A compound having the general formula shown below: where R1-6 are independently selected from the group consisting of an electron withdrawing group, an alkyl group, an aryl group, hydrogen, a heteroaryl group, and a five or six member ring structure formed from the R1 and R2 pair, the R3 and R4 pair, the R4 and R5 pair, or the R5 and R6 pair; R7 is a substituted or unsubstituted aryl group; and Y is a nucleophile.