Cycloaddition gold-catalyzed

In 2008, a gold-catalyzed cycloaddition of captodative dienynes with nitriles to provide pyridines was developed [114], The reaction proceeded via intermolecular hetero-dehydro-diels-alder cycloaddition and gave the desired pyridines in good yields regioselectively (Scheme 3.56). 

The entfo-cyclization takes place as a minor pathway in certain cases, but is the favored one in platinum- and gold-catalyzed cycloaddition of related arylenynes with enesulfonamides or enamines [221-223]. Analogous tricylic products can be synthesized via gold-catalyzed [4+2] cycloaddition reaction of benzyl-substituted... 

A selectivity divergence between phosphite and NHC ligands was also reported in the gold-catalyzed cycloaddition of allenedienes [eqn (4.8)]. With the IPr ligand on the putative active species LAu, which is generated in situ by anion metathesis using a silver salt, the major product obtained from substrate 123 is the formal [4C+3C] cycloaddition product 124. On the... 

Other gold-catalyzed cycloaddition reactions have been reviewed [143]. 

Gold-catalyzed intramolecular [4+2] cycloaddition of furans with alkynyl substituents led to the formation of phenol derivatives, A mechanistic study showed that a transposition of the oxygen from the carbon atoms of furan to the former terminal carbon of the alkynes seemed to occur through an intramolecular mode and the epoxide depicted below was presumably an intermediate <01OL3769>. 

Representative procedure for the gold-catalyzed [2+2]-cycloaddition of alkenes with alkynes. l,3-Diphenyl-3-methylcyclobuten ... 

Representative procedure for the gold-catalyzed intramolecular [4+2]-cycloaddition of 1,6-enynes. Dimethyl 3,3a-dihydroacephenanthrylene-4,4(lH,5H,10bH)-dicarboxylate ... 

Scheme 4.14 Gold catalyzed synthesis of azepines via an intermolecular Diels-Alder cycloaddition.

The gold-catalyzed formal cycloaddition reactions of 2-ethynylbenzyl ethers with 8-methylquinoline oxide and ethyl diazoacetate led to a skeletal rearrangement of the benzo[c]furan motif through an attack of the diazo compound on the initial oxonium species in the alkyne activation route, followed by a Roskamp-type rearrangement and ring closure (13AGE7559). 

Oxabicyclo[3.2.1]oct-3-ene derivatives can be prepared by a gold(I)-catalyzed cycloaddition reaction of alkynes with oxoalkenes (Scheme 9) (13CEJ3547). In a similar procedure, a gold(III) catalyst mediates an efficient oxidative domino cychzation—cycloaddition reaction of enyne aldehydes and ketones to give polyfimctionalized tetracyclic ketoethers (Scheme 10) (13CEJ14787). 

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). 

In a separate communication, Helmchen and coworkers showed that di-f-butylsilyl-protected 1,3-diol-enyne 39 underwent a di-astereoselective gold(I)-catalyzed cycloaddition of o-nitobenz-aldehyde yielding 2-oxabicyclo-[3.1.0]hexane 40 in 58% yield (eq 17). ... 

In addition, the gold-catalyzed intermolecular reaction of alkynes with alkenes leads to cyclobutene compounds (Scheme 1.27) [201]. This transformation shows that in the absence of constrains imposed by the tethers in the intramolecular processes, a [2-I-2] cycloaddition is the predominant mechanism. 

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