Patent ID: 7145000

Claim:
A compound of the following formula wherein R represents Br, I or R 1 —SO 3 , wherein R 1 is an unsubstituted or substituted C 1 –C 5 -alkyl group, or an unsubstituted or substituted phenyl group; X is O or NR″, wherein R″ is a usual protective group for N; and R′ represents hydrogen, halogen, a substituted C 1 –C 7 -alkyl group, an unsubstituted C 1 –C 7 -alkyl group, a substituted C 2 –C 7 -alkenyl group, an unsubstituted C 2 –C 7 -alkenyl group, a substituted C 2 –C 7 -alkynyl group, or an unsubstituted C 2 –C 7 -alkynyl group; wherein the moiety substituted on the C 1 –C 5 -alkyl group is an electron-withdrawing group, and wherein the moiety substituted on the phenyl group is a C 1 –C 5 -alkyl group or an electron-withdrawing group.