A racemic β-lactam [1-tert-butyldimethylsilyl-4-phenylthioazetidin-2-one (3)] was subjected to kinetic resolution using a homochiral lithium amide base [lithium (R,R)-bis(1-phenylethyl)amide (2)]. Reaction of the so-formed non-racemic carbanion with chlorotrimethylsilane gives an α-silylated β-lactam product 6 in up to 72% enantiomeric excess, whilst reaction with acetaldehyde allows access to α-acetyl β-lactam 7, an intermediate in the synthesis of thienamycin, in similar optical purity.