n - tert - butoxycarbonyl - 2 - pyrrolidinones represented by the following formula . in the formula , r1 , r2 , r3 , r4 , r5 and r6 independently represent a hydrogen atom , a halogen atom , a cyano group , a linear , branched or cyclic alkyl group having 1 to 10 carbon atoms , which may have a substituent , a linear , branched or cyclic alkenyl group having 2 to 10 carbon atoms , which may have a substituent , or the like , r1 and r2 may be linked to form a & gt ; c ═ o group along with the carbon atom to which both are attached , r3 and r4 may be linked to form a & gt ; c ═ o group along with the carbon atom to which both are attached , r5 and r6 may be linked to form a & gt ; c ═ o group along with the carbon atom to which both are attached , or any two among r1 , r2 , r3 , r4 , r5 and r6 may be linked to form a polymethylene group having 1 to 4 carbon atoms which may have a substituent .