Triazole–Au(I) complex as chemoselective catalyst in promoting propargyl ester rearrangements

Abstract

SummaryTriazole–Au (TA–Au) catalysts were employed in several transformations involving propargyl ester rearrangement. Good chemoselectivity was observed, which allowed the effective activation of the alkyne without affecting the reactivity of the allene ester intermediates. These results led to the investigation of the preparation of allene ester intermediates with TA–Au catalysts under anhydrous conditions. As expected, the desired 3,3-rearrangement products were obtained in excellent yields (generally >90% yields with 1% loading). Besides the typical ester migrating groups, carbonates and carbamates were also found to be suitable for this transformation, which provided a highly efficient, practical method for the preparation of substituted allenes.

Design and Synthesis of Alanine Triazole Ligands and Application in Promotion of Hydration, Allene Synthesis and Borrowing Hydrogen Reactions

“…Among the two typical oxidation states of gold catalyst, gold(I) complexes are considereda sh aving two coordination sites with linearg eometry, while those of gold(III) are accepted as having as quare planar geometry with four coordination sites, which should be conveniently fine-tuned by ligandc hanges (Scheme 1). [6] For gold(I), excellent examples are the development of PR 3 derivatives [7] and N-heterocyclic carbene( NHC) ligands, [8] which greatly enhancedt he catalyst stability and enriched the catalytic applications of gold catalysts through metal-ligand back-bonding. Meanwhile, gold(III) complexes have usually been stabilized by bidentatea nd tridentate ligands.…”

Insights into the Gold‐Catalyzed Propargyl Ester Rearrangement/Tandem Cyclization Sequence: Radical versus Gold Catalysis—Myers–Saito‐ versus Schmittel‐Type Cyclization

“…In the case of allenyl acetate 6x under gold catalysis we detected the formation of the 6-endo cyclization/elimination product 5x (Scheme 5b). As the thermal/radical reactions give rise to different cyclization products,t hese experiments clearly demonstrate ad omino gold-catalyzed reaction and not ad omino gold/radicalcyclization with an allenyl acetate inter- [20] Unfortunately,t his reactionw as unselective and based on in situ NMR spectra we could identify small amountso fatwofold gold-catalyzed domino transformation as well as the gold/radicalc yclization product.…”

“…As the thermal/radical reactions give rise to different cyclization products, these experiments clearly demonstrate a domino gold‐catalyzed reaction and not a domino gold/radical cyclization with an allenyl acetate intermediate being involved. However, we were interested in using triazole catalyst [Ph 3 PAu(triazole)OTf], which is known for generating the allene intermediate from propargylic esters without catalyzing following cyclization reactions 20. Unfortunately, this reaction was unselective and based on in situ NMR spectra we could identify small amounts of a twofold gold‐catalyzed domino transformation as well as the gold/radical cyclization product.…”

Dehydrierende Meyer‐Schuster‐Umlagerung: Gold‐katalysierte Synthese von Alkinen

“…Mithilfe des Acetats, das bei der Bildung der Zwischenstufe C freigesetzt wird, wird das b-H eliminiert, was zur Bildung des Endprodukts 2 führt. Darüber hinaus versuchten wir, die Allen-Zwischenstufe mit dem neuen und effizienten Katalysator Triazol-Au (TA-Au), der von Shi et al [15] entwickelt wurde, zu isolieren. Erfreulicherweise konnte die Allen-Zwischenstufe in 85 % Ausbeute isoliert werden.…”