Hydrogen/metal permutations

Halogen/metal permutation and hydrogen/metal permutation (usually apostrophed as "metalation") dominate the interconversion methods. They employ organoalkali reagents such as phenyllithium, methyllithium, -butyllithium, iec-butyllithium, or the superbasic LIC-KOR mixture. However, even if commercial, these reagents have to be made beforehand. The reaction of a chloro- or bromo-substituted hydrocarbon with lithium, sodium, or magnesium offers a standard entry to them. Thus, ultimately one always has to revert to the metal. 

An organometallic reagent M-R may react with a hydrocarbon H-R under hydrogen/metal permutation to generate a new organometallic intermediate M-R. Being subject to a variety of factors, the countercurrent metal and proton transfer process can proceed more or less rapidly. To make it occur at all, the substrate H-R must be more acidic than the resulting hydrocarbon H-R. 

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