AuCl₃‐Catalyzed Hydroalkoxylation of Conjugated Alkynoates: Synthesis of Five‐ and Six‐Membered Cyclic Acetals

Abstract

The AuCl3‐catalyzed double hydroalkoxylation of conjugated 7‐hydroxyheptynoates offers a convenient route for the synthesis of six‐membered cyclic acetals, which are common substructures of polyketide natural products. When conjugated 6‐hydroxyhexynoates are used as starting materials, either five‐membered cyclic E‐enol ethers or the corresponding acetals can be obtained by simply choosing the appropriate reaction solvent. NMR spectroscopic studies were carried out to determine the kinetics and pathway of the latterdomino 5‐exo cyclization–hydroalkoxylation reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Lanthanide‐Catalyst‐Mediated Tandem Double Intramolecular Hydroalkoxylation/Cyclization of Dialkynyl Dialcohols: Scope and Mechanism

“…Most of these transformations produce cyclic or bicyclic acetals using transition‐metal catalysts via intermolecular or intramolecular pathways. Tandem intermolecular hydroalkoxylation processes include the formation of cyclic acetals from alkynyl alcohols and another alcohol such as MeOH or EtOH using AuCl 3 ,11 [AuCl(Ph 3 P)],12 or [{Ir(cod)Cl} 2 ] catalysts [e.g., Eqs. (1) and (2)] 13.…”

Platinum‐Catalyzed Regioselective Formation of β‐Alkoxy Ketones from Internal Alkynes

“…With compound 1 as the test sub-strate, the catalytic activity and regioselectivity of different transition metals were evaluated with a catalyst loading of 5 mol-%. In sharp contrast to the gold-catalyzed hydroalkoxylation of conjugated alkynoates reported recently, [10] simple gold catalysts, such as gold(I) chloride, gold(III) chloride, and sodium tetrachloroaurate(III) dihydrate, do not show any activity even at 60°C, and Au(PPh 3 )Cl/AgOTf afforded 3a as the only detectable product (Table 1, Entries 1-4). [11] Mercury triflate displayed the same unfavorable regioselectivity, preferring an 8-endo-dig product (Table 1, Entry 5).…”

Transition Metal‐Catalyzed Hydroalkoxylation of Alkynes: An Overview

“…Gold-catalyzed tandem intramolecular hydroalkoxylation-intermolecular oxa-Michael addition of various internal alkynols 80, with alcohols for the synthesis of tetrahydropyran derivatives 81 was reported by Ley and co-workers (Scheme 32). [39] The reaction proceeded smoothly on the expected lines to deliver various THP-derivatives in excellent yield, more importantly, in all the cases only one diastereomer was obtained. The reaction mechanism involved 6-exo-dig hydroalkoxylation to generate exocyclic enol ether Int-H, which upon intermolecular oxa-Michael addition afforded corresponding cyclic ethers.…”