Recent Advances in the Gold-Catalyzed Reactions of Propargyl Esters

Abstract

Conspectus Late-transition-metal-based complexes represent an indispensable catalytic tool in chemical synthesis due to their ability to increase molecular complexity rapidly and efficiently from readily accessible substrates in a single operation. Added to this is the exquisite control of product chemo-, diastereo-, enantio-, and site-selectivities achieved by catalytic systems of the transition-metal salts that have been developed to mediate a wide range of functional group transformations. Within this venerable synthetic toolbox, complexes and salts of Au­(I) and Au­(III) have emerged in recent years as an invaluable addition as a result of their potent σ- and π-Lewis acidities and ability to stabilize cationic reaction intermediates. The insights provided by mechanistic studies examining the various electronic, steric, and stereoelectronic factors at play in the organogold species that are expected to be formed in the catalytic chemistry of the transition-metal complex have also been pivotal in understanding and exploring their potential synthetic utility. Illustrative of this, for example, is the contribution made by the gold-catalyzed cycloisomerization chemistry of propargyl esters in synthetic strategies to a variety of bioactive natural products and compounds of current pharmaceutical and materials interest. This Account summarizes our efforts over the past decade toward realizing new single-step strategies for carbocyclic and heterocyclic synthesis that relied on the gold-catalyzed reactions of propargyl esters. It outlines synthetic methods developed by the group that exploited the unique reactivities of the gold-carbene species typically generated from the [2,3]-sigmatropic rearrangement of the compound class containing a terminal or electron-deficient alkyne moiety on exposure to the transition-metal salt. This Account also describes the realization of synthetic methods initiated by the gold-catalyzed 1,3-acyloxy migration of propargyl esters with an electronically unbiased disubstituted CC bond that delivers the corresponding allenyl ester that is primed for further reactivity on activation by the group 11 metal complex. The studies formed a part of an ongoing overarching program within our group that was focused on determining reactivities in gold catalysis that would enable their application as readily recognizable disconnections in retrosynthetic analysis. They were additionally a part of efforts aimed at evaluating the opportunities offered by the relativistic effects possessed by a Au­(I) and Au­(III) complex, the most pronounced among the d-block elements and thus the catalyst of choice in alkyne activation chemistry, to generate new chemical space. For instance, we demonstrated in several studies the cycloisomerization of 1,3- and 1,4-enyne esters to be a reliable strategy for the in situ formation of a wide range of 1,4-cyclopentadienyl derivatives. Their further reaction with an appropriately placed functional group or a second starting material was then shown to afford a variety of synthe...

Gold-catalyzed cyclization and cycloaddition in natural product synthesis

“…[89][90][91] The diversity of products accessible through gold-catalyzed transformations of propargylic esters has expanded signicantly over the past two decades. [92][93][94] Isolated from the roots of Ormosia hosiei Hemsl & E. H. Wilson, hosieine A (111), a novel class of cytisinelike lupin alkaloids, has demonstrated potent activity against the nicotinic acetylcholine receptor a 4 b 2 , with a IC 50 value of 0.96 nM. 95 The compelling bioactivity and the limited natural abundance of hosieine A have spurred Wood and co-workers to develop a streamlined synthesis route for this alkaloid in both racemic and enantioenriched forms (Scheme 16).…”

Gold catalyzed spirocyclization of 1-ene-4,9- and 3-ene-1,7-diyne esters to azaspiro[4.4]nonenones and azaspiro[4.5]decadienones

“…Gold-catalyzed cycloisomerization of 1, n -enynes and their ester analogues has emerged over the years as one of the most powerful and versatile synthetic methods to rapidly and efficiently increase molecular complexity in a single operation. 10–19 An illustrative example of this is the synthesis of cyclopentenones that relies on the gold( i )-catalyzed cascade [3,3]-sigmatropic rearrangement/Nazarov cyclization of 1,3-enyne acetates and the hydrolysis of the ensuing 1,3-cyclopentadienyl ester intermediate (Scheme 1a). 11 The synthetic utility of the in situ formed 1,3-cyclopentadienyl ester species was next demonstrated by studies that showed the highly reactive intermediate could be engaged in gold-catalyzed cascade intermolecular electrophilic halogenations, allylic alkylations, Schmidt-type reactions with aryldiazonium salts, and Diels–Alder reactions.…”

Insights into the mechanism and origin of solvent-controlled chemodivergence in the synthesis of Au-catalyzed bicyclo[2.2.1]heptanes from 3-alkoxy-1,6-diynes: a DFT perspective

“…Notably, the protodeauration process represents a novel approach in the synthesis of bridged ring systems, distinct from the previously reported protodeauration of alkyl-gold intermediates. 8 This new reactivity concept holds promise for uncovering unconventional methods to synthesize bridged ring systems.…”