Polymer-supported reagents carboxylic acid synthesis

A one-step synthesis of 1,3,4-oxadiazoles from readily available carboxylic acids and acid hydrazides was mediated by the polymer-supported reagent... 

In related work, rapid synthesis of 1,2,4-oxadiazoles was achieved on polymer-supported reagents [109]. Two independent pathways were used to prepare these heterocycles from carboxylic acids and amidoximes under the action of microwave irradiation. In accordance with the conventional method using HBTU and N,N-diisopropylethylamine (DIEA) for synthesis of this heterocycle, a method utilizing polymer-supported bases was employed. The use of PS-BEMP in the presence of HBTU proved to be beneficial in the microwave procedure. Heating for 15 min in acetonitrile at 160 °C furnished high yields for a series of substrates. 1,2,4-Oxadiazoles can also be synthesized from carboxylic acid chlorides. Because these... 

In summary, the polymer-bound oxoammonium reagent was highly efficient in polymer-supported oxidations of various alcohols and was capable of cleanly converting chemically diverse compound collections. No overoxidation to carboxylic acids was observed. It is obvious that this reagent shall be of great value in polymer-supported transformations in solution, in automated parallel synthesis operations, and in flow-through reactors in up-scaled production processes. 

The field of organic chemistry has seen the most extensive use of polymeric materials as aids in effecting chemical transformation and product isolation. Insoluble polymer supports have been used as handles to facilitate these functions. As chemical reagents can be bound to an insoluble polymer carrier and used in organic synthesis [117,118], polymer-bound reagents can also be used to assist in the purification step of solution-phase reactions [119,120]. The latter are known as scavenger resins. These are added to the reaction mixture upon completion of the reaction in order to quench and selectively bind to the unreacted reagents or by-products. The polymer-bound impurities are then removed firom the product by simple filtration to obtain pure compounds. For example, aminomethylated poly(styrene-co-divinyl benzene) can be used to remove acid chlorides, sulfonyl chlorides, isocyanates, thiocyanates, and proton. Similarly, 2-Chlorotrityl resins have been developed for the attachment of carboxylic acids, alcohols. 

Solid-phase peptide synthesis (SPPS) (Section 24.7D) A method of peptide synthesis in which the peptide is synthesized on a solid support, one amino acid residue at a time. The first amino acid of the peptide is bonded as an ester between its carboxylic acid group and a hydroxyl of the solid support (a polymer bead). This is then treated with a solution of the second amino acid and appropriate coupling reagents, creating a dipeptide. Excess reagents, byproducts, etc. are washed away. Further linkages are synthesized in the same manner. The last step of the synthesis is cleavage of the p>eptide from the solid support and purification. 

Tartar and co-workers [18] reported the synthesis of polymer supported 1-hydroxybenzotriazole (Figure 7). Reaction of the reagent with a carboxylic acid... 

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