Electrophile-Induced Cyclization/Migration Reaction for the Synthesis of 2,3-Dihydro-5-iodopyran-4-one Shu-Guang Wen, †,‡ Wei-Min Liu, † and Yong-Min Liang* ,†,§ State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Science, Lanzhou 730000, People’s Republic of China, Graduate School of Chinese Academy of Science, Beijing 100039, People’s Republic of China, and State Key Laboratory of Applied Organic Chemistry, Lanzhou UniVersity, Lanzhou 730000, People’s Republic of China liangym@lzu.edu.cn ReceiVed March 12, 2008 A novel method for the construction of 2,3-dihydro-5- iodopyran-4-one through a domino cyclization/migration reaction of 1-alkynyl-2,3-epoxy alcohol was developed. Wet solvent is essential for this reaction. The resulting iodine- containing product can be readily elaborated to more complex products by using known organopalladium chemistry. Semipinacol rearrangement is a powerful means of creating a new carbon-carbon bond, frequently with high stereocontrol. 1 It has found wide application in the construct of various structures, such as stereodefined mono- and disubstituted aldol adducts, 2 diols, 3 ketones, 4 ring-expanded 5 and ring-contracted 6 products, -amino ketones, 7 and -halo ketones. 8 Furthermore, some more complex structures could be synthesized through the application in a tandem reaction. 9 Despite this, most of these reactions are catalyzed by Lewis acid and the reaction induced by a π-activator is rare. Electrophilic cyclization has emerged as an important topic in organic chemistry. 10 Many kinds of heterocycles and car- bocycles can be constructed by this method. The electrophile has been proven to be very reactive to the unsaturated bond. Recently Kirsch has reported an interesting tandem reaction for the synthesis of 4-iodo-3-furanone from 2-alkynyl-2-silyloxy carbonyl compounds. 11 This reaction was believed to combine the process of a heterocyclization with a 1,2-alkyl shift. As part of our program of electrophile induced reaction, 12 we envisioned that 2,3-dihydro-5-iodopyran-4-one would be produced from the iodo-induced semipinacol reaction of 1-alkynyl-2,3-epoxy al- cohol (eq 1). In this paper, we will report our results. The epoxide alcohol 1a was synthesized and the reaction was examined under various conditions (Table 1). The reaction was initially examined with 3 equiv of I 2 as the electrophile in the presence of 3 equiv of NaHCO 3 in CH 3 CN at 0 °C for 12 h (entry 1). The expected rearrangement product 2a was produced in 60% yield and the enone 3a was isolated in 23% yield. 13 No reaction was detected with NIS as the reagent. Then ICl was tested in dry CH 3 CN and no reaction occurred. 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