Water Compatible Gold(III)‐Catalysed Synthesis of Unsymmetrical Ethers from Alcohols

Abstract

An efficient and broad-scoped method for the preparation of unsymmetrical ethers from alcohols catalysed by the simplest and least expensive gold catalyst, NaAuCl(4), is described for the first time. The procedure enables the etherification of benzylic and tertiary alcohols with moderate to good yields under mild conditions with low catalyst loading. Symmetrical ethers, the usual side products in the etherification of alcohols, were not detected in this case. The formation of the racemic ether from a chiral benzyl alcohol suggests the intermediacy of a carbocation, which has not previously been postulated for gold-catalysed reactions involving alcohols.

Direct Nucleophilic SN1‐Type Reactions of Alcohols

“…S N 1-Type reactions in the presence of a palladium catalyst was described in 2003 by AbuOmar. [122] He reported one of the first articles in this field involving the direct use of cationic palladium complexes [(R,R)-DiopPd(OTf) 2 (112) obtained in situ by exchange with AgOTf]. Although chiral ligands were employed in the reaction that occurred in nitromethane at 50°C, mixtures of diastereomers and no enantiomeric excess values were obtained consistently (Scheme 35).…”

“…The use of NaAuCl 4 in the preparation of ethers was reported by Asensio [112] in an efficient and broad-scoped method for the preparation of unsymmetrical ethers from alcohols. The procedure enables the etherification of benzylic alcohols 1 and 2 and tertiary alcohol 9 with moderate to good yields under mild conditions with low catalyst loading, leading to the formation of unsymmetrical ethers.…”

A new versatile binuclear seven-coordinate complex of molybdenum(II), [(μ-Cl)2{Mo(μ-Cl)(SnCl3)(CO)3}2]2−

“…Although the dehydration of alcohols to ethers has been recently observed in the presence of transition metal catalysts [35][36][37][38][39][40][41][42] the formation of ether in one-pot synthesis from olefin is very scarce [43][44]. The reaction catalyzed by 1 not only proceeds under very mild conditions but is selective as well.…”

Thiazolium‐Based Catalysts for the Etherification of Benzylic Alcohols under Solvent‐Free Conditions

“…Very recently, Roth et al reported a direct reductive synthesis of several ethers through a combination of organosilanes and triflic acid. [31] In most of cases, the methods based on transition metal catalysts display good performances, however, the homogeneous conditions used and the elevated price of the metals limit their large-scale applications. [15] Alternative routes have been investigated, for example, the use of UV irradiation, [16] dimethyl sulfoxide, [17] and phase-transfer catalysts.…”