Alkenyl iodonium salts

Other pseudo-halides are used for carbonylation. Phenyl tluorosulfonate (484) can be carbonylated to give benzoate[337]. Aryl(aryl)iodonium salts[338], aryl(alkenyl)iodonium salts (485)[339], and arylialkynyl)iodonium salts (486)[340] are reactive compounds and undergo carbonylation under mild conditions (room temperature, 1 atm) to give aryl, alkenyl, and alkynyl esters. lodoxybenzene (487) is carbonylated under mild conditions in... 

Evidence for a Michael addition of a nucleophile to alkenyl(phenyl)iodonium salts at the Cp atom has now been reported for the first time. Nucleophilic vinylic substitutions of (Z)-(/3-bromoalkenyl)iodonium tetrafiuoroborates (161) and its (Z)-(/3-chloroalkenyl) analogue with sodium benzenesulfinate in THE afforded stereoselectively (Z)-l,2-bis(benzenesulfonyl)alkene (163) with retention of configuration. Intermediate formation of (Z)-[/3-(benzenesulfonyl)alkenyl]iodonium salt (162) in these reactions was established by NMR experiments in CDCI3. The formation of (Z)-(162) involves a hitherto unobserved Michael addition of benzenesulfinate anion to the alkenyliodonium salts at the Cp atom, followed by halogen extrusion. ... 

An interesting lactonization of 4- or 5-alkynoic acids with concomitant formation of alkenyl iodonium salts occurred on treatment of the acids with iodosylbenzene-boron trifluoride [8] ... 

The exceptional nucleofugality of the phenyliodonio group has been determined in an alkenyl salt and it is about 106 times greater than that of triflate [30]. This remarkable property makes alkenyl iodonium salts excellent vinyl cation equivalents in nucleophilic substitutions. The chemistry of alkenyl iodonium salts is dominated by the transfer of their aliphatic moiety to a variety of nucleophiles other important reactions involve Michael-type addition and alkylidenecarbene generation, along with elimination to alkynes which is actually an undesirable side-reaction. 

Selected alkenylations with phenyl alkenyl iodonium salts... 

Simple and phenylated alkynes were prepared from alkenyl iodonium salts and lithium organocuprates. 

Phenylation, by using diphenyl lithium cuprate, was stereospecific in both E and Z isomers of appropriate alkenyl iodonium salt, proceeding with complete retention of configuration. 

Synthetic methods for the preparation of dienes and enynes abound, yet the use of alkenyl iodonium salts offers distinct advantages. Their coupling reactions with electron-deficient alkenes and alkenyl- or alkynylstannanes constitute a valuable extension to the previously existing methodology, because of mild conditions, ease of operation, high stereoselectivity and good yields. The simplest reaction of this category is with unsaturated carbonyl compounds and requires palladium catalysis. 

Other alkenyl iodonium salts which furnished functionalized dienes had a cyclo-hexenyl, a 2-(tosyloxy)hexenyl or a tosyloxyvinyl moiety the unsaturated partners included propenal, methyl acrylate and styrene. The yields were consistently high (64-85%) and the stereoselectivity invariably trans. An alternative method for the synthesis of dienes involved alkenyl stannanes such as CH2=CHSnBu3, E-PhCH=CHCH2SnBu3 and CH2=CHCH2SnBu3 [38]. Several alkynylstannanes afforded similarly enynes in good yield [39]. 

Alkylidenecarbenes gave methylenecyclopropanes with alkenes, as exemplified in the reaction of a simple alkenyl iodonium salt with styrene [43] ... 

An addition-elimination sequence was proposed for the intramolecular aromatic cyclization of a series of 4-aryl-alkenyl iodonium salts which were converted into dihydronaphthalenes [44] ... 

Whereas oxygen nucleophiles gave poor yields of alkenylated products with alkenyl iodonium salts, the reactions with sulphur nucleophiles proceeded more efficiently, leading to unsaturated sulphides and sulphones. Thus, 4-t-butylcyclohexenyl phenyliodonium salts afforded with sodium thiophenoxide 4-t-butylcyclohexenyl phenyl sulphide (81%) [3] and with sodium phenylsulphinate the corresponding sulphone (29%) in the presence of 18-crown-6, the yield of the latter rose to 80% [45]. jS-Phenylsulphonylalkenyl iodonium salts with sodium phenylsulphinate at 0°C, without any catalyst, afforded Z-l,2-bis(phenylsulphonyl)alkenes, in high yield with retention of the stereochemistry [45] ... 

The substitution of alkenyl iodonium salts by halides, using tetrabutylammonium salts, has been studied (Table 9.2). Exclusive inversion of configuration occurred in acetonitrile, so that -precursors gave solely Z-haloalkenes in high yield [35]. In marked contrast, complete retention occurred with cuprous and potassium halides in dichloromethane. Retention of configuration was also noted in reactions of / -substituted alkenyl iodonium salts for example, from /J-phenylsulphonyl decenyl phenyliodonium ion, cis products were formed exclusively in high yield [34],... 

These highly reactive yet stable species are strong electrophiles of tetraphilic character, since nucleophiles may attack three different carbon atoms (a,/ ,a ) and iodine. In most reactions the first step is a Michael addition at fi-C with formation of an alkenyl zwitterionic intermediate (ylide) which normally eliminates iodoben-zene, generating an alkylidene carbene then, a 1,2-shift of the nucleophile ensues. The final result is its combination with the alkynyl moiety which behaves formally as an alkynyl cation. The initial adduct may react with an electrophile, notably a proton, in which case alkenyl iodonium salts are obtained also, cyclopentenes may be formed by intramolecular C-H 1,5-insertion from the alkylidenecarbenes ... 

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). 

Pirguliyev, N. S., Brel, V. K., Zefirov, N. S., Stang, P. J. Stereoselective synthesis of conjugated alkenynes via palladium-catalyzed coupling of alkenyl iodonium salts with terminal alkynes. Tetrahedron 1999, 55, 12377-12386. 

As discussed in the previous sections, the thermal solvolysis reactions of alkenyl iodonium salts usually occur via trans j8-phenyl- or trans j8-alkyl-assisted departure of the iodobenzene leaving group, by in-plane vinylic Sn2 substitution or by ligand... 

Moriarty, R.M., Epa, W.R. and Awasthi, A.K. (1991) Palladium-catalyzed coupling of alkenyl iodonium salts with olefins a mild and stereoselective Heck-type reaction using hypervalent iodine. J. Am. Chem. Soc., 113, 6315-7. 

Cross-Coupling Reaction Using 2-Fluoro-l -halo-1 -alkenes or (2-Fluoro-l-alkenyl)iodonium Salts... 

Both ( )- and (Z)-(2-fluoro-l-alkenyl)iodonium salt 55 (X = I Ar) can be prepared stereoselectively. ( )-(2-Fluoro-l-dodecyl)iodonium salt 55b is prepared by the addition of iodoarene difluoride to 1-dodecyne [84, 85]. On the other hand, (Z)-55b was prepared from the l-dodecynyUodonium salt by a reaction with aqueous HF [86] or metal fluoride [87, 88] (Scheme 25). 

Scheme 25 Stereoselective synthesis of ( )- and (Z)-(2-fluoro-l-alkenyl)iodonium salt 55b...

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