Activation of ketene silyl acetals by 10-methylacridinium perchlorate: a novel catalysis in mukaiyama reaction

Junzo Otera, Yoshiyuki Wakahara, Hidenobu Kamei, Tsuneo Sato, Hitosi Nozaki, Shinichi Fukuzumi

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10-Methylacridinium perchlorate (1) effectively promotes various reactions of ketene silyl acetals: aldol and Michael addition products are obtained with aldehydes, ketones, acetals, and α-enones. The reactions exhibit unusual dependency upon 1, namely the yields are excellent when a catalytic amount of 1 is employed whereas no desired products are accessible by the use of 1 in a stoichiometric quantity. A novel catalytic cycle is proposed.

Original languageEnglish
Pages (from-to)2405-2408
Number of pages4
JournalTetrahedron Letters
Issue number21
StatePublished - 20 May 1991

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with the unchanged ketene silyl acetal. In other words, one of the reactantss erves as a precursor of the catalyst. Since the alkylation of 1 precedes the aldol or Michael reaction, the use of an equivalent amount of this compounds completely consumes the ketene silyl acetal which otherwise should be supplied to the reaction with an electrophile. The remarkablee ffect of the dosage of 1 is apparent on this basis. The reasons for lower yields with 2b and 2c are two-fold. First, the rate of alkylation of 1 is slower than that of 2a as is seen from the results in Scheme 1. Secondly, 2b and 2c themselves are less reactivet han 2a in the Mukaiyama reactions.7) In summary, 1 has proved to work as an efficient activator of ketene silyl acetals. Due to the neutral and air-stable properties, 1 would find versatile synthetic applications, especially for aldol and Michael products bearing quaternary carbons. In a strict sense, “catalyst” is regarded as a substance which reduces the activation energy but hardly affects equilibrium of the reaction. Consequently, the catalyst is not involved in the stoichiometty of the reactants and products. However, this sense is violated frequently and the extreme case is “auto-catalysis” where one of the reaction products catalyzes the reaction through which the catalyst itself has been produced. The novel catalysis presented in this paper constitutes the opposite extreme where one of the reactantsi s forced to react by the self-createdc atalyst. Acknowledgment. This work was partially supported by Grant-in-Aid from The Ministry of Education, Science, and Culture, Japan.


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