Cyclizations copper trifluoromethanesulfonate

The reaction of crotonaldehyde and methyl vinyl ketone with thiophenol in the presence of anhydrous hydrogen chloride effects conjugate addition of thiophenol as well as acetal formation. The resulting j3-phenylthio thioacetals are converted to 1-phenylthio-and 2-phenylthio-1,3-butadiene, respectively, upon reaction with 2 equivalents of copper(I) trifluoromethanesulfonate (Table I). The copper(I)-induced heterolysis of carbon-sulfur bonds has also been used to effect pinacol-type rearrangements of bis(phenyl-thio)methyl carbinols. Thus the addition of bis(phenyl-thio)methyllithium to ketones and aldehydes followed by copper(I)-induced rearrangement results in a one-carbon ring expansion or chain-insertion transformation which gives a-phenylthio ketones. Monothioketals of 1,4-diketones are cyclized to 2,5-disubstituted furans by the action of copper(I) trifluoromethanesulfonate. ... 

Prof. Hao s synthesis commenced with the copper(I) chloride-catalyzed oxidation of the tryptamine derivative to afford ketone 42 [74], A three-component Strecker-type reaction was designed to react the ketone 42 with tryptamine and TMSCN to finish the first ring closure. After examining a series of both Lewis acid and Bronsted acids, the authors found a catalytic amount of TMSOTf promoted the transformation and afforded nitrile intermediate 43, which is ready for the Houben-Hoesch-type cyclization [75]. Treatment by TfOH (trifluoromethanesulfonic acid) [76] in DCM and the... 

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