COPPER-CATALYZED AMINATION OF SILYL KETENE ACETALS WITH N_CHLOROAMINES

Abstract

A copper(I)/2,20-bipyridyl complex catalyzes an amination reaction of silyl ketene acetals with N-chloroamines, presenting a new preparative method of R-amino esters. Amines intrinsically possess a nucleophilic property. Their nucleophilic substitution reactions present con- ventional preparative methods of substituted amines. Transition-metal-catalyzed cross-coupling reactions of aryl halides with amines are also powerful methods for the formation of C N bonds.1 An alternative pathway to substituted amines has recently become available by the use of electrophilic amination reagents together with nu- cleophilic organometallic species.2 For example, Johnson and co-workers have reported their pioneering research on copper- and nickel-catalyzed amination reactions of diarylzinc compounds using N-hydroxyl(dialkyl)amine derivatives as the amination reagent.2e,f N-Chloroamines are also promising amination reagents with their easy availability3 as well as high reactivity.4 Jarvo and co- worker reported a nickel-catalyzed amination reaction of diarylzinc compounds with N-chloro(dialkyl)amines, which formed tertiary anilines.2k Similarly, secondary ani- lines are produced by the reaction of in situ-generated N-chloro(monoalkyl)amines with arylmagnesium reagents in the presence of an excess amount of titanium(IV) isopropoxide.2l,5 Furthermore, transition-metal-catalyzed direct C H amination reactions of aromatic compounds with N-chloro(dialkyl)amines have been developed byMiura,6 Yu,7 and Glorius.8,9 It is also possible to intro- duce an amino group at the R-positions of carbonyl compounds by the reaction of their lithium enolates with N-chloroamines,10,11 although the substrate scope is limited probably due to the strongly basic reaction conditions as well as competing side reactions such as a chlorina- tion reaction. We envisaged that an analogous amination reaction of carbonyl compounds would become feasible under milder conditions if it is assisted by transition-metal catalysts. Herein we report that a copper(I)/2,20-bipyridyl complex successfully catalyzes an amination reaction ofsilyl ketene acetals with N-chloroamines to afford R-aminoesters.