Abstract:
We have devised simple, facile, and greener methods in the synthesis of several new chiral amines on silica surfaces. Several of these amines have the pyridyl, furyl, and other moieties in their molecular structures, thus affording additional ligands for coordination with other chiral molecules. We have also synthesized amines with ortho substituents which afford steric hindrance to the reactions. In all cases the reactions gave quantitative yields of the products. In the synthetic procedure, typically 2.0 g of activated silica were added to 10 mL of an ethereal solution of equimolar quantities (2.0x10-3 mol) of an aldehyde and a primary chiral amine. The flask was equipped with a stirring bar and a drying tube. The mixture was stirred briefly and allowed to stand for 15 minutes to 30 minutes at room temperature. Completion of the reaction to the imine stage was monitored by GC-MS. The reduction step was carried out in the same pot by adding 0.15 g of sodium borohydride, followed by the addition of a few drops of water, while cooling the flask in an ice bath. The flask was briefly stirred upon each addition of water. Progress of the reduction was monitored by GC-MS. Purified products were analyzed by IR, GC, GC-MS, and proton and C-13 NMR, and by polarimetry.