1678-18-8Relevant articles and documents
ACYLATION OF PHOSPHORUS β-KETOYLIDES BY ACID CHLORIDES
Nesmeyanov, N. A.,Berman, S. T.,Rebrova, O. A.,Reutov, O. A.
, p. 181 - 183 (1982)
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Inner workings of a cinchona alkaloid catalyzed oxa-Michael cyclization: Evidence for a concerted hydrogen-bond-network mechanism
Hintermann, Lukas,Ackerstaff, Jens,Boeck, Florian
supporting information, p. 2311 - 2321 (2013/04/10)
Cinchona alkaloids catalyze the oxa-Michael cyclization of 4-(2-hydroxyphenyl)-2-butenoates to benzo-2,3-dihydrofuran-2-yl acetates and related substrates in up to 99 % yield and 91 % ee (ee=enantiomeric excess). Catalyst and substrate variation studies reveal an important role of the alkaloid hydroxy group in the reaction mechanism, but not in the sense of a hydrogen-bonding activation of the carbonyl group of the substrate as assumed by the Hiemstra-Wynberg mechanism of bifunctional catalysis. Deuterium labeling at C-2 of the substrate shows that addition of RO-H to the alkenoate occurs with syn diastereoselectivity of ≥99:1, suggesting a mechanism-based specificity. A concerted hydrogen-bond network mechanism is proposed, in which the alkaloid hydroxy group acts as a general acid in the protonation of the α-carbanionic center of the product enolate. The importance of concerted hydrogen-bond network mechanisms in organocatalytic reactions is discussed. The relative stereochemistry of protonation is proposed as analytical tool for detecting concerted addition mechanisms, as opposed to ionic 1,4-additions. Secret of cyclization: The cinchona alkaloid catalyzed asymmetric oxa-Michael cyclization of 2′-hydroxyphenyl-2-butenoates to benzodihydrofurans proceeds by a highly enantio- and diastereoselective syn-specific addition mode (see scheme). Transition-state activation of the carbonyl group by hydrogen bonding to the catalyst is excluded. This represents a clear-cut demonstration of the importance of concerted hydrogen-bond network mechanisms in cinchona-based asymmetric organocatalysis. Copyright
Synthesis of nitrogen heterocycles by intramolecular Michael type of amination via reduction of imines with di-n-butyliodotin hydride (n-Bu2SnIH)
Suwa, Toshihiro,Shibata, Ikuya,Nishino, Keita,Baba, Akio
, p. 1579 - 1581 (2008/02/10)
(matrix presented). Novel nitrogen heterocycles were prepared by a one-pot procedure involving the reductive amination of the bifunctional substrates containing an aldehyde and enone groups with di-n-butyliodotin hydride (n-Bu2SnIH).