Catalyzed Catalysis Using Carbophilic Lewis Acidic Gold and Lewis Basic Palladium: Synthesis of Substituted Butenolides and Isocoumarins

Abstract

A new strategy for gold and palladium dual-catalytic reactivity and turnover, called catalyzed catalysis, enhanced the synthetic usefulness of vinylgold intermediates by providing dual-catalytic carbon-carbon cross-coupling as an alternative to protodemetalation. This protocol enabled the synthesis of substituted butenolides and isocoumarins from allyl esters. Kinetic and spectroscopic experiments support a mechanism in which the Lewis acidic gold complex catalyzes both an initial rearrangement step and a subsequent Lewis basic palladium oxidative-addition step.

On Homogeneous Gold/Palladium Catalytic Systems

“…This could easily be assigned by the comparison with the known spectroscopic data of the related compounds of Asao [17b] or Blum. [9] The propargylic ester 18a did not deliver product 19a under the different conditions applied (entries 1, 2, 5 and 6; column 18a). Different amounts of the cyclisation product 17a were obtained.…”

“…The test substrate 6a is identical to the one which was also used by Blum et al [9] The first experiment was the use of Asaos conditions (7.5 mol% Ph 3 PAuCl, 7.5 mol% AgOTf, benzene, room temperature), [17b] product 17a was obtained selectively, but only 30% yield and 50% conversion were reached (Scheme 7). There was no evidence in the GC-MS of the crude material for the allylation product 7a.…”

“…Now Blum et al have reported a reaction specific to allylic esters 4 as substrates, which is catalytic in both gold and palladium (Scheme 2). [9] The reaction is a special case, as the intermediate C is related to Hammonds [10] vinylgold intermediates and thus, unlike other vinylgold intermediates, is stable (not sensitive to protodeauration like most other vinylgold species from catalytic cycles). So there is no competing reaction and C is waiting for the palladium catalyst to form the product 5 via intermediate D. These reactions in a very clever way exploit the activity of allylic oxonium intermediates as allyl-transfer reagents and at the same time avoid the presence of protons usually going along with gold-catalysed nucleophilic additions.…”

“…In their publication, Blum et al [9] also reported a second related reaction, involving allylic o-alkynylbenzoates 6 (Scheme 3). As above, an activated allylic species E is formed (equivalent to species C), but in this case the vinylgold intermediate F would be more sensitive than the species D discussed above.…”

Heterocyclic chemistry

“…When performed in the presence of asymmetric gold catalysts, moderate enantioselectivities were observed (50 -71% ee). Furanones have attracted attention, 35,36,37 and several approaches to these important synthetic building blocks are shown in Scheme 22. Thus, Kumar and co-workers This journal is © The Royal Society of Chemistry [year] have A simple one-pot route to N-arylpyrazoles from di-tert-butylazodicarboxylate (DBAD), aryl nucleophiles (derived from aryl halides in the presence of n-BuLi) and 1,3-dicarbonyls has been reported (Scheme 25).…”