One-pot synthesis of linear- and three-arm star-tetrablock quarterpolymers via sequential metal-free ring-opening polymerization using a “catalyst switch” strategy

A “catalyst switch” strategy has been used to sequentially polymerize four different heterocyclic monomers. In the first step, epoxides (1,2-butylene oxide and ethylene oxide) were successively polymerized from a monohydroxy or trihydroxy initiator in the presence of a strong phosphazene base promoter (t-BuP₄). Then, an excess of diphenyl phosphate (DPP) was introduced, followed by addition and polymerization of a cyclic carbonate (trimethylene carbonate) and a cyclic ester (δ-valerolactone or ε-caprolactone). DPP acted as both neutralizer of the phosphazenium alkoxide (polyether chain end) and activator of the cyclic carbonate/ester. Using this method, linear- and star-tetrablock quarterpolymers were prepared in one pot. This work is emphasizing the strength of the previously developed catalyst switch strategy for the facile metal-free synthesis of complex macromolecular architectures. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 304–312     

Optimization of Grignard ring-opening of α-brominated dioxolanes for the preparation of β-hydroxy-protected vinyl ethers by a three-step one-pot procedure

Aliphatic, cyclic, and aromatic benzoate-protected γ-hydroxy enol ethers were prepared from α-brominated dioxolanes by a three-step reaction procedure and a one-pot protocol involving Grignard reagent formation, ring-opening, and final benzoate protection. Additionally, tert-butyldiphenylsilyl, acetate, and 4,4′-dimethoxytrityl were also successfully used as alternative protecting groups.     

One-pot synthesis of 5-sulfonamidopyrazole from terminal alkynes, sulfonyl azides and hydrozones

5-Sulfonamidopyrazoles were efficiently synthesized from terminal alkynes, sulfonyl azides and hydrozones. The sequential reaction involves a copper-catalyzed three-component reaction, a Lewis acid-catalyzed electrocyclic reaction and a dehydrogenation.     

Rethinking Cysteine Protective Groups: S‐Alkylsulfonyl‐l‐Cysteines for Chemoselective Disulfide Formation

The ability to reversibly cross‐link proteins and peptides grants the amino acid cysteine its unique role in nature as well as in peptide chemistry. We report a novel class of S‐alkylsulfonyl‐l ‐cysteines and N‐carboxy anhydrides (NCA) thereof for peptide synthesis. The S‐alkylsulfonyl group is stable against amines and thus enables its use under Fmoc chemistry conditions and the controlled polymerization of the corresponding NCAs yielding well‐defined homo‐ as well as block co‐polymers. Yet, thiols react immediately with the S‐alkylsulfonyl group forming asymmetric disulfides. Therefore, we introduce the first reactive cysteine derivative for efficient and chemoselective disulfide formation in synthetic polypeptides, thus bypassing additional protective group cleavage steps.     

Ring-opening reactions of oxetanes: A review of methodology development and synthetic applications

Ring-opening reactions of oxetanes yield important functionalized products depending upon the nature of nucleophiles as well as substitution pattern on the oxetane ring. Ring opening of oxetanes can be carried out under a variety of reaction conditions. In this review article, an up-to-date overview of major synthetic methodologies involved in the ring opening of oxetanes as well as their synthetic applications has been presented.     

Ring opening metathesis polymerization of norbornene and tetracyclododecene with cyclooctene by using (arylimido)vanadium(V)–alkylidene catalyst

Ring opening metathesis polymerizations (ROMP) of norbornene (NBE), tetracyclododecene (TCD) in the presence of cis-cyclooctene (COE) using vanadium-alkylidene catalyst, V(CHSiMe₃)(N-2,6-Cl₂C₆H₃)(OC₆F₅)(PMe₃)₂ ( 1 ), were explored. The polymerizations with TCD afforded high-molecular-weight polymers (M_n = 19,500–47,400) with low PDI (M_w/M_n) values (1.18–1.38) which possess microstructure of repeated ring-opened TCD and certain methylene units by incorporation of ring-opened COE on the basis of microstructure analysis by NMR spectra and DSC thermograms; hydrogenated copolymer possessed melting temperature at 294 °C. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3067–3074     

Mutual Cooperation in the Formal Allyl Alcohol Nucleophilic Substitution and Hydration of Alkynes for the Construction of γ‐Substituted Ketones

Mutual cooperation in the formal allyl alcohol nucleophilic substitution reaction and hydration of an alkyne has been utilized in the presence of a gold catalyst to give a series of γ‐functionalized ketones with high to excellent yields. This reaction actually involved an intramolecular O?H insertion cyclization of an alkyne to form the dihydrofuran intermediate, which was followed by the nucleophilic addition ring‐opening of a dihydrofuran to give the target compound.     

Highly Efficient Aminolysis of Epoxides Catalyzed by Reusable Zirconyl Triflate,ZrO(OTf)2

Efficient ring opening of epoxides with aromatic amines catalyzed by ZrO(OTf)₂ is reported, and the corresponding β amino (beta-amino acid) alcohols were obtained in high yields in CH₃CN as solvent. The reactions were carried out at room temperature and in the presence of only 1.25 mol% of ZrO(OTf)₂. This catalyst can be reused several times without loss of its activity.     

Stimuli-responsive polypeptide materials prepared by ring-opening polymerization of α-amino acid N-carboxyanhydrides

Design and synthesis of biodegradable stimuli-responsive polypeptides are important areas considering their promising applications in biomedical fields. This article summarizes the most recent progresses in the development of stimuli-responsive polypeptide materials prepared via ring-opening polymerization of α-amino acid N-carboxyanhydrides. We discuss the design, synthesis and structure-property correlation of emerging materials including thermo-responsive, redox-responsive, photo-responsive and biomolecule responsive polypeptides. Considering the unique structural features of amino acids, we try to emphasize that the thermo-responsive properties not only depend on the amino acid structure but also rely on the secondary structures of polypeptides. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013