Abstract
With the increasing concern for sustainability, the use of environmentally friendly media to perform chemical processes has attracted the attention of many research groups. Among them, the use of water, as the unique solvent for reactions, is currently an active area of research. One process of particular interest is the direct nucleophilic substitution of an alcohol avoiding its preliminary transformation into a good leaving group, since one of the by-products in this approach would be water. The direct substitution of allylic, benzylic, and tertiary alcohols has been achieved through SN1-type reactions with catalytic amounts of Brønsted or Lewis acids; however, organic solvents are often required. In this review, the pioneering SN1 approaches performed in pure water and in the absence of a metal based Lewis acid are compiled and discussed.
Highlights
The direct nucleophilic substitution of an alcohol through an SN 1-type reaction has been attracting chemists’ attention for many years [1], since one of the by-products in this process is water, and, due to the interest in trapping the resulting carbocation intermediate
The direct generation of carbocations on water from alcohols is probably driven by the formation of hydrogen bonds between water and the hydroxy group of the alcohol
Reaction has been a challenge for many research groups for many years. The interest in this reaction has increased due to the fact that water is the only by-product in this process and because the resulting carbocation intermediates can be trapped
Summary
The direct nucleophilic substitution of an alcohol through an SN 1-type reaction has been attracting chemists’ attention for many years [1], since one of the by-products in this process is water, and, due to the interest in trapping the resulting carbocation intermediate. For the activation of these SN 1-type reactions using allylic, benzylic, and tertiary alcohols, a catalytic amount of a metal based Lewis acid is normally used [2,3,4,5,6]. In the continuous search for a more environmentally friendly medium, the use of water as solvent or as co-solvent for reactions has received considerable attention in recent years [19]. High temperature or the use of a co-catalyst or an acid additive is necessary
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