title: (16) O/(18) O Exchange of Aldehydes and Ketones caused by H2 (18) O in the Mechanistic Investigation of Organocatalyzed Michael, Mannich, and Aldol Reactions.
abstract: Organocatalyzed Michael, Mannich, and aldol reactions of aldehydes or ketones, as nucleophiles, have triggered several discussions regarding their reaction mechanism. H2 (18) O has been utilized to determine if the reaction proceeds through an enamine or enol mechanism by monitoring the ratio of (18) O incorporated into the final product. In this communication, we describe the risk of H2 (18) O as an evaluation tool for this mechanistic investigation. We have demonstrated that exchange of (16) O/(18) O occurs in the aldehyde or ketone starting material, caused by the presence of H2 (18) O and amine catalysts, before the Michael, Mannich, and aldol reactions proceed. Because the newly generated (18) O starting aldehydes or ketones and (16) O water affect the incorporation ratio of (18) O in the final product, the use of H2 (18) O would not be appropriate to distinguish the mechanism of these organocatalyzed reactions.
authors: Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza, Aoba-ku, Sendai, 980-8578, Japan. yhayashi@m.tohoku.ac.jp.|Department of Industrial Chemistry, Faculty of Engineering, Tokyo University of Science, Kagurazaka, Shinjuku-ku, Tokyo, 162-8601, Japan. yhayashi@m.tohoku.ac.jp.
authors: Yujiro
authors: Y
authors: Hayashi
authors: Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza, Aoba-ku, Sendai, 980-8578, Japan.
authors: Takasuke
authors: T
authors: Mukaiyama
authors: Department of Industrial Chemistry, Faculty of Engineering, Tokyo University of Science, Kagurazaka, Shinjuku-ku, Tokyo, 162-8601, Japan.
authors: Meryem
authors: M
authors: Benohoud
authors: Department of Industrial Chemistry, Faculty of Engineering, Tokyo University of Science, Kagurazaka, Shinjuku-ku, Tokyo, 162-8601, Japan.
authors: Nishant R
authors: NR
authors: Gupta
authors: Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza, Aoba-ku, Sendai, 980-8578, Japan.
authors: Tsuyoshi
authors: T
authors: Ono
authors: Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza, Aoba-ku, Sendai, 980-8578, Japan.
authors: Shunsuke
authors: S
authors: Toda
keywords: asymmetric synthesis; enamines; enols; organocatalyst; reaction mechanisms