NEW MATERIAL:A compound shown by the formula I {R1 is CH= CHNHCOCH3, or CH2CH2NHR3 [R3 is H, CH3, or group shown by the formula II (R4 and R5 are H, lower alkyl, phenyl, benzyl, or diphenylmethyl)]; R2 is ester-protecting group of carboxyl group; n is 1 or 2}.

EXAMPLE: (5R,6R)-3-(2-Acetaminoethyl)sulfinyl-6-[(R)-1-fluoroet-hyl]-7-oxo-1-azabi cyclo[3,2,0]hept-2-ene-2-carb-oxylic acid p-nitrobenzyl ester.

USE: A synthetic intermediate for producing a 8-fluorocarbapenem derivative.

PREPARATION: For example, a compound shown by the formula XI (R1-1 is R1 is, etc.) is esterified, protected, and reacted with diethylaminosulfur trifluoride, etc., so OH at the 8-position is replaced with F to give a compound shown by the formula XIV, which is subjected to S-oxidation to give a compound shown by the formula I.