Stevens rearrangement

The Stevens rearrangement is a name reaction in organic chemistry, which was named after Thomas Stevens Stevens. Her an organic group R (alkyl, allyl, benzyl) is of a four- bonded nitrogen atom shifted ( a quaternary ammonium ion ) to an adjacent carbon atom, under the action of a base, which is an electron -withdrawing group such as a ketone, an ester group or a aryl group bears ( electron- withdrawing groups are often referred to as EEC "electron withdrawing group " means ). The same reaction also takes place with sulfonium salts.

Mechanism

The rearrangement in this case runs with retention of stereochemistry of the migrating substituent, which argues against a concerted [ 1,2] - migration, since this inversion of the stereochemistry of the migrating group would occur. It is therefore assumed a free radical mechanism in which resulting from the homolytic dissociation of the bond, the two radicals in the " solvent cage " remain close to each other as fast recombination occurs to the product. In addition to the radical course of an ion -pair mechanism is discussed, which proceeds via a heterolytic cleavage.

The mechanism is analogous to ammonium and sulfonium salts, here, an ammonium salt is used exemplarily. The base is an example of a amide anion. First, it is mixed with a quaternary ammonium salt having a methyl group 1 amide anion, whereby the methylene group is deprotonated and obtained 2 molecule. The radical route (above), the bond between the nitrogen atom and a radical cleaves homolytically and there is the radical 3, which has, due to the resonance of two boundary structures. In addition, a radical is formed This rest radical residue attaches to the carbon atom of the radical to 3 so that the final product 5 is produced.

When ionic reaction course ( below) the charge deposited on the carbon so that a double bond between the carbon and the nitrogen is produced and the bond between the nitrogen and one of its residues butylbromide. This creates an iminium ion, which can be represented as different mesomeric structure as carbenium ion 4. Furthermore, results in a negative geladender Rest This rest now settles for a nucleophilic attack on the carbon atom of the carbenium ion to this at. Thus, the final product 5 is obtained in the form of an amine.