Alkynyliodonium tetrafluoroborates reactions

Despite the synthetic possibilities suggested by this early study, the chemistry of the alkynyliodonium salts lay dormant until the mid-1980s. In 1986, Ochiai and his coworkers published an important communication which shaped much of the later thinking on the reactions of alkynyliodonium ions with nucleophiles28. When / -dicarbonyl enolates are treated with alkynyliodonium tetrafluoroborates containing a long (> three carbons) alkyl chain, derivatives of cyclopentene are produced. This is illustrated in equation 41 for the... 

The seminal paper which led to the revival of alkynyliodonium chemistry was published by Ochiai et al in 1986. The reaction of p-diketone enolates with alkynyliodonium tetrafluoroborates containing an alkyl chain led to the formation of cyclopentene derivatives such as (81). 1 ... 

The onium transfer reaction between alkynylphenyliodonium tetrafluoroborates and triphenylarsine afforded high yields of 1-alkynyltriphenylarsonium tetrafluoroborates.However, this reaction appeared to be mechanistically at variance with the generally admitted patterns of reactivity of alkynyliodonium salts. Reaction of phenyl(phenylethynyl-2- C)iodonium tetrafluoroborate (88) (99% enriched) led to the arsonium salts (89) with more than 95% of enrichment on the p>carbon atom. Although the Michael carbene pathway was not totally excluded, the ligand coupling pathway seemed therefore more important. 

Reaction of P-functionalized alkynyliodonium triflates, 11, with LiNPh2 results in various push-pull ynamines, 67, in 43-66% isolated yields [56] [Eq. (27)]. Treatment of alkynyliodonium tetrafluoroborates with Me3SiN3 in wet CH2CI2 results in the stereoselective formation of (Zy-P-azidovinyl iodonium salts 68 [Eq. (28)] in 50-91 % isolated yields [57]. 

The alkynylation of phosphorus nucleophiles has been less investigated (Scheme 7). Ochiai and co-workers first demonstrated in 1987 that the alkynylation of triphenyl-phosphine was possible with alkynyliodonium tetrafluoroborate salts under light irradiation (Scheme 7, A) [69]. The reaction most probably involves radical intermediates. In 1992, Stang and Critell showed that light irradiation was not needed if alkynyliodonium triflates were used [70]. Later, this methodology could be extended to other triaryl- or alkyl phosphines [71, 72]. In 1990, Koser and Lodaya also reported the synthesis of alkynylphosphonates by the Arbusov reaction of alkynyliodonium tosylates with trialkyl phosphites (Scheme 7, B) [73]. Alternatively, the same compotmds can be obtained by the reaction of alkynyliodonium tosylates with sodium phosphonate salts [74]. 

The alkyl chain in such MCI reactions need not be restricted to the alkynyliodonium component. For example, the treatment of sodium 2-n-hexyl- 1,3-indandionate with 1-propynyl(phenyl)iodonium tetrafluoroborate in THF affords the spiro-nonene system shown in equation 4228. 

When / -dicarbonyl enolates are allowed to react with alkynyliodonium salts, typically in ter/-butyl alcohol or THF, alkynyl- and/or cyclopentenyl- -dicarbonyl compounds are obtained. The product compositions are largely regulated by the migratory aptitude of R in the alkynyl moiety and the availability of alkyl side chains for the MC-insertion (MCI) pathway (equation 45). These divergent modes of reactivity are nicely illustrated by the reactions of the 2-phenyl-1,3-indandionate ion with ethynylfphenyl)- and 4-methyl-1-hexynyl(phenyl)iodonium tetrafluoroborates (equation 1 15)27 2. 

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