To efficiently obtain the subject compound useful as an antibiotic substance excellent in antimicrobial activities and stability in a short process by reacting an α,β-unsaturated ester with a sulfenyl chloride compound.

A compound represented by formula I [R is H or a trialkylsilyl; TBDMSO is (R)-t-butyldimethylsilyloxy] is reacted with a sulfenyl chloride compound (e.g. methanesulfenyl chloride) to afford a substituted carbapenem represented by formula II. The reaction is carried out in a solvent such as methylene chloride at -30 to +50°C by using 2.4-18 equiv. sulfenyl chloride compound. Furthermore, (1R,5S,6S)-6-[1-(R)-t-butyldimethylsilyloxyethyl]-3- ethoxycarbonyl-1-methyl-2-methylthio-carbapenem, etc., are cited as the compound represented by formula II.