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1. Effects of temperature on chaotropic anion-induced shape transitions of star molecular bottlebrushes with heterografted poly(ethylene oxide) and poly( N , N -dialkylaminoethyl methacrylate) side chains in acidic water

   https://doi.org/10.1039/D1SM00728A  

   Lewoczko, Evan M. ; Kelly, Michael T. ; Kent, Ethan W. ; Zhao, Bin ( July 2021 , Soft Matter)

   null (Ed.)

   This article reports a study of the effects of temperature on chaotropic anion (CA)-induced star-globule shape transitions in acidic water of three-arm star bottlebrushes composed of heterografted poly(ethylene oxide) (PEO) and either poly(2-( N , N -dimethylamino)ethyl methacrylate) (PDMAEMA) or poly(2-( N , N -diethylamino)ethyl methacrylate) (PDEAEMA) (the brushes denoted as SMB-11 and -22, respectively). The brush polymers were synthesized by grafting alkyne-end-functionalized PEO and PDMAEMA or PDEAEMA onto an azide-bearing three-arm star backbone polymer using the copper( i )-catalyzed alkyne-azide cycloaddition reaction. Six anions were studied for their effects on the conformations of SMB-11 and -22 in acidic water: super CAs [Fe(CN) 6 ] 3− and [Fe(CN)6] 4− , moderate CAs PF 6 − and ClO 4 − , weak CA I − , and for comparison, kosmotropic anion SO 4 2− . At 25 °C, the addition of super and moderate CAs induced shape transitions of SMB-11 and -22 in pH 4.50 water from a starlike to a collapsed globular state stabilized by PEO side chains, which was driven by the ion pairing of protonated tertiary amine groups with CAs and the chaotropic effect. The shape changes occurred at much lower salt concentrations for super CAs than moderate CAs. Upon heating from near room temperature to 70 °C, the super CA-collapsed brushes remained in the globular state, whereas the moderate CA-collapsed brushes underwent reversible globule-to-star shape transitions. The transition temperature increased with increasing salt concentration and was found to be higher for SMB-22 at the same salt concentration, presumably caused by the chaotropic effect. In contrast, I − and SO 4 2− had small effects on the conformations of SMB-11 and -22 at 25 °C in the studied salt concentration range, and only small and gradual size variations were observed upon heating to 70 °C. The results reported here may have potential uses in the design of stimuli-responsive systems for substance encapsulation and release. 

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2. Alkynyl Prins and Alkynyl Aza-Prins Annulations: Scope and Synthetic Applications

   https://doi.org/10.1055/s-0039-1690869  

   Abdul-Rashed, Shukree ; Holt, Connor ; Frontier, Alison J. ( July 2020 , Synthesis)

   This review focuses on alkynyl Prins and alkynyl aza-Prins cyclization­ processes, which involve intramolecular coupling of an alkyne with either an oxocarbenium or iminium electrophile. The oxocarbenium or iminium species can be generated through condensation- or elimination-type processes, to achieve an overall bimolecular annulation that enables the synthesis of both oxygen- and nitrogen-containing­ saturated heterocycles with different ring sizes and substitution patterns. Also discussed are cascade processes in which alkynyl Prins heterocyclic adducts react to trigger subsequent pericyclic reactions, including [4+2] cycloadditions and Nazarov electrocyclizations, to rapidly construct complex small molecules. Finally, examples of the use of alkynyl Prins and alkynyl aza-Prins reactions in the synthesis of natural products are described. The review covers the literature through the end of 2019. 1 Introduction 1.1 Alkyne-Carbonyl Coupling Pathways 1.2 Coupling/Cyclization Cascades Using the Alkynyl Prins Reaction 2 Alkynyl Prins Annulation (Oxocarbenium Electrophiles) 2.1 Early Work 2.2 Halide as Terminal Nucleophile 2.3 Oxygen as Terminal Nucleophile 2.4 Arene as Terminal Nucleophile (Intermolecular) 2.5 Arene Terminal Nucleophile (Intramolecular) 2.6 Cyclizations Terminated by Elimination 3 Synthetic Utility of Alkynyl Prins Annulation 3.1 Alkynyl Prins-Mediated Synthesis of Dienes for a [4+2] Cyclo­- addition­-Oxidation Sequence 3.2 Alkynyl Prins Cyclization Adducts as Nazarov Cyclization Precursors 3.3 Alkynyl Prins Cyclization in Natural Product Synthesis 4 Alkynyl Aza-Prins Annulation 4.1 Iminium Electrophiles 4.2 Activated Iminium Electrophiles 5 Alkynyl Aza-Prins Cyclizations in Natural Product Synthesis 6 Summary and Outlook 

