1485-07-0Relevant articles and documents
Conversion of thioureas to fluorescent isothiouronium-based photoinduced electron transfer sensors for oxoanion sensing
Nishizawa, Seiichi,Cui, Ying-Yu,Minagawa, Masakazu,Morita, Kotaro,Kato, Yuichi,Taniguchi, Shinichiro,Kato, Ryo,Teramae, Norio
, p. 866 - 870 (2002)
A convenient conversion is described of thiourea-based receptors to fluorescent isothiouronium-based photoinduced electron transfer (PET) sensors for oxoanion sensing. Naphthalene- or anthracene-functionalized mono-isothiouroniums are synthesized from the corresponding thioureas, in which the fluorophore is connected to the sulfur atom of the thiourea moiety by a methylene or an ethylene spacer. Even though all of the isothiouroniums with a methylene spacer readily decompose in MeOH upon excitation of the fluorophore moiety, the isothiouronium with an ethylene spacer shows good stability under identical conditions. The naphthyl isothiouronium with an ethylene spacer shows a significant fluorescence enhancement upon formation of a 1 : 1 complex with oxoanions in MeOH, and the selectivity follows the order of hydrogen phosphate > acetate ? dihydrogen phosphate ? chloride. The results in the present work indicate that various types of fluorescent PET sensors might be readily obtainable from non-fluorescent thiourea-based receptors by the introduction of appropriate fluorophores at the sulfur atom of thiourea-binding sites.
INTER- AND INTRA-MOLECULAR PHOTOCYCLOADDITION OF ENOL ETHERS TO NAPHTHALENE
Gilbert, Andrew,Heath, Peter,Kashoulis-Koupparis, Annoula,Ellis-Davies, Graham C. R.,Firth, Susan M.
, p. 31 - 36 (1988)
The isomeric non-conjugated naphthyl enol ether bichromophores (6) and (7) display markedly different photoreactivities.The former undergoes ? + 2?> cycloaddition from the S1 state whereas the latter is relatively photostable.The two cyano derivatives (4) and (5) both yield intramolecular cycloadducts but the orientation of the addition is the opposite of that predicted from the reported intermolecular cyanonaphthalene-enol ether photoreactions. 2,3-Dihydrofuran undergoes specific "head to head" endo photoaddition to naphthalene but in contrast the major adducts from 2,3-dihydrofuran and this arene have "head to head" exo and "head to tail" endo structures.The adduct (18) undergoes a facile 1,3-shift to yield the (4? + 2?) endo adduct (19).The reactivities of the bichromophores and the regiochemistries of the additions are considered in relation to the relative charge densities at the 1- and 2-positions of the S1 arene.
Bidentate Lewis acids for the activation of 1,2-diazines - A new mode of catalysis
Kessler, Simon N.,Neuburger, Markus,Wegner, Hermann A.
, p. 3238 - 3245 (2011)
Bidentate Lewis acids were applied as catalysts for the inverse-electron-demand Diels-Alder (IEDDA) reaction of 1,2-diazines. The concept of catalysis is based on the coordination of the bidentate Lewis acid to both nitrogen atoms of the 1,2-diazine moiety, thereby reducing the electron density and lowering the energy of the LUMO. This should, according to frontier molecular orbital (FMO) theory, facilitate the cycloaddition step. This new concept was successfully applied to a variety of dienophiles and substituted phthalazine substrates. Careful investigations of the mechanism led to the isolation and characterization of key intermediates; all of which support the presented catalytic cycle. Copyright
An air-stable bisboron complex: A practical bidentate Lewis acid catalyst
Hong, Longcheng,Ahles, Sebastian,Heindl, Andreas H.,Tiétcha, Gastelle,Petrov, Andrey,Lu, Zhenpin,Logemann, Christian,Wegner, Hermann A.
, p. 618 - 625 (2018)
We report an air-stable bisboron complex as an efficient catalyst for the inverse electron-demand Diels-Alder (IEDDA) reaction of 1, 2-diazine as well as 1, 2, 4, 5-tetrazine. Its stability towards air and moisture was demonstrated by NMR studies enabling its application in organic transformations without glovebox. A one-pot procedure for its synthesis was developed starting from 1, 2-bis(trimethylsilyl) benzene greatly enhancing its practicality. Comparative reactions were carried out to evaluate its catalytic activity in IEDDA reactions of diazine including phthalazine as well as 1, 2, 4, 5-tetrazine.
Chromium-Catalyzed Borylative Coupling of Aliphatic Bromides with Pinacolborane by Hydrogen Evolution
Fu, Aiping,Li, Chao,Luo, Meiming,Zeng, Xiaoming,Zhao, Lixing
supporting information, p. 2204 - 2208 (2021/06/28)
The chromium-catalyzed borylative coupling between aliphatic bromides and pinacolborane (HBpin) is described. This reaction was promoted by low-cost and bench-stable CrCl3as a precatalyst combined with 4,4′-di-tert-butyl-2,2′-dipyridyl and aluminum, presenting a rare example of using HBpin as a borane reagent by coupling with alkyl bromides in forming borylated alkanes. Mechanistic studies indicate that aluminum plays important roles in the formation of reactive Cr species and aliphatic radicals, which lead to (alkyl)Cr by reaction with HBpin to give the products.
Allyl 4-Chlorophenyl Sulfone as a Versatile 1,1-Synthon for Sequential α-Alkylation/Cobalt-Catalyzed Allylic Substitution
Kojima, Masahiro,Matsunaga, Shigeki
, p. 1934 - 1946 (2020/07/03)
Despite their unique potential as rare 1,1-dipole synthons, allyl sulfones are rarely used in target-oriented syntheses, likely due to the lack of a general catalytic method for their branch-selective allylic substitution. Herein, we identified allyl 4-chlorophenyl sulfone as a versatile linchpin for both base-mediated α-derivatization and subsequent cobalt-catalyzed allylic substitution. The sequential transformations allow for highly regioselective access to branched allylic substitution products with a variety of aliphatic side chains. The photoredox-enabled cobalt catalysis is indispensable for achieving high yields and regioselectivity for the desulfonylative substitution in contrast to traditional metal-catalyzed protocols, which lead to inferior outcomes in the corresponding transformations.
