy inspired by “masked” electrophilic character of tricyclic pyrrolizidinone is efficient and high-yielding compared to that developed in previously-reported total syntheses.     

A convenient one-pot synthesis of o-phenylene bis(diphenylphosphine)

The reaction between $\text{o}$-difluorobenzene and sodium diphenylphosphide in liquid ammonia provides a convenient synthesis of the title compound.     

Ligand effect in the synthesis of hyperbranched polymers via copper-catalyzed azide-alkyne cycloaddition polymerization (CuAACP)

Copper-catalyzed azide-alkyne cycloaddition polymerization (CuAACP) of AB₂ monomers demonstrated a chain-growth mechanism without any external ligand because of the complexation of in situ formed triazole groups with Cu catalysts. In this study, we explored the use of various ligands that affected the polymerization kinetics to tune the polymers’ molecular weights and the degree of branching (DB). Eight ligands were studied, including polyethylene glycol monomethyl ether (PEG₃₅₀, M_n = 350), tris(benzyltriazolylmethyl)amine (TBTA), 2,6-bis(1-undecyl-1H-benzo[d]imidazol-2-yl)pyridine (Py(DBim)₂), 2,2′-bipyridyl (bpy), 4,4′-di-n-nonyl-2,2′-bipyridine (dNbpy), N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA), N,N,N′,N″,N″-penta(n-butyl)diethylenetriamine (PBuDETA), and N,N,N′,N″,N″-pentabenzyldiethylenetriamine (PBnDETA). All ligands except PEG₃₅₀ exhibited stronger coordination with Cu(I) than the polytriazole polymer, which freed the Cu catalyst from polymers and resulted in dominant step-growth polymerization with simultaneous chain-growth feature. Meanwhile, the use of PEG₃₅₀ ligand retained the confined Cu in the polymer, demonstrating a chain-growth mechanism, but lower polymer molecular weights as compared with the no-external-ligand polymerization. Results indicated that aliphatic substituent groups on ligands had little effect on the molecular weights and DB of the polymers, but rigid aromatic substituent groups decreased both values. By varying the ligand species and amounts, hyperbranched polymers with DB value ranging from 0.53 ([TBTA]₀/[Cu]₀ = 5) to 0.98 ([PMDETA]₀/[Cu]₀ = 2) have been achieved. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2238–2244     

A novel one-pot three-component synthesis of 3-halofurans and sequential Suzuki coupling

A novel sequence of Sonogashira coupling and electrophilic addition to an ynone, with concomitant deprotection and cyclocondensation, opens a new one-pot synthesis of 3-halofurans; the method can be readily elaborated to a new sequential Sonogashira-addition-cyclocondensation-Suzuki reaction to furnish 2,3,5-trisubstituted furans in a one-pot fashion.     

A novel approach for the one-pot synthesis of linear and angular fused quinazolinones

A convenient and inexpensive one step methodology has been developed for the synthesis of linear and angular fused quinazolinones. The protocol, which uses amino heterocycles and o-bromo benzyl/naphthyl bromides as reactants, CuI as catalyst, Cs₂CO₃ as base, l-proline as ligand, and DMF as solvent, proceeds via nucleophilic aromatic substitution of the N-heteroaromatic cationic intermediate followed by in situ aerial oxidation at the benzylic position to the quinazolinone scaffold.     

Development of a one-pot sequential Sonogashira coupling for the synthesis of benzofurans

An efficient one-pot protocol was developed for the construction of the benzofuran system from aryl halides and protected iodophenols using carbinol-based acetylene sources. The sequence includes alternating palladium-catalyzed Sonogashira couplings and deprotection steps concluded by a ring closure. The developed one-pot procedure was compared with the stepwise approach and its efficiency was also demonstrated by the total synthesis of vignafuran, a benzofuran natural product.     

Formation of linear polymers in confined intranetwork space during synthesis of sequential semi-interpenetrating polymer networks

Sequential semi-interpenetrating polymer networks based on polyurethanes with different crosslink densities and linear polystyrene, poly(butyl methacrylate), and poly(methacrylic acid) have been studied. For the parent polyurethanes, the molecular mass of chain segments between crosslink junctions is estimated by the Flory-Rehner method. The kinetics of formation of linear polymers in semi-interpenetrating polymer networks is investigated as a function of the crosslink density of the polyurethane network. The molecular-mass distributions of linear polymers developed in semi-interpenetrating polymer networks are examined by size-exclusion chromatography. The relationship between the kinetics of formation of linear components under the conditions of confined space and their molecular mass is established.     

