Tetraarylphosphonium-Supported Carbodiimide Reagents:  Synthesis, Structure Optimization and Applications

Abstract

New tetraarylphosphonium (TAP)-supported alkyl- and arylcarbodiimides were synthesized and used as coupling reagents for esterification reactions, amidation reactions and dehydration reactions of hydroxyesters. Taking advantage of the solubility properties imparted by the tetraarylphosphonium unit, a simple precipitation and filtration allowed complete separation of the urea by-products. This paper describes the structure optimization study of the various TAP-supported carbodiimide reagents to obtain the desired reactivity and solubility profile. Furthermore, we have demonstrated that the diimide reagent can be regenerated from the urea to recycle the reagents.

Amide bond formation: beyond the myth of coupling reagents

“…161 Charette ''attached'' carbodiimides to tetraarylphosphonium salts as a means of ''tagging'' the reagent. 162 Reaction was carried out in solution phase, before precipitation of the salt with apolar solvents. Several carbodiimides derivatives 192 were synthesised (Fig.…”

Nickel‐Catalyzed Synthesis of Phosphonium Salts from Aryl Halides and Triphenylphosphine

“…[10,11] Recently, we reported that the tetraarylphosphonium (TAP) unit can be used as a solubility control group to modify and predict the solubility properties of supported reagents and synthetic intermediates. A number of TAP-supported reagents derived from triphenylphosphine, diethyl azodicarboxylate, [12] tributyltin chloride, [13] and dialkylcarbodiimide [14] have been prepared and successfully used in various reactions. Furthermore, the reagents by-products can be removed from the reaction medium by a precipitation/ filtration sequence.…”

Lesser-Known Enabling Technologies for Organic Synthesis

“…For instance, the tetraarylphosphonium-tagged carbodiimides 201 have been used recently in a series of reactions including esterifications (Scheme 36), amidations and dehydrations. 79 The reactions were carried out in dichloromethane, in which the tetraarylphosphonium species were highly soluble, and after reaction was complete the addition of diethyl ether caused their complete precipitation. The products 205 were then recovered in high yield and high purity simply by filtration.…”