Betaine–N-Heterocyclic Carbene Interconversions of Quinazolin-4-One Imidazolium Mesomeric Betaines. Sulfur, Selenium, and Borane Adduct Formation

Reaction of N-alkylated imidazoles with 2-chloro-4-quinazolinone gave mesomeric betaines, 2-(1-alkyl-1H-imidazolium-3-yl)quinazolin-4-olates, for which three tautomeric forms of N-heterocyclic carbenes (NHCs) can be formulated, in addition to an anionic NHC after deprotonation. The NHC tautomers were trapped with sulfur, selenium, triethylborane, and triphenylborane as thiones, selenones and borane adducts, respectively. We obtained two isomers of the cyclic borane adducts, diazaboroloquinazolinones with [1,5-a] and [5,1-b]-type fusion between the quinazolinone and the diazaborole rings. They correspond to two different NHC tautomers and to the anionic NHC derived thereof. The third NHC tautomer was trapped as a non-cyclic adduct with tris(pentafluorophenyl)borane by coordination to the quinazoline oxygen atom. 2D 1H-15N HMBC experiments of 15N-labeled quinazolinone fragments, quantitative measurements of long-range 1H-15N coupling constants (JHN), and five X-ray single crystal analyses have been carried out for the structure elucidations and to gain insight into the NMR spectroscopic properties of these compounds. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.Russian Foundation for Basic Research, RFBR: 17-03-01029Deutscher Akademischer Austauschdienst, DAADMinistry of Education and Science of the Russian Federation, Minobrnauka: 4.6351.2017/8.9This work was supported by the Russian Ministry of Education and Science (State contract 4.6351.2017/8.9) and the Russian Foundation for Basic Research (grant 17-03-01029). Single crystal X-ray analysis of 23b was performed at the User Facilities Centers of IGIC RAS within the State Assignment on Fundamental Research to the Kurnakov Institute of General and Inorganic Chemistry. We thank the Deutscher Akademischer Austauschdienst DAAD for the financial support of the internship of S. D. at Clausthal University of Technology, Germany

Proof of concept for molecular velcro based on the attractive interaction between porphyrin and pyridine containing copolymers

In this short communication, we investigated the synthesis and mixing of porphyrin and pyridine functionalized copolymers as a proof of concept for a velcro-like interaction. A functionalized porphyrin monomer with one polymerizable side chain was synthesized following a rational synthetic pathway. Subsequent copolymerization and careful removal of residual free porphyrin led to poly(n-butyl acrylate-co-5,10,15-triphenyl-20-(3-vinylphenyl)porphyrin). The immobilized porphyrin was transformed into the corresponding zinc(II) complex, which is capable of the coordinative binding of one pyridine moiety. Complete metallation was proven by absorption spectroscopy. 4-Vinylpyridine was immobilized by copolymerization with n-butyl acrylate, too. Via controlled radical polymerization conditions, the molecular weight of poly(n-butyl acrylate-co-4-vinylpyridine) was limited to one tenth of the molecular weight of the porphyrin containing copolymer. This large difference in the molecular weight easily allowed identifying the polymers in the mixture of both. With the help of diffusion ordered nuclear magnetic resonance spectroscopy, the complete and temperature-stable precipitation of the porphyrin containing copolymer was observed, proving the expected attractive interaction and supramolecular network formation

Norbornadiene End-Capping of Cross-Coupling Polymerizations: A Facile Route to Triblock Polymers

The potential use of conjugated polymers in device applications is often limited by their less than optimal physicochemical properties. This work describes an efficient protocol to end-cap conjugated polymers synthesized via palladium-catalyzed cross-coupling polymerizations with norbornene groups. Specifically, the hydroarylation of norbornadiene is shown to be a high-yielding end-capping method. These strained bicyclic alkenyl end groups can be transformed into macroinitiators via ring-opening metathesis polymerization and can polymerize other strained monomers, such as norbornene, yielding elastomeric triblock copolymers.United States. Army Research Office (Contract W911NF-07-D-004)United States. Air Force Office of Scientific Research (FA9550-10-1-0395

Selective Michael-Aldol Reaction by use of Sterically Hindered Aluminum Aryloxides as Lewis Acids: An Easy Approach to Cyclobutane Amino Acids

(Chemical Equation Presented) A formal [2 + 2] cycloaddition of 2-amidoacrylates with monosubstituted donor olefins, including its asymmetric version, is described. The stereoselectivity of this reaction can be modulated by the use of sterically hindered aluminum aryloxides or methylaluminoxane as Lewis acids. The reaction was applied to the synthesis of both stereoisomers of 2-benzyloxycyclobutane--amino acid, which are protected serine analogues c4Ser(OBn). © 2005 American Chemical Society