Mercuric triflate revisited: Development of catalytic reactions

Hg(OTf)(2), developed in our group in 1983 as an olefin cyclization agent, has been developed further into a powerful catalyst for the hydration of terminal alkynes leading to methyl ketones. The reaction is speculated to involve Hg2+-induced hydration of alkyne followed by protodemercuration caused by the in situ generated TfOH that also results in the regeneration of Hg(OTF)(2). In the presence of an appropriately placed double bond or an aromatic ring, enyne as well as arylyne cyclizations take place with 1000 catalytic turnover. The cyclization of yne-en-aryl substrates leading to tricarbocycles is the first Hg2+-catalysed biomimetic tandem cyclization. Hg(OTf)(2) is useful not only for carbon-carbon bond formation but also for the synthesis of heterocycles such as furans, indoles, and exomethylene enol lactones. A novel Hg(OTf)(2)-catalyzed glycosylation using alkynoate as leaving group has also been developed. This protocol is useful for the preparation of hindered glycosides. Hg(OTf)(2)-catalyzed reaction of an internal propargyl acetate with water constitutes a novel procedure for enone synthesis.