Structural Analyses of N‐Acetylated 4‐(Dimethylamino)pyridine (DMAP) Salts

Abstract

We have studied the formation of several N-acetyl-4-(dimethylamino)pyridine (DMAP) salts (with Cl(-), CH(3)COO(-), and CF(3)COO(-) counterions), which are considered to be the catalytically active species in DMAP-catalyzed acetylation reactions of alcohols. Combined crystal structure analyses, variable temperature matrix IR and NMR spectroscopy as well as computational techniques at the UAHF-PCM-B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) level were utilized to examine the structures and dynamics of salt formation. We found clear evidence for the formation of tight ion pairs that are stabilized by dynamic hydrogen-bonding interactions. In nonpolar solvents, the nucleophilicity of acetate in its N-acetyl-DMAP salt only allows a steady-state concentration smaller 1% at room temperature. Thus, we propose additional hydrogen-bonding interactions with alcohols to be the key stabilization factor in subsequent acetylations.

The aza-Morita–Baylis–Hillman reaction of electronically and sterically deactivated substrates

“…This is closely similar to interactions identified between acylpyridinium ions and carboxylate counter ions in pyridinecatalyzed acylation reactions. 22,23 In the adduct formed with PPh 3 (5a) the enolate oxygen atom is in direct contact with one of the phenyl ortho-C-H bonds.…”

6.08 Acylation-Type Reactions: Synthesis of Esters via Acyl Transfer

“…28 Additionally, the rate of the acylation is highly affected by the character of the anion and the solvent. 29,30 The first enantioselective approach of Vedejs et al required 1 equivalent of catalyst and two equivalents of a Lewis acid in the presence of base. The KR of aryl alkyl alcohols could be achieved with S≤45.…”

Applications of Nonenzymatic Catalysts to the Alteration of Natural Products

“…152 Thus, two additional products were achieved selectively through deliberate choice of the counterion (Figure 21C). When sterically hindered and electron-rich p - tert -butyl benzoic anhydride was screened, C4′–OH was selectively acylated ( 116 , Figure 21D).…”