- 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.
- Soleymani Movahed, Farzaneh,Foo, Siong Wan,Mori, Shogo,Ogawa, Saeko,Saito, Susumu
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p. 243 - 257
(2021/12/17)
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- Aerobic amide bond formation with N-hydroxysuccinimide
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Breathe easy: Molecular oxygen is one of the most abundant, atom-efficient, and economical oxidants. An aerobic oxidative amide formation from aldehydes and amines is reported. The method uses a catalytic amount of Co(OAc) 2 and N-hydroxysuccinimide as reaction promoters. It is applicable to chiral substrates without loss of their optical purity. Copyright
- Yao, Haoyi,Yamamoto, Kana
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supporting information; experimental part
p. 1542 - 1545
(2012/09/08)
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- A simple method removing 2-oxazolidinone and 2-hydroxyethylamine auxiliaries in methoxide-carbonate systems for synthesis of planar-chiral nicotinate
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A facile and practical removal of 2-oxazolidinone and 2-hydroxyethylamine auxiliaries was accomplished by treating the corresponding N-acyl-2-oxazolidinone and N-(2-hydroxyethyl)amide derivatives in simple methoxide-carbonate systems. The presence of excess DMC (dimethyl carbonate) accelerates the N-acyl bond cleavage for those substrates under mild reaction conditions, and the present method was found to be useful especially for the synthesis of planar-chiral nicotinate.
- Kanomata, Nobuhiro,Maruyama, Satoshi,Tomono, Katsuhito,Anada, Shinnosuke
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p. 3599 - 3603
(2007/10/03)
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