Ionic core dependence of ionophilic thiourea organocatalysis in ionic liquids

Abstract

The Morita-Baylis-Hillman reaction forms a carbon-carbon bond between an electrondeficient alkene and an aldehyde in an atom economic, albeit slow, reaction in the presence of catalytic tertiary amine or phosphine.1 Utilizing a methylpiperidinium derived ionic thiourea co-catalyst, 6, in the Morita-Baylis-Hillman reaction between benzaldehyde and 2-cyclohexene-1-one with DABCO resulted in a rate acceleration and appreciable conversion to the product, 2-(hydroxyl(phenyl)methyl)cyclohex-2-enone, 1, within two days. Additionally, recycling of the methylpiperidinium thiourea organocatalyst, 6, was attempted in order to facilitate reuse of the catalyst by entrainment in two ionic liquids, [BMPyr][N(Tf)₂] and [BMPP][N(Tf)₂]. The percent conversions to the product of the first two trials were 89% and 88%, but on recycling, this decreased to 54% and 66% conversion respectively. The methylpiperidinium thiourea organocatalyst, 6, was not able to be successfully recycled and did not maintain catalytic activity.