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Solid-phase synthesis has developed rapidly in recent years. It is widely used in the pharmaceutical industry for the syntheses of biooligomeric molecules, some small molecules, and combinatorial chemistry as well. Polymeric reagents are currently playing an important role in solid-phase synthesis. A polymeric reagent, polymer-supported diphenylphosphoryl azide (DPPA), was prepared from phenol resin. The conversion from phenol resin to polymer-supported DPPA is about 80% efficient. This polymer-supported version of DPPA is useful due to its lower toxicity, moisture tolerance and ease of workup after reaction. The synthetic application of this solid-phase reagent was explored by conversion of a variety of carboxylic acids to urethanes and ureas through Curtius rearrangement reactions. Carboxylic acids bearing different functional groups (aromatic, aliphatic and heterocyclic carboxylic acids) were subjected to the reactions. The corresponding products were isolated with satisfactory yields. By using this polymer-supported DPPA, oxazolidinone, imidazolidinone and thiazolidinone derivatives were also successfully prepared from carboxylic acids with different reactive functional groups in the ¦Â position, such as alcohols, thiols and primary or secondary amines. The desired compounds were obtained in good yields via Curtius rearrangement and subsequent intramolecular cyclization. This polymer-supported DPPA was further used in the divergent syntheses of polyurethane dendrimers. Purification became easier in the synthesis because a simple filtration could remove DPPA and all other phosphorous derivatives. Four molecules with different sizes, branching numbers and polarity were used as core molecules. Solvent selection was also considered in the synthesis. All the molecular weights of these polyurethane dendrimers were determined by MALDI-TOF Mass Spectra, which established the formation of the dendrimers. The diameters of all polyurethane dendrimers were calculated using Chem3D Ultra based on PM3 (semi-empirical level) optimized structures. Other solid-phase reagents were studied as well. Polymer-bound organosilicon reagents, such as silyl ketene, silyl azide and silyl cyanide, were converted from a polymer-bound trialkylsilyl chloride. Applications of these organosilicon reagents were carried out using classical organic reactions. Solid phases were compared between polystyrene resin, Si-dimethylsilyl derivatized silica gel and TentaGel-S-Br. The feasibility of further development of these reagents was established. |
