Transition‐Metal‐Catalyzed Direct Substitution of Alcohols in Aqueous Media

Abstract

The direct use of alcohols as the much greener and more sustainable alkylated reagents in substitution reactions is one of the emerging areas in green chemisty. However, owing to the poor leaving character of OH group, the direct substitution of alcohols is not an easy thing. Transition metal (TM) catalysis such as Pd‐catalyzed allylic/benzyl substitution and Ir‐catalyzed borrowing hydrogen provides efficient protocols for the direct substitution of alcohols, however, an organic solvent and servely anhydrous conditions are generally required. In recent decade, TM‐catalyzed direct substitution of alcohols in aqueous media was developed as a much greener alternative. In this review, the recent develpoments of this area are summarized. The activation mechanism of alcohols in aqueous reactions are emphatically discussed.

Naturally occurring phytic acid: an advanced Brønsted acid catalyst for direct amination reactions of allylic alcohols

“…8 Hence, this transformation using free alcohol, forming water as the sole by-product, is a more sustainable process, but the catalyst must be water resistant and able to activate an unreactive hydroxyl group. Palladium 9 and other transition metals 10 have been intensively employed as catalysts in this regard, and they mostly proceed through a π-allylic intermediate, while Lewis acid catalysts have been less studied 11 (Scheme 1b). There are even fewer examples of Brønsted acid catalysts, which typically go through an allylic carbocation intermediate via an S N 1 mechanism.…”

The Visual Preparation of n-Bromobutane

“…With our continuous interest in substitution of alcohols, this paper proposes a visual preparation of n -bromobutane in a typical ∼3 h laboratory class. A Dean–Stark apparatus, a common glass apparatus in the basic organic chemistry laboratory, was used so that it is simple and convenient for students to visually monitor the reaction process; i.e., students can observe that n -bromobutane keeps moving from the upper layer through the water layer to the lower layer in the Dean–Stark apparatus.…”

Pd-Catalyzed Aerobic Synthesis of Allylic Sulfones from Allylic Alcohols and Sulfonyl Hydrazines in Water

“…Besides, they are also key intermediates which are widely used in organic synthesis . Therefore, numerous methods including the oxidation of thioethers, hydrosulfination of unsaturated compounds, and TM-catalyzed cross-couplings were developed for the synthesis of allylic sulfones. Among them, the Tsuji–Trost reaction is very attractive due to its high chemo- and regioselectivity .…”