Fluorination of Aryl-Alkenyl-Iodonium Salts for Preparing Alkenyl Fluorides
Alkenyl fluorides are important building blocks for constructing fluoroalkene moiety containing complex organic molecules, which may possess interesting biological activities and thus are particularly attractive to the pharmaceutical and agrochemical industries [1, 2, 3]. In addition, they can be used as monomers for polymerization and copolymerization to form fluoropolymers with certain special properties [4, 5, 6]. Numerous synthetic approaches have been developed to obtain selectively functionalized alkenyl fluorides which can be classified into five major categories based upon the organic reactions: (1) Horner-Wadsworth-Emmons, Horner-Wittig, Julia, Peterson, and Reformatsky-type olefination reactions, (2) hydrofluorination of alkynes, (3) electronic fluorination of alkenyl metals, (4) reductive elimination reaction of multi-halo compounds, and (5) various metal catalyzed cross-coupling reactions using fluoroalkenyl moiety containing synthons, etc. These synthetic methods have been summarized in several reviews and book chapters from different perspectives [1, 2, 3, 7, 8, 9, 10, 11, 12].
In recent years, the development of hypervalent iodonium salts has played an important role in organofluorination and radiofluorination, especially in the development of new radiopharmaceutical and molecular imaging agents [13, 14, 15]. The synthetic methods for multifunctionalized alkenyl fluorides using aryl-alkenyl-iodonium salts as intermediates have been established over the last two decades. A summary of these synthetic methods, which offer several advantages, including mild reaction conditions, good reaction yields, access to a variety of functional groups, as well as high stereoselectivity, is given in the following paragraphs.
Synthesis of Multifunctionalized Fluoroalkenes Via Aryl-Alkenyl-Iodonium Salt Intermediates
After exploration over two decades, fluoroalkenyliodonium salts have developed into sophisticated synthons for synthesizing complex organic molecules containing an alkenyl fluoride moiety. The related synthetic methods demonstrate many advantages, such as mild reaction conditions, good reaction yields, high stereoselectivity, as well as the flexibility of combination with various metal-catalyzed cross-coupling reactions to synthesize multifunctionalized polyenes. There is no doubt that more applications will be found in pharmaceutical, agrochemical, and material science research.
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