Metal Catalyzed Synthetic Reactions via Aerobic Oxidation as a Key Step
New aerobic oxidative metal catalyzed synthetic reactions are described: The Cu(II) complex catalyzed the acylation of thioester in Wittig lactonization under neutral conditions and the dissymmetrization of symmetric dithiomalonates via selective monoacyl
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Abstract New aerobic oxidative metal catalyzed synthetic reactions are described: The Cu(II) complex catalyzed the acylation of thioester in Wittig lactonization under neutral conditions and the dissymmetrization of symmetric dithiomalonates via selective monoacylation. The key step in this reaction was the formation of an acylketene, the stability of which would contribute to selectivity. The aerobic Rh/C-catalyzed oxidative homo- and cross-coupling of aryl amines was developed. The coupling reactions afforded symmetrical and nonsymmetrical biaryl amines in excellent yields. These reactions provide a mild, operationally simple, and efficient approach for the synthesis of biaryls which are important to pharmaceutical and materials chemistry.
Keywords Aerobic oxidation Metal catalysts Heterogeneous catalysts Recyclable
Acylation
Coupling
1 Introduction Metal-catalyzed reactions are one of the main topics in synthetic organic chemistry and process chemistry. Needless to say, numerous metal-catalyzed reactions have achieved highly efficient C–C, C–O, and C−heteroatom bond formations. Oxidative (or oxidation) reactions are frequently used in not only functional group transformation but also C–C or C–O bond formation along with C–H bond cleavage (oxidative coupling). In the oxidative metal-catalyzed reactions, if air or oxygen is an oxidant, usage of hazardous peroxides or toxic high valence metals can be M. Shindo (&) Institute for Materials Chemistry and Engineering, Kyushu University, 6-1 Kasugako-en, Kasuga, Fukuoka 816-8580, Japan e-mail: [email protected] K. Matsumoto Faculty of Pharmaceutical Sciences, Tokushima Bunri University, 180 Nishihama-Boji, Yamashiro-cho, Tokushima 770-8514, Japan © Springer Nature Singapore Pte Ltd. 2017 K. Tomioka et al. (eds.), New Horizons of Process Chemistry, DOI 10.1007/978-981-10-3421-3_2
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avoided. In terms of green chemistry as well as practical synthesis, aerobic conditions would be favorable. Furthermore, reaction control would be more easily accomplished under aerobic conditions than inert gas atmosphere. In this chapter, we describe our recent results on aerobic Cu(II) catalyzed acylation, in which catalyst deactivator is eliminated by oxidation, and aerobic metal catalyzed oxidative coupling reactions.
2 Aerobic Cu-Catalyzed Acylation-Wittig Reaction Under Neutral Conditions 2.1
Acylation-Wittig Reaction Under Neutral Conditions
During the course of our synthesis of xanthanolide sesquiterpenoids [1, 2], we found one-pot acylation-Wittig lactonization of acyloins (Fig. 1). A mixture of the acyloin 1 (a-hydroxy-cyclic hemiacetal as its equivalent) and excess amount of Wittig reagent 2 was heated in xylene at 150 °C to form a butenolide 3 in excellent yield. When the ester moiety was replaced to more acidic eliminating group like thiophenol, the reaction was fairly accelerated, albeit under harsh conditions (Fig. 2). These results indicated a reaction mechanism of the initial rate-determining acylation and the fol
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