PURPOSE: To obtain a 4-substituted azetidinone derivative useful as an intermediate for carbapenem-based compounds industrially and advantageously by reacting an azetidinone derivative with an ester or a thiol ester compound in the presence of a specific halogen-containing organometallic compound and a base.

CONSTITUTION: An azetidinone derivative of formula I [R is H or readily eliminable N-protecting group; R1 is (protected) hydroxyl group, (substituted) alkyl, etc.; Z is eliminable group] is reacted with an ester or thiol ester compound of formula II [R2 is H or alkyl; R3 is (substituted) phenylene; X is O or S; A is (substituted) alkylene, (substituted) o-phenylene, (substituted) toluene-α, 2-diyl or (substituted) o-xylene-α, α'-diyl; B is SO2, C=O or C=S] in the presence of a compound of formula III [M is metal atom; Hal is halogen; R4 is lower alkyl, lower alkoxy, (substituted) phenoxy, etc.; n and m are 0 or 1-5] and a base to give the objective 4-azetidinone derivative of formula IV.