4‐Dialkylaminopyridines as Highly Active Acylation Catalysts. [New synthetic method (25)]

TLDR

4‑dialkylaminopyridines, synthesized in two steps from pyridine, are roughly 10⁴ times more active acylation catalysts than pyridine and are increasingly employed for reactions that are incomplete or fail in pyridine, including group transfer in aqueous media. The article reviews the diverse applications of 4‑dialkylaminopyridines in terpene, steroid, carbohydrate, nucleoside chemistry, amino‑acid transformations to α‑acyl aminoketones, and isocyanate polymerization. Their exceptional catalytic activity, even in non‑polar solvents, arises from high concentrations of N‑acylpyridinium salts that exist as loosely‑bound, highly reactive ion pairs.

Abstract

Abstract The synthesis of 4‐dialkylaminopyridines can be accomplished in two steps starting from pyridine. Compared to pyridine, these derivatives are approximately 10 4 times more active when used as acylation catalysts. Dialkylaminopyridines are being used with ever‐increasing frequency for acylation reactions which proceed either incompletely or not at all in pyridine. This article reviews the various possible applications of 4‐dialkylaminopyridines in terpene, steroid, carbohydrate and nucleoside chemistry as well as in the transformation of amino acids into α‐acyl aminoketones and polymerization of isocyanates. In addition, N ‐substituted 4‐dialkylaminopyridinium salts can be used for the transfer of sensitive groups to nucleophiles in aqueous medium. The exceptional catalytic effect of these derivatives, even in non‐polar solvents, is due, in part, to the formation of high concentrations of N ‐acylpyridinium salts which are present in solution as loosely‐bound, highly reactive ion pairs.