A five-component one-pot synthesis of phosphatidylinositol pentamannoside (PIM5)

A practical and efficient synthesis of phosphatidylinositol pentam annoside (PIM₅) was achieved based on a five-component one-pot sequential glycosylation protocol with exclusive regio- and stereo-selectivity.     

A novel strategy for the synthesis of 2-arylpyridines using one-pot 6π-azaelectrocyclization

A novel and useful method for the synthesis of 2-arylpyridines with a high efficiency and generality was achieved by utilizing the one-pot 6π-azaelectrocyclization followed by a base treatment. This is the first example of applying a sulfonamide to the azaelectrocyclization for efficient substituted pyridine synthesis.     

Dynamic ligand exchange of the lanthanide complex leading to structural and functional transformation: one-pot sequential catalytic asymmetric epoxidation-regioselective epoxide-opening process

The characteristic property of the lanthanide complex, which easily undergoes a dynamic ligand exchange and alters its structure and function in situ, is described. After the completion of the catalytic asymmetric epoxidation of various alpha,beta-unsaturated amides 2 in the presence of the Sm-(S)-BINOL-Ph3As=O (1:1:1) complex 1 (2-10 mol %), the addition of Me3SiN3 directly to the reaction mixture led to smooth epoxide-opening at room temperature, affording the corresponding anti-beta-azido-alpha-hydroxyamide 4 in excellent overall yield (up to 99%) with complete regioselectivity and excellent enantiomeric excess (up to >99%). The key to the success of the sequential process was the in situ generation of the highly reactive samarium azide complex through dynamic ligand exchange. In situ IR spectroscopy and other experiments provided strong evidence that the samarium azide complex was generated. In addition, the relatively high Lewis basicity of the amide moiety had a key role in the high reactivity of both the epoxidation and the epoxide-opening reactions. Examinations of other nucleophiles such as sulfur or carbon nucleophiles as well as transformations of epoxide-opened products are also described.     

One‐step synthesis of hyperbranched polyethylene macroinitiator and its block copolymers with methyl methacrylate or styrene via ATRP

Block copolymers of hyperbranched polyethylene (PE) and linear polystyrene (PS) or poly(methyl methacrylate) (PMMA) were synthesized via atom transfer radical polymerization (ATRP) with hyperbranched PE macroinitiators. The PE macroinitiators were synthesized through a “living” polymerization of ethylene catalyzed with a Pd‐diimine catalyst and end‐capped with 4‐chloromethyl styrene as a chain quenching agent in one step. The macroinitiator and block copolymer samples were characterized by gel permeation chromatography, ¹H and ¹³C NMR, and differential scanning calorimetry. The hyperbranched PE chains had narrow molecular weight distribution and contained a single terminal benzyl chloride per chain. Both hyperbranched PE and linear PS or PMMA blocks had well‐controlled molecular weights. Slow initiation was observed in ATRP because of steric effect of hyperbranched structures, resulting in slightly broad polydispersity index in the block copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3024–3032, 2010     

A method for determining the molecular weight of hyperbranched polymers

A method for determining the molecular weight of hyperbranched polymers is developed, based on the measurement of the area of the monolayer at the water/air interface.     

Crazing of polymers in the presence of hyperbranched poly(ethoxysiloxane)

The crazing of various polymers (PET, isotactic PP, and HDPE) in the presence of branched poly(ethoxysiloxane) and its low-molecular-mass analog—tetraethoxysilane—has been studied. The hyperbranched poly(ethoxysiloxane) is shown to be an effective adsorptionally active medium for crazing of various solid polymers and development of nanoporous structures with a volume porosity of up to 60%. Depending on the nature of polymers, two mechanisms of crazing (either classical or delocalized crazing) can take place. The reactions of hydrolysis (basic and acidic) within the pores leading to formation of solid silica have been performed. Electron microscopic observations provide evidence that the transformation of a viscous adsorptionally active liquid into a solid compound directly within the volume of a polymer matrix leads to the stabilization of a highly dispersed polymer structure that arises in the course of crazing.     

Functionalized hyperbranched grafts on polyethylene powder for support of Pd(0)-phosphine catalyst

Hyperbranched grafts of poly(acrylic acid) have been modified with phosphine ligands for support of Pd(0) for use in allylic substitution chemistry.