Sequential nucleophilic addition/1,2-rearrangement of N-iminolactam: A ring-contractive strategy for the synthesis of 2-acyl pyrrolidines

Synthesis of Unsymmetrical Ketones Using Chelation-Controlled Sequential Substitution of N-Triazinylamide/Weinreb Amide by Organometallic Reagents

“…Each product could be isolated by column chromatography on silica gel using hexane/ethyl acetate (3/1 to 2/1) as an eluent. Structures of the products, Weinreb amide and ketone, were confirmed by a comparison of the 1 H NMR spectrum with that of authentic samples . Yields of Weinreb amide 4a and symmetrical ketone 5a were determined by a comparison of integral values with those of 1,1,2,2-tetrachloroethane as an internal standard in the 1 H NMR using CDCl 3 as a solvent.…”

“…An amide possessing an N -methoxy- N -methylamino (MMA) group called the Weinreb amide is a representative (Figure , upper) . Other chelating groups such as carbonyl, imino, and sulfonyl groups were found to stabilize the adduct intermediates leading to ketones; however, the amides used in most reactions are limited to cyclic amides (lactams and imides). Recently, it was demonstrated that the 1-pyrazolyl group is a good leaving group in the synthesis of ketones using Grignard reagents …”