Dimroth rearrangement

As a Dimroth rearrangement rearrangement reaction of exo -and endo- cyclic hetero atoms is referred to in heterocyclic rings. The term was coined in the 1960s to a named reaction in organic chemistry. Exo-and endo - cyclic hetero atoms (mostly nitrogen atoms) change this position. The reaction was for the first time in 1909 by the German chemist Otto Dimroth - observed and published (1872, 1940 ).

Also 1H-1 ,2,3- triazoles prepared to take the Dimroth rearrangement. Usually the reaction proceeds at six-membered rings, but they can also be performed in the five-membered rings.

Mechanism

Under basic conditions, a pyrimidine derivative reacts to a rearranged pyrimidine derivative. In the following example this is a nitrogen atom (more precisely: NO ) has changed position to the nitrogen atom of the imine group in the ring:

The hydroxide attack at the 6-position of the pyrimidine derivative 1 at the carbon atom. In this case, the anion 2 which the enol intermediate 3 is rearranged. Through a [1,7 ] - proton transfer, the alkoxide 4, which forms a carbonyl group by electron rearrangement occurs. About an intermediate then forms the imide amide intermediate 5 from 5 can then form by re- electron pair rearrangement, the amide ion 6, which now performs a nucleophilic attack on the carbon atom of the carbonyl group with the negatively charged nitrogen atom, to form the heterocyclic alkoxide intermediate 7 forms. The alcoholate 7 is protonated by water to the alcohol 8. Elimination of water finally the pyrimidine derivative 9 produced

Examples

With the aid of an example of the wide applicability of the Dimroth rearrangement is now to be explained here.

Through the Dimroth rearrangement, more complex radicals can change their position in the molecule. This example is shown here are based on a pyrimidine derivative, to which a phenyl radical is redistributed chlorinated:

Also, 1,2,3- triazoles, as already mentioned above undergo a Dimroth rearrangement. This is illustrated in the following example. Ar denotes an aryl group here:

The triazoles have to bear an amino group in the 5-position. After ring opening to a diazo intermediate, and a CN- bond rotation, a rearranged triazole is obtained.