Polymer-supported 4-aminopyridines

The nitropyridines can be reduced to the corresponding aminopyridine and several new methods have been developed to achieve this transformation. 3-Nitropyridine is reduced in excellent yield by the mixed borohydride prepared from 1 equiv of ZrCU and 4 equiv of NaBFLi in THF under reflux <2000SL683>. 3-Nitropyridines may be reduced to the aminopyridine using sodium hydrosulfite in THF/H20 at room temperature <2005JME5104>. 2-Nitropyridine can be reduced to the amine in near quantitative yield by transfer hydrogenation in the presence of 10% Pd/C and recyclable polymer-supported formate, prepared from aminomethylpolystyrene resin and ammonium formate <2005SC223> (Equation 64). The resin is easily recovered by filtration and may be used up to 10 times. 

Oxidation of alcohols. The pernithenate salt is an excellent catalyst for aerobic oxidation of alcohols to aldehydes and ketones in the presence of 4A molecular sieves. The use of a polymer-supported ammonium perruthenat is perhaps an improvement, with good discrimination in the oxidation in favor of primary alcohols. Another versioif specifies a system containing CuCl and 2-aminopyridine also. 

Synthesis of Pyrimidine Derivatives. In 2002, Lam and coworkers reported the use of polystyrene/1 % divinylbenzene sodium sulfinate 43 as solid-phase support for the synthesis of pyrimidine derivatives (Scheme 12.33)." Resin 43 in NBU4I/KI/DMF was allowed to react with l,3-dichloropropane-2-one at room temperature to yield the polymer-supported a-haloketones 159. Treatment of resin 159 with substituted aminopyridines in anhydrous DME yielded the imidazo[l,2-a]pyridine resin 160. Alkylation of resin 160 occurs selectively with cw-epoxide and not the trans isomer to give resin 161, which could be... 

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