Polymeric scavenger

Bis(indolyl)nitroethanes are obtained readily in 7-10 min in high yields (70-86%) on fine TLC-grade silica gel (5-40 pm) by Michael reaction of 3-(2 -nitrovinyl) indole with indoles. The same reaction reported requires 8-14 h for completion at room temperature [77]. Several functionalized resins have been prepared from Merrifield resin via a MW-assisted procedure that utilized mixed solvent system to facilitate the swelling of resins and coupling with microwaves [78], These resins can function as solid supports or polymeric scavengers in solid phase synthesis. 

The synthetic utility of ion exchange resins in combinatorial chemistry has been demonstrated by the use of a basic polymeric base PTBD (l,5,7-triazabicydo[4.4.0]dec-5-ene) 26 in a series of O- and N-alkylation experiments (Scheme 7) [15]. For example, deprotonation of the phenol 27 with this polymeric base PTBD 26 gave the ionic polymeric species 28 which contained the more nucleophilic phenolate. Addition of the 2-bromo aryl ketone 29 gave the aryl ether 30 in reasonable yield and in high purity (Scheme 7). The basic polymeric scavenger PTBD 26 removed all the unwanted HBr produced within the reaction mixture (in the form of 31) and advantageously eliminated the need for an aqueous extractive work-up procedure. 

Other representative examples in which polymeric scavenger reagents are used, include L. A. Thompson and J. A. Ellman, Chem. Rev. 1996, 96, 555-600 ... 

Polymeric scavenger reagents in organic synthesis (including synthesis of heterocycles) 01EJO1213. 

---