Alkenyl iodonium triflates, preparation

Long-lived vinyl cations have been reviewed.114 Vinyl cations (67) can be prepared by the fragmentation of alkenyl(aryl)iodonium triflates, giving triflate capture products, some of which may be rearranged.115 Otherwise vinyl cation research has been quiet this year. 

Instead of silyl-, stannylalkenes are also suitable precursors [4] cyano phenyliodonium triflate (Section 9.1.4) was here the reagent of choice. This variation enabled the preparation of the parent ethenyl and several trisubstituted alkenyl phenyliodonium triflates [5], More elaborate members were obtained through additions to the triple bond of alkynyl iodonium salts, notably Diels-Alder adducts. 

The iodonium triflate (460 mg, 1 mmol) was added to a stirred slurry of anhydrous sodium p-toluene sulphinate (180 mg, 1.01 mmol) in dichloromethane (15 ml) at 20°C under nitrogen. After 15 min water (10 ml) was added and the phases were separated the aqueous layer was extracted with additional dichloromethane (2 x 5 ml), and the combined organic extracts were dried. The filtered solution was treated with hexanes (30 ml) and concentrated. The solid residue was purified by radial chromatography (silica gel, 200-400 mesh, dichloromethane-hexanes) to afford 3-tosyl-bicyclo[3.2.0]-3-heptene-2-one (197 mg, 75%), m.p. 164-165°C. The method is general for the preparation of sulphones with a cyclopentenone moiety other alkenyl iodonium salts gave alkynyl sulphones with sulphinates (Section 9.4.4). 

Similarly functionalized alkenyl(aryl)iodonium triflates 312 were prepared by the addition of (aryl)fluoroiodonium triflates 311 to terminal alkynes (Scheme 2.91) [45,48]. 

Several types of functionalized alkenyl(aryl)iodonium salts have been prepared by the addition of hyperva-lent iodine reagents to alkynes. Reactions of terminal alkynes with iodosylbenzene and triflic acid proceed as a highly stereoselective anti-addition to afford ( )-(P-trifluoromethanesulfonyloxyaIkenyl)phenyliodonium triflates 310 in high yield (Scheme 2.90) [446-448], Similar products were obtained Ifom the reactions of internal alkynes and parent acetylene [447],... 

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