β-Lactam Ring Opening in the Reformatsky Reaction of (3R,4R)-4-Acetoxy-3-((1R)-1-{[tert-butyl(dimethyl)silyl]oxy}ethyl)azetidin-2-one with Ethyl 4-Bromo-3-oxopentanoate

The Reformatsky reaction of (3 R ,4 R )-4-acetoxy-3-((1 R )-1-{[ tert -butyl(dimethyl)silyl]oxy}ethyl)­azetidin-2-one with ethyl 4-bromo-3-oxopentanoate gave product of replacement of the acetoxy group by C 2 -carbanion of the β-keto ester, which underwent retro-aza-Michael reaction with opening of the azetidinone ring with the formation of acyclic ethyl (2 Z ,4 S ,5 R )-4-carbamoyl-5-{[ tert -butyl(dimethyl)silyl]oxy}-2-pro­panoyl­hex-2-enoate. Treatment of the latter with di- tert -butyl dicarbonate afforded hex-3-enoate and dihydro­pyridin-6-one derivatives.