- Phosphorus-Based Organocatalysis for the Dehydrative Cyclization of N-(2-Hydroxyethyl)amides into 2-Oxazolines
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A metal-free, biomimetic catalytic protocol for the cyclization of N-(2-hydroxyethyl)amides to the corresponding 2-oxazolines (4,5-dihydrooxazoles), promoted by the 1,3,5,2,4,6-triazatriphosphorine (TAP)-derived organocatalyst tris(o-phenylenedioxy)cyclotriphosphazene (TAP-1) has been developed. This approach requires less precatalyst compared to the reported relevant systems, with respect to the phosphorus atom (the maximum turnover number (TON) ～30), and exhibits a broader substrate scope and higher functional-group tolerance, providing the functionalized 2-oxazolines with retention of the configuration at the C(4) stereogenic center of the 2-oxazolines. Widely accessible β-amino alcohols can be used in this approach, and the cyclization of N-(2-hydroxyethyl)amides provides the desired 2-oxazolines in up to 99% yield. The mechanism of the reaction was studied by monitoring the reaction using spectral and analytical methods, whereby an 18O-labeling experiment furnished valuable insights. The initial step involves a stoichiometric reaction between the substrate and TAP-1, which leads to the in situ generation of the catalyst, a catechol cyclic phosphate, as well as to a pyrocatechol phosphate and two possible active intermediates. The dehydrative cyclization was also successfully conducted on the gram scale.
- Foo, Siong Wan,Mori, Shogo,Ogawa, Saeko,Saito, Susumu,Soleymani Movahed, Farzaneh
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supporting information
(2021/12/17)
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- Controlled/living ring-opening polymerization of ε-caprolactone catalyzed by phosphoric acid
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The bulk ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) by various phosphoric acids using phenylmethanol as the initiator was conducted. 1,1'-bi-2-Naphthol (BINOL)-based phosphoric acid was found to be an effective organocatalyst for ROP leading to polyesters at 90°C. The overall conversion to poly(ε-caprolactone) was more than 96% and poly(ε-caprolactone) with Mw of 8400 and polydispersity index of 1.13 was obtained. 1H NMR spectra of oligomers demonstrated the quantitative incorporation of the protic initiator in the polymer chains and showed that transesterification reactions did not occur to a significant extent. The controlled polymerization was indicated by the linear relationships between the number- average molar mass and monomer conversion or monomer-to-initiator ratio. In addition, the present protocol provided an easy-to-handle, inexpensive and environmentally benign entry for the synthesis of biodegradable materials as well as polyesters for biomedical applications. Science China Press and Springer-Verlag Berlin Heidelberg 2012.
- Chen, Chun Xia,Xu, Rong,Li, Bin
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p. 1257 - 1262
(2012/11/13)
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- PYROCATECHOL CYCLOPHOSPHATES IN REACTIONS WITH PROTON-CONTAINING NUCLEOPHILES
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A general principle of the hydrolysis and alcoholysis of cyclophosphates of pyrocatechol and its derivatives is facile ring opening and anomalously facile cleavage of the P-O (P-N) bond to give, in all of the indicated cases, phosphoric acid 2-hydroxyphenyl phosphate.The latter is predetermined by the formation of a hydrogen bond with the participation of the phenolic hydroxy group of the 2-hydroxyphenyl radical.
- Nifant'ev, E. E.,Kukhareva, T. S.,Soldatova, I. A.,Matrosov, E. I.
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p. 1209 - 1212
(2007/10/02)
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- Organophosphorus Antioxidants. II. Kinetics and Mechanism of the Decomposition of Alkylhydroperoxides by Esteramides of Phosphorous and Phosphoric Acid
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The reaction mechanism of 2-amido-1,3,2-benzodioxaphospholes (1) with cumyl and t-butylhydroperoxide has been studied kinetically by means of 31P-n.m.r. and e.p.r. spectroscopy and high pressure liquid chromatography. 1 reacts with cumyl hydroperoxide to give the corresponding 2-oxides (2) which with more hydroperoxide and/or water form the phosphate esters 7 and 8.These acidic phosphates decompose cumyl hydroperoxide catalytically giving phenol and aceton.All amides (1) react with t-butyl hydroperoxide stoichiometrically to give t-butanol.The ionic mechanism of hydroperoxide decomposition is accompanied in a minor proportion by a homolytical one.
- Rueger, C.,Arnold, D.,Schwetlick, K.
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p. 706 - 716
(2007/10/02)
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