PS-DMAP

A polystyrene supported version (PS-DMAP) is commercially available. 

PS-DMAP Polystyrene-hound dimethylaminopyridine Rfs Perfluorooctyl, CsFu... 

A one-pot synthesis of thiohydantoins has been developed using microwave heating [72]. A small subset of p-substituted benzaldehydes, prepared in situ from p-bromobenzaldehyde by microwave-assisted Suzuki or Negishi reactions, was reacted in one pot by reductive amination followed by cyclization with a thioisocyanate catalyzed by polystyrene-bound dimethyl-aminopyridine (PS-DMAP) or triethylamine, all carried out under microwave irradiation, to give the thiohydantoin products in up to 68% isolated yield (Scheme 16). 

In a separate study, Ohberg and Westman applied the same PS-DMAP in a one-pot microwave-induced base-catalyzed reaction of N-aryl and N-alkyl amino acids (or esters) and thioisocyanates for the library synthesis of thiohydantoins (Scheme 7.115) [136]. Thiohydantoins are of interest due to their ease of preparation and the range of biological properties associated with this heterocyclic ring system. The use of PS-DMAP as the base in this reaction gave slightly lower yields compared to when triethylamine (TEA) was used, but it resulted in a cleaner reaction mixture and an easier purification procedure. Cyclizations of a number of N-substituted... 

The method developed by Garegg et al. [14] to form benzylidene acetals was modified by Oscarson et al. [5], who treated compound 9 with benzal bromide and N-(methylpolystyrene)-4-(methylamino)pyridine (PS-DMAP) in acetonitrile under microwave irradiation conditions to form the 4,6-O-benzylidene derivative 20 (83%) after 5 min (Scheme 12.9). 

Selective protection of dihydropyrimidinones has been used in a novel approach to improve the synthesis of valuable Biginelli compounds with different substitution patterns [130]. This procedure has been successfully catalyzed by polymer-supported NjN-dimethylaminopyridine (PS-DMAP) (Scheme 16.85). This micro-... 

The microwave-assisted one-pot three-step synthesis of thiohydantoins has been studied together with a polymer-supported catalyst and/or reagent [55]. Cyclization of a number of AT-substituted amino acids of type 50 and thioiso-cyanates 51 has given satisfactory yields within 5 min at 170 to 180 °C (see Scheme 29). Polymer-supported dimethylaminopyridine (PS-DMAP) 52 has been utilized as a supported base herein to catalyse the reaction however, in most cases the yield was comparatively lower to the use of triethylamine (TEA). PS-DMAP also assisted in simplifying the purification. 

Microwave-assisted selective protection of dihydropyrimidinones has also been afforded using PS-DMAP. The microwave-induced selective AT3-acylation has been applied to a diversely substituted dihydropyrimidinone scaffold with 30-97% isolated yield within 10-20 min of microwave irradiation (see Scheme 30) [56]. 

Using these methods we more recently reported the synthesis of another isoquinoline alkaloid, (-)-norarmepavine (Scheme IS.IO). " This was accomplished by coupling the amine 26 with the ester 27 to give an intermediate amide (28). This was best done using focused microwave irradiation under solvent-free conditions. Next, 28 was converted to a Bischler-Napieralski product by using a combination of triflic anhydride and PS-DMAP. This was followed by scavenging with polymer-supported A(-(2-aminoelhyl)aminomethyl polystyrene to remove any excess anhydride. The intermediate triflate was then converted to the free base 29 with PS-BEMP (7), mentioned earlier. Finally, a proline-derived reductant... 

It is commercially available in 0.04mmol impregnated tablets, and a polystyrene supported version (PS-DMAP) with a loading of 3.0mmol/g is also available for recyclable acylation pirrposes. 

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