(N-benzylmethylaminopyridine polymer bound; N-methyl-N-(4-pyridyl)aminomethyl-polystyrene cross-linked with divinylbenzene; reagent used as recyclable catalyst for acylation reactions)
Form Supplied in: 2-4% cross-linked poly(styrene-co-divinylbenzene) as resin type; commercially available.
Analysis of Reagent Purity: typical loading 2.5-3.0 mmol N g-1 (dry).
Preparative Methods: several syntheses for typical polymeric forms of (dimethylamino)pyridine have been published: (i) Condensation reaction of laurylated poly(ethyleneimine) with 3-[N-methyl-N-(4-pyridyl)amino]propionic acid.1 (ii) Substitution reaction of polystyrene bearing (methylamino)methyl substituents with 4-chloropyridine.2 (iii) Copolymerization of 4-(N-methyl-N-para-vinylbenzylamino)pyridine, styrene and commercially available divinylbenzene (DVB).3 (iv) Chemical modification of halogenated bead polymers such as chloromethylstyrene copolymer with 4-(N-methylamino)pyridine.4
Polystyrene-bound dimethylaminopyridine (PS-DMAP) is a polymer-bound equivalent of 4-(dimethylamino) pyridine (DMAP)5 which may be used as a catalyst for acylation and related reactions. PS-DMAP can be recovered easily from the reaction mixture and is recyclable. Therefore, PS-DMAP can be used in flow systems such as packed or fluidized bed reactors.
The application of PS-DMAP as a catalyst for the acylation of hydroxy groups with acid anhydride has been investigated, in particular for acetic anhydride. Catalytic PS-DMAP accelerates the acylation of sluggish nucleophiles, e.g. tertiary alcohols. The catalytic activity of PS-DMAP for the acylation of linalool (
Although the acetylation is hardly catalyzed by triethylamine alone, it proceeds easily in the presence of PS-DMAP.3 The activity of PS-DMAP, cross-linked with 2 mol % divinylbenzene (DVB), is slightly lower than that of DMAP. In this reaction, the catalyst is recovered by filtration, washed with aqueous sodium hydroxide and acetone, and the recovered PS-DMAP can be reused without a significant reduction in catalytic activity.
The reaction mechanism suggests that the catalytic activity of DMAP moiety is due to both the increased electron-donating ability of the ring nitrogen and the increased stability of the acetylpyridinium species.1a,3,6
PS-DMAP can also be used for O-acetylation of enols (
PS-DMAP beads act as a catalyst for ester syntheses by the dicyclohexylcarbodiimide (DCC) method (
In the esterification of benzoic acid with MeOH by the DCC method, the process catalyzed by the polymer-bound reagent is relatively slow and the yield is lower than with DMAP under homogeneous conditions (
In the esterification of N-protected amino acids using dimethyl dicarbonate (
PS-DMAP may also be used as a stoichiometric polymer-bound acylium repository for N-substituted acyl pyridinium salts derived from acid chlorides, and a variety of acyl derivatives, including esters, amides, and thioesters can be synthesized in this way. The electrophilic component is reacted with PS-DMAP and an acyl pyridinium salt forms which is then reacted with various nucleophiles such as alcohols, amines, and thiols without addition of a tertiary amines base (
The key to this approach is the ability to purify the polymer-bound acylium salt by solvent washes. When the nucleophile is used as the limiting reagent, the product is isolated in high purity by filtration, with the excess electrophile remaining bound to the resin.
PS-DMAP and isobutyl chloroformate act as a polymeric activating agent for carboxylic acids to form the mixed carbonic-carboxylic anhydride, which may then acylate nucleophiles after polymer removal (
Ebara Research Co. Ltd., Fujisawa-shi, Japan