Phenyl alkenyl iodonium salts

Selected alkenylations with phenyl 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. ... 

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. 

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] ... 

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... 

The alkenyl(phenyl) iodonium salt 725 undergoes the facile cross-coupling with vinylstannane to form the conjugated diene 726[594]. 

There are two approaches for the preparation of alkenyl(phenyl)iodonium salts reaction of an activated alkene with an iodine(III) species and addition to a triple bond, either of simple alkynes or of alkynyl(phenyl)iodonium salts. 

Other similar approaches have used alkenylsilanes and PhI0/Et30+ BF4 and also alkenylstannanes and PhI+CN TfO [123,124]. The reactions proceed also stereoselectively. The parent ethenyl(phenyl)iodonium triflate as well as several trisubstituted alkenyl members were obtained in this way. In an analogous manner E-alkenylzirconium compounds upon reaction with (diacetoxyiodo)ben-zene afforded -alkenyl(phenyl)iodonium salts stereoselectively [125]. 

Alkynyl(phenyl)iodonium salts are transformed into their functionalized alkenyl analogs by reactions involving addition of nucleophiles to their triple bond which is a strong Michael acceptor. In most of them the stereochemistry is normally Z (Scheme 41). The choice of solvent, e.g. methanol, is crucial in some cases for the exclusive and almost quantitative formation of the Z-product... 

Electrophilic addition of iodine(III) reagents to the triple bond of alkynes leading to alkenyl(phenyl)iodonium salts is also possible. It has been effected in some alkynes, including acetylene, with Phl+F TfO" [95] or PhI+OH TfO [129] or Phi and XeF2 in MeS03H [130] to afford 2- -trifyloxy-alkenyl(phenyl)iodo-nium salts. Terminal alkynes reacted with p-TolylIF2 in Et3N-5HF to afford similarly jS-E-fluoroalkenyl(phenyl)iodonium fluorides (Scheme 43) [131]. 

More conventional additions to alkynyl(phenyl)iodonium salts which served as dienophiles or dipolarophiles have led to a variety of alkenyl(phenyl)iodo-nium salts as exemplified in Scheme 44 [132,133]. 

Alkenyl(phenyl)iodonium salts have attracted a significant interest recently as stable and readily available powerful alkenylating reagents. Several convenient, general procedures for the stereoselective synthesis of alkenyliodonium salts from silylated or stannylated alkenes and the appropriate hypervalent iodine reagents are known [5]. The chemistry of alkenyliodonium salts has been extensively covered in several recent reviews [42 - 45]. 

Numerous reactions of alkenyl(phenyl)iodonium salts leading to the formation of new C-C bond have been reported in the literature. The most important and synthetically useful reactions include the generation and subsequent cyclization of alkylidenecarbenes, alkenylation of carbon substrates via nucleophilic vinylic substitution, and transition metal-mediated coupling reactions. 

Alkenyl(phenyl)iodonium salts are highly reactive in vinylic nucleophilic substitution reactions because of the excellent leaving group ability of the phenyliodonium moiety. Only a few examples of non-catalytic alkenylation of carbon nucleophiles are known [50,51]. In most cases these reactions proceed with predominant retention of configuration via the addition-elimination mechanism or ligand coupling on the iodine [42,50]. 

Enolate anions derived from various 1,3-dicarbonyl compounds can be viny-lated with cyclohexenyl- and cyclopentenyl- iodonium salts (Scheme 27) [50]. The vinylation of enolate anions 58 in these reactions is frequently accompanied by the formation of the phenylated dicarbonyl compounds however, the selectivity of these vinylations can be improved by using alkenyl(p-methoxyphenyl)-iodonium salts instead of 57. 

The palladium/copper-cocatalyzed coupling of the readily available trisubsti-tuted alkenyl(phenyl)iodonium triflates 77 with alkynyl- and alkenylstannanes proceeds under exceedingly mild conditions with retention of geometry of the alkenyl ligand of the iodonium salt (Scheme 35) [60]. 

Alkenyl(phenyl)iodonium salt Alkenyl, allyl D [163]... 

Phenyi(cyano)iodine(III) tosylale. Alkenyl(phenyl)iodonium salts. 

Alkenyl(phenyl)iodonium salts. These salts are prepared from alkenylstan-nanes by reaction with PhI(CN)OTs in CH2CI2 at —23°C. 

Preparation First representatives of alkenyliodonium salts, dichlorovinyl(phenyl)iodonium species, were reported by Thiele and Haakh in the early 1900s [436]. The first general synthetic approach to alkenyl(phenyl)iodonium salts was developed by Ochiai in the mid-1980s [437,438], This method is based on the reaction of silylated alkenes 299 with iodosylbenzene in the presence of Lewis acids, leading to the stereoselective formation of various alkenyliodonium tetrafluoroborates 300 in good yield (Scheme 2.85). 

Likewise, the reaction of vinylzirconium derivatives 305 with (diacetoxyiodo)benzene followed by anion exchange affords alkenyl(phenyl)iodonium salts 306 stereoselectively with retention of configuration (Scheme 2.88) [442]. 

Alkynyl(aryl)iodonium salts can serve as precursors to some alkenyl(aryl)iodonium salts [453 55], For example, ( )-(3-fluoroalkenyl(phenyl)iodonium tetrafluoroborates 316 can be stereoselectively prepared by... 

AUcynylstannanes can cross-couple with a variety of other functional groups employing the Stille protocol. Couphng to acyl chlorides is a well-known procedure that affords aUcynylketones in respectable yields. Other reports include alkynyltin cross-couplings with a-haloethers and a-halocarbonyls, enol phosphinates and phosphonates, alkenyl(phenyl)iodonium salts, alkynyl halides, and allyl hahdes (Table 9.18). Alkynylstannanes have also been shown to cross-couple with iron halides under the Stille conditions to effectively form iron-carbon bonds. 

In a recent series of studies focused on the synthetic utility of alkenyliodo-nium salts, ( )-/J-phenylethenyl(phenyl)- and ( )-l-hexenyl(phenyl)iodonium tetrafluoroborates, 22 and 23, were utilized for alkenylations of a range of soft, anionic nucleophiles (Scheme 45) [128-135]. In all cases but one, alkenylations with 22 occurred with retention of configuration, while alkenylations with 23 occurred with inversion of configuration. Only the dialkyl phosphoroselenolate salts gave mixtures of (Z)- and (fj)-products with 22 [132]. Furthermore, although cuprous iodide was used to catalyze the reactions of 22 and 23 with the phosphorothioate and -dithioate salts, the stereochemical results were the same [131,133]. It was generally assumed that retention was an outcome of the ligandcoupling or addition-elimination pathways, while stereochemical inversion was attributed to the vinylic... 

---