Methods of alkylating target compounds are disclosed. The alkylating agent can be radiolabeled. In some instances, the alkylating agent is synthesized and then reacted with a target compound without an intervening purification step. The method comprises synthesizing an alkylating agent having the formula: X—(CR1R2)aCR3R4-LG wherein, a is 0, 1, 2 or 3, R1, R2, R3 and R4 are independently H, X or alkyl, X is a halogen or a label, with the proviso that at least one X is a halogen, LG is a leaving group; and directly reacting said alkylating agent with a target compound comprising an alkylation reactive group under conditions suitable for the alkylation of said target compound.