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3. Azide‐Terminated RAFT Polymers for Biological Applications

   https://doi.org/10.1002/cpch.85  

   Jiang, Ziwen ; He, Huan ; Liu, Hongxu ; Thayumanavan, S. ( November 2020 , Current Protocols in Chemical Biology)

   Reversible addition‐fragmentation chain‐transfer (RAFT) polymerization is a commonly used polymerization methodology to generate synthetic polymers. The products of RAFT polymerization, i.e., RAFT polymers, have been widely employed in several biologically relevant areas, including drug delivery, biomedical imaging, and tissue engineering. In this article, we summarize a synthetic methodology to display an azide group at the chain end of a RAFT polymer, thus presenting a reactive site on the polymer terminus. This platform enables a click reaction between azide‐terminated polymers and alkyne‐containing molecules, providing a broadly applicable scaffold for chemical and bioconjugation reactions on RAFT polymers. We also highlight applications of these azide‐terminated RAFT polymers in fluorophore labeling and for promoting organelle targeting capability. © 2020 Wiley Periodicals LLC.

   Basic Protocol 1: Synthesis of the azide derivatives of chain transfer agent and radical initiator

   Basic Protocol 2: Installation of an azide group on the α‐end of RAFT polymers

   Alternate Protocol: Installation of an azide group on the ω‐end of RAFT polymers

   Basic Protocol 3: Click reaction between azide‐terminated RAFT polymers and alkyne derivatives

    

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4. Regioselective Formation of Substituted Indoles: Formal Synthesis of Lysergic Acid

   https://doi.org/10.1002/chem.202004107  

   Points, III, Gary L. ; Stout, Kenneth T. ; Beaudry, Christopher M. ( November 2020 , Chemistry – A European Journal)

   A Diels–Alder reaction‐based strategy for the synthesis of indoles and related heterocycles is reported. An intramolecular cycloaddition of alkyne‐tethered 3‐aminopyrones gives 4‐substituted indolines in good yield and with complete regioselectivity. Additional substitution is readily tolerated in the transformation, allowing synthesis of complex and non‐canonical substitution patterns. Oxidative conditions give the corresponding indoles. The strategy also allows the synthesis of carbazoles. The method was showcased in a formal synthesis of lysergic acid.

    

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5. Arenophile-Mediated Photochemical Dearomatization of Nonactivated Arenes

   https://doi.org/10.2533/chimia.2020.577  

   Okumura, Mikiko ; Sarlah, David ( August 2020 , CHIMIA International Journal for Chemistry)

   null (Ed.)

   Aromatic compounds are one of the most abundant classes of organic molecules and find utility as precursors for alicyclic hydrocarbon building blocks. While many established dearomatization reactions are exceptionally powerful, dearomatization with concurrent introduction of functionality, i.e. dearomative functionalization, is still a largely underdeveloped field. This review aims to provide an overview of our recent efforts and progress in the development of dearomative functionalization of simple and nonactivated arenes using arenophile-arene cycloaddition platform. These cycloadducts, formed via a visible-light-mediated [4+2]-photocycloaddition, can be elaborated in situ through olefin chemistry or transition-metal-catalyzed ring-opening with carbon-, nitrogen-, and oxygen-based nucleophiles, providing access to diverse structures with functional and stereochemical complexity. Moreover, the dearomatized products are amenable to further elaborations, which effectively install other functionalities onto the resulting alicyclic carbocycles. The utility of the arenophile-mediated dearomatization methods are also highlighted by the facile syntheses of natural products and bioactive compounds through novel disconnections. 

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