Metalation of Azoles and Related Five-Membered Ring Heterocycles
-T. L.S. KishbaughMetalation of Pyrrole-K.-S. YeungFurans and Benzofurans -P. E. AlfordLithiation-Based and Magnesation-Based Strategies for the Functionalization of Imidazole: 2001–2010 -L. FuMetalation of Oxazoles and Benzoxazoles -S
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Furans and Benzofurans Kap-Sun Yeung
Abstract This chapter reviews the significant developments in the metalation of furans and benzofurans and applications of the resulting metalated species in the past decade. New and interesting metalated furan and benzofuran derivatives and their novel reactions are featured. Topics encompass lithiation, magnesation and zincation, the use of boronated and other metalated furans and benzofurans in crosscoupling reactions, as well as the use of metalated furans and benzofurans in addition reactions. Examples of regioselective metalation are highlighted, and metalation of related furo heterocycles is also summarized. Keywords Addition reactions Benzofurans Cross-coupling Furans Metalation
Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Lithiation of Furans and Benzofurans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Magnesation of Furans and Benzofurans, and Their Applications . . . . . . . . . . . . . . . . . . . . . . . . . 4 Zincation of Furans and Benzofurans, and Their Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Boronated Furans and Benzofurans in Cross-Coupling Reactions . . . . . . . . . . . . . . . . . . . . . . . . . 6 Other Metalated Furans and Benzofurans in Cross-Coupling Reactions . . . . . . . . . . . . . . . . . . . 7 Regioselective Functionalization of Poly-halogenated Furans and Benzofurans . . . . . . . . . . 8 Metalated Furans and Benzofurans in Addition Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Lithiation of Related Furo Heterocycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
K.-S. Yeung (*) Bristol-Myers Squibb Research and Development, 5 Research Parkway, P.O. Box 5100, Wallingford, CT 06492, USA e-mail: [email protected]
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K.-S. Yeung
1 Introduction Furan and benzofuran are common structural elements present in numerous bioactive natural products as well as pharmaceuticals, molecular electronic and functional polymers [1]. Recent noteworthy examples from natural sources, as shown in Fig. 1, include the cytotoxic diterpenoid salvileucalin B [2] and the selective phosphoinositide-3-kinase a inhibitor liphagal [3]. The total syntheses of both of these unusual molecular structures have recently been accomplished [3, 4]. Due to their electron-rich character, furans also function as versatile precursors to a variety of functional moieties as well as carbocycles and heterocycles through the transformation of the furan nucleus, for example, by oxidation and cycloaddition reactions [5–7]. A broadly employe
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