Efforts Towards Control of Regioselectivity in the Gold(I) Catalyzed Hydration of Internal Alkynes. Effects of Solvent, Temperature and Substrate on Regioselectivity

Abstract

Internal alkyne hydration using gold(I) catalysts often shows < 5:1 regioselectivity. To explore factors that control selectivity, [(IPr)Au] + paired with the weakly coordinating anion [IMP-H] was employed in additive free hydration reactions. Solvent influences the anti-Markovnikov selectivity of alkylarylacetylene hydration. Although temperature does not impact selectivity, [(IPr)Au(NCMe)][IMP-H] (C1) is an effective precatalyst for alkyl/alkyl and alkyl/aryl acetylenes at ambient temperature. Overall kinetic behavior of C1 resembles that of other Au hydrofunctionalization reactions of [(IPr)Au] + , where nucleophilic attack and/or proton transfer are turnover limiting. Prospects for improving regioselectivity are discussed.

A catalytic system based on π–π stacking interactions between a pyrene substituted gold NHC catalyst and amphiphilic polymers for alkyne hydration reactions

“…As previously reported in the literature, counter anions play an important role in both the selectivity and performance of hydration reactions of internal alkynes. 16…”

Hydration of Unsymmetrical Internal Alkynes: Factors Governing the Regioselectivity

“…Recently, Dobereiner et al extensively studied various gold catalysts in the hydration reactions of a wide range of internal alkynes. , The authors observed, without trying to optimize the regioselectivity, that diarylalkyne 1g was regioselectively hydrated with a β-preference (β/α = 7.3/1) by using a zwitterionic N -heterocyclic carbene (NHC) gold catalyst (Scheme ).…”

Shape Selectivity in the Gold‐Catalyzed Hydration of Alkynes Using a Cavity‐Shaped Phosphine

“…Therefore the regioselectivity outcome can directly be affected by different factors such as substrate specificity, catalytic conditions ( ie . solvent) [6a,8] or the ligands employed [9] . In this work, we analyse and compare the selectivity (terminal vs internal alkynes) of the process derived from the well‐defined pocket of a cavity‐shaped gold complex with other gold catalysts presenting bulky phosphine ligands without a confined catalytic active site (Figure 1).…”