PURPOSE: To produce a nitron compound to be an intermediate for producing various useful organic compounds represented by carbapenem-based compounds in high selectivity by using a readily available compound as a raw material.

CONSTITUTION: A compound expressed by formula I [R1 is lower alkyl, aryl, ar(lower)alkyl, hydroxy(lower)alkyl substitutive with aryl or protected hydroxy(lower)alkyl substitutive with aryl; either of R2 and R3 is lower alkyl, aryl or ar(lower)alkyl and the other is H, lower alkyl or ar(lower)alkyl or either thereof may be condensed with R1 to form lower alkylene; R4 is H, OH or acyloxy] or its salt at the carboxyl group is made to react with a catalyst (e.g. a metallic oxide), an oxidizing agent (e.g. a peroxide substance) and a base to afford the objective (4R)-4-(tertiary butyldimethylsilyloxy)-1-pyrroline-N- oxide expressed by formula II.