A new synthetic method for the reduction of imines by samarium-induced reaction †

Synthesis of secondary amines is an attractive area of research. Several groups have described the synthesis of secondary amines using various reagents. t For example; recently, Lopez and Fu described the synthesis of secondary amines by tin-catalyzed reduction of imines . However, the reduction of the tmlnes either by catalytic hydrogenation or borohydride type reagents is still the best-established method to produce secondary amines in reasonably good yield. Unfortunately, the catalytic hydrogenation reaction is not environmentally friendly because of its fire-sensitive catalysts, such as Pd-C and Raney Ni. The alternative of using borohydrides is not, in general, effecti ve fo r the reducti on of sterically hindered imines, and mi xtures of isomeric amines result if cyclic imines are substituted. Alternat ive methods that can overcome these drawbacks are necessary. One possibility is to use lanthanide reagents, which have witnessed a tremendous increase in use in organic synthesis. Of these lanthanides, samarium diiodide has been the most attractive reagent. The efforts in this area substantiate the unique role samarium diiodide can play in promoting reactions that are very difficult to accomplish by other available reagents. The success of the samarium dii odide reaction, however, depends in many cases on the presence of a strong base, such as hexamethylphosphoramide (HMPA). Furthermore, the storage of samarium diiodide is difficult because it is very sensitive to ox idation in air. On the other hand, samarium metal is stable in air, and has a strong