Stereoselective synthesis of a key intermediate of sanfetrinem by means of a chelated tin(IV) enolate

摘要

(2S)-2-Methoxycyclohexanone [(2S)-6], reacts with the 4-acetoxyazetidinone 3a in the presence of SnCl_4 and a tertiary amine base (Such as N,N-diisopropylethylamine) to give the ketoazetidinone 5(a key intermediate in the synthesis of the broad-spectrum antibiotic sanfetrinem 2a) with high yield and diastereoselectivity. Low-temperature NMR studies of the reaction indicated the formation of a 1:1 chelate complex 11 between SnCl_4 and (2S)-6 which, on addition of the base is transformed into the highly reactive chelated tin enolate 12.