Synthesis of Polymer-Bound 5- 2-Bromoacetyl pyrroles

In the first step, Rink amide AM PS Resin was acetoacetylated with diketene. Treatment with primary amines resulted in polymer-bound enaminones which then underwent a Hantzsch reaction [30] with l,4-dibromo-2,3-butanedione under formation of 5-(2-bro-moacetyl)pyrroles which could be cleaved from the resin with 20 % TFA/CH2C12. 

A wide range of amines can be used in the synthesis of these polymer-bound substrates, except for amines with nucleophilic side chains. This is due to the fact that 1,4-dibromo-2,3-butanedione is a strong alkylating agent. Amines with hydroxy functionalized side chains can be incorporated into the synthesis, whereas amines with tertiary amino groups in the side chain, for example N-(2-aminoethyl)morpholine, are not suitable due to byproduct formation. 

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