Alkynyliodonium tetrafluoroborates with enolates

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 ... 

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. 

The treatment of the thermodynamic enolate of 2-methylcyclohexanone with ethynyl(phenyl)iodonium tetrafluoroborate in tetrahydrofuran affords 2-ethynyl-2-methylcyclohexanone (equation 267). This is the only example known to this author of the alkynylation of an unactivated monocarbonyl compound with an alkynyliodonium salt. However, the earlier conclusion that simple enolates do not undergo alkynylation with alkynyliodonium salts (section II.D.7 and II.G) needs to be revvised. 

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