Bioorthogonal reaction suitable for click/unclick applications

A compound having a structure represented by formula II or III:

• or a pharmaceutically acceptable salt or stereoisomer thereof,
• wherein:
• each X is independently CR9R9′, NR9, O, S, C(O), S(O), or SO2, wherein the ring system contains 0-3 heteroatoms;
• R9 and R9′ are independently hydrogen or a substituent;
• Y is absent or
• A2 is an active moiety;
• R4 is hydrogen, a substituent or a linking group bound to an
• group, or
• R4 and R5, together with the carbon atom to which they are attached, form a carbocyclyl or a heterocyclyl, wherein R4 is also bound to an
• group;
• R5 is hydrogen or an electron withdrawing group;
• R6 is hydrogen, a π-electron donor group, or a linking group bound to an
• group;
• R7 and R7′ are independently hydrogen or an electron withdrawing group, or
• R7 and R7′, together with the carbon atom to which they are attached, form C(O);
• R8 is hydrogen, a substituent, or a linking group bound to an
• group;
• and
• n is 1, 2, or 3,
• provided that the compound contains an
• group.

A compound having a structure represented by formula IV or V:

• or a pharmaceutically acceptable salt or stereoisomer thereof,
• wherein:
• R1′ is a linking group;
• R1 is absent, or
• R1 and R2, together with the nitrogen atom to which they are attached, form a heterocyclyl;
• R2 is optionally substituted (C1-C8) alkyl, —C(O)R″, —C(O)OR″, —C(O)NR″R″, —S(O)R″, —S(O)2R″, (C3-C10) carbocyclyl, 4- or 7-membered heterocyclyl, or a substituted polyethylene glycol chain, wherein each R″ is independently hydrogen, (C1-C6) alkyl, (C3-C10) carbocyclyl, 4- or 7-membered heterocyclyl, and wherein said alkyl, carbocyclyl, or heterocyclyl is optionally substituted;
• each X is independently CR9R9′, NR9, O, S, C(O), S(O), or SO2, wherein the ring system contains 0-3 heteroatoms;
• R9 and R9′ are independently hydrogen or a substituent;
• A1 is an active moiety;
• Y is absent or
• A2 is an active moiety;
• R4 is hydrogen, a substituent or a linking group bound to
• or
• R4 and R5, together with the carbon atom to which they are attached, form a carbocyclyl or a heterocyclyl, wherein R4 is also bound to
• R5 is hydrogen or an electron withdrawing group;
• R6 is hydrogen, a π-electron donor group, or a linking group bound to
• R7 and R7′ are independently hydrogen or an electron withdrawing group, or
• R7 and R7′, together with the carbon atom to which they are attached, form C(O);
• R8 is hydrogen, a substituent, or a linking group bound to
• and
• n is 1, 2, or 3;
• provided that the compound contains at least one
• group.

A process of preparing a compound of formula IV:

• comprising reacting a compound of formula I:
• with a compound of formula II:
• or
• a process of preparing a compound of formula V:
• comprising reacting a compound of formula I:
• with a compound of formula III: