Cycloaddition gold catalysis

The synthetic potential of gold catalysis, more especially for the generation of structural complexity, is particularly well illustrated by the total syntheses of Englerin A and B, reported independently in 2010 by Echavarren et al. and Ma et al. [31] (Scheme 16.26). A very similar approach was used by these two groups to produce, via a gold-catalyzed [2+ 2-1-2] intramolecular cycloaddition between an alkyne, an alkene, and a ketone, the core structure of the Englerins. Notably, this complex gold-catalyzed sequence, which operates with an absolute control of the stereoselectivity, allowed the creation of three new asymmetric centers and three new bonds (2 C-C and 1 C-O bonds). 

Very recently, as a consequence of their continuing interest in combining metal/ organic catalysis, Han et al. expanded the chemistry combining chiral phosphoric acid and gold catalysis. By incorporating an Au complex-catalyzed Danishefsky diene formation and chiral phosphoric acid-promoted enantioselective [4h-2] cycloaddition into the tandem reaction [69], they obtained pentacyclic frameworks in high yields and selectivities (Scheme 9.66). 

Harmata and Huang also accomplished a one-pot decomposition and intermolecular cycloaddition under gold catalysis to afford good yields of cycloadducts such as 102 and 103 directly (Scheme 18.22) [27]. The exact structure of the allyl cations or dienophiles in these reactions have not been delineated however, the gold-catalyzed reaction probably did not proceed via a retro-Diels-Alder reaction of 101 to generate sUoxyacrolein 87a in situ, because the cycloaddition of 87a required 24 h of reaction time under gold catalysis for... 

Because the palladium-catalyzed transannular [4+3] cycloaddition did not perform as well as desired, Gung et al. next explored the use of cationic gold catalysis as a... 

Togni A., Pastor S. D. Cooperativity of Chirality in Homogeneous Catalysis The Gold(I)-Catalyzed Aldol Reaction and the Vanadium(IV)-Catalyzed Hetero-Diels-Alder Cycloaddition Chirality 1991 3 331-340... 

Ngwerume, S., W. Lewis, and J.E. Camp. 2013. Development of a gold-multifaceted catalysis approach to the synthesis of highly substituted pyrroles Mechanistic insights via Huisgen cycloaddition studies. J Org Chem 78 920-934. 

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