In contrast to the luminescent properties of its compounds, gold has only become of great interest in catalysis during the past decade.  The majority of that effort has focused on gold(I) complexes, their propensity for pi-coordination to alkynes and alkenes and their mildly electrophilic behavior.  As a follow-up to studies of electrocyclization reactions catalyzed by highly electrophilic Ir(III) cationic complexes, we commenced an examination of gold(III) chloride for catalysis in organic solvents of low polarity.  In this way, the addition of AuCl3 and AgSbF6 to these solvents was found to exhibit unprecedented activity for challenging transformations associated with Nazarov cyclization precursors. However, rather than a discrete cationic Au complex, a 1:2 mixture of AuCl3 and AgSbF6 generates a recyclable heterogeneous catalyst, the electrophilicity of which is comparable to the Ir(III) dicationic and tricationic catalysts previously found. In addition to the polarized Nazarov electrocyclization, the catalyst promotes an electrocyclization/lactonization sequence as well as 1,2 hydride shift/Friedel-Crafts alkylation sequences of 2-substituted furyl and benzofuryl enones. The true nature of the catalyst and its catalytic performance for various functionalized dienones will be discussed.

Recyclable heterogeneous gold catalysts for electrophilic chemistry of polarized dienones

244th National Meeting (2012)

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