Iridium-catalyzed addition of methanol to terminal alkynes

The 18-crown-6 (18C6) ether adduct of sodium hexachloroiridate [Na(18C6)]2[IrCl6]·xH2O (1) was found to catalyze an addition of methanol to a variety of nonfunctionalized alkynes RCCH (R = H, nPr, nBu, nPen, Ph, HCC(CH2)4) yielding the corresponding Markovnikov addition products (ketals) and in the cases of hex-1-yne and hept-1-yne also anti-Markovnikov ones (acetals, <10%). Furthermore, the reaction of methanol with octa-1,7-diyne resulted in a double Markovnikov addition to only one triple bond, yielding 7,7-dimethoxyoct-1-yne with 80% degree of conversion. On the other hand, the regioselectivity in an addition of methanol to functionalized terminal alkynes of the type RC(O)CCH (R = OMe, Me) was found to be towards anti-Markovnikov products (70–93%). In these two cases vinyl ether intermediates were observed NMR spectroscopically in the course of the reactions.

The 18-crown-6 (18C6) ether adduct of sodium hexachloroiridate [Na(18C6)]2[IrCl6]·xH2O (1) was found to catalyze an addition of methanol to a variety of nonfunctionalized alkynes RCCH (R = H, nPr, nBu, nPen, Ph, HCC(CH2)4) yielding mainly the Markovnikov addition products (ketals) (>90%). In contrast, the regioselectivity in an addition to functionalized terminal alkynes RC(O)CCH (R = OMe, Me) was found to be towards anti-Markovnikov products (70–93%). Figure optionsDownload as PowerPoint slide