Chemoselective and stereospecific iodination of alkynes using sulfonium iodate(i) salt
Dodla S Rao1, Thurpu R Reddy, Sudhir Kashyap
1Department of Chemistry, Malaviya National Institute of Technology (MNIT), Jaipur-302 017, India. skashyap,chy@mnit.ac.in skr.kashyap@gmail.com.
Abstract:
An efficient and highly chemoselective iodination of alkynes using a sulfonium iodate(i) electrophilc reagent under metal-free conditions has been realized. The reactivity of sulfonium iodate(i) salt could be significantly diverse in the presence of water as the solvent, enabling the (E)-1,2-diiodoalkenes stereospecifically. This stereodivergent approach is amenable to a wide range of alkyne substrates and demonstrates a diverse functional group tolerance resulting in synthetically valuable 1-iodoalkyne and (E)-vicinal-diiodoalkenes in good to excellent yields (up to 99%) with 100% selectivity under ambient conditions.
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Acidity of 1-Alkynes
The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.


