Preparation and use of alkylating agents

Methods of alkylating target compounds are disclosed. The alkylating agent can be radiolabelled. In some instances, the alkylating agent is synthesized and then reacted with a target compound without an intervening purification step. The method comprises a) 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 b) directly reacting said alkylating agent with a target compound comprising an alkylation reactive group under conditions suitable for the alkylation of said target compound.