Dimroth rearrangement

Otto Dimroth (1872–1940)

As Dimroth rearrangement is a rearrangement reaction of exo - and endo -cyclic heteroatoms in heterocyclic designated rings. The term became a name reaction in organic chemistry in the 1960s . Exo - and endo -Cyclic hetero atoms (mainly nitrogen atoms) in this case change their position. The reaction was first observed and published in 1909 by the German chemist Otto Dimroth (1872–1940).

1 H -1,2,3-triazoles can also undergo the Dimroth rearrangement. The reaction usually takes place on six-membered rings, but it can also be carried out on five-membered rings.

mechanism

Under basic conditions, a pyrimidine derivative reacts to form a rearranged pyrimidine derivative. In the following example, a nitrogen atom (more precisely: NR) from the ring has changed position with the nitrogen atom of the imine group:

R = alkyl radical , aryl radical or hydrogen atom .

The hydroxide ion attacks the carbon atom in position 6 of the pyrimidine derivative 1 . The anion 2 is formed which rearranges to the enol intermediate 3 . A [1,7] proton transfer produces alcoholate 4 , which forms a carbonyl group through electron rearrangement. The imidamide intermediate 5 is then formed via an intermediate stage . The amide ion 6 can then be formed from 5 by renewed electron pair rearrangement , which then carries out a nucleophilic attack on the carbon atom of the carbonyl group with the negatively charged nitrogen atom , whereby the heterocyclic alcoholate intermediate 7 is formed. The alcoholate 7 is protonated to the alcohol 8 by water . The pyrimidine derivative 9 is finally formed by splitting off water .

Examples

With the help of an example, the broad applicability of the Dimroth rearrangement will now be illustrated.

Due to the Dimroth rearrangement, even more complex residues can change their position in the molecule. This is shown here using a pyrimidine derivative on which a chlorinated phenyl radical is rearranged:

As already mentioned above, 1,2,3- triazoles can also undergo a Dimroth rearrangement. This is shown in the following example. Ar denotes an aryl radical :

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

Web links

• Eugene Lieber, Tai Siang Chao, CN Ramachandra Rao: 1,4-Diphenyl-5-amino-1,2,3-triazole AND 4-Phenyl-5-anilino-1,2,3-triazole In: Organic Syntheses . 37, 1957, p. 26, doi : 10.15227 / orgsyn.037.0026 ; Coll. Vol. 4, 1963, p. 380 ( PDF ).

Individual evidence

1. ↑ Otto Dimroth: About intramolecular rearrangements. Rearrangements in the series of 1, 2, 3-triazole. In: Justus Liebig's Annals of Chemistry. 364, No. 2, 1909, pp. 183-226, doi : 10.1002 / jlac.19093640204 .
2. ↑ Otto Dimroth, Walter Michaelis: Intramolecular rearrangement of the 5-amino-1,2,3-triazole. In: Justus Liebig's Annals of Chemistry. 459, No. 1, 1927, pp. 39-46, doi : 10.1002 / jlac.19274590104 .
3. ↑ Otto Dimroth: About a synthesis of derivatives of 1.2.3-triazole. In: Reports of the German Chemical Society. 35, No. 1, 1902, pp. 1029-1038, doi : 10.1002 / cber.190203501171 .
4. ^ ^{A b} Z. Wang: Comprehensive Organic Name Reactions and Reagents, 3 Volume Set . Volume 1, John Wiley & Sons, Hoboken, New Jersey 2009, ISBN 978-0-471-70450-8 , p. 906.
5. ^ Z. Wang: Comprehensive Organic Name Reactions and Reagents, 3 Volume Set . Volume 1, John Wiley & Sons, Hoboken, New Jersey 2009, ISBN 978-0-471-70450-8 , p. 905.
6. ^ Reto W. Fischer and Marian Misun: Large-Scale Synthesis of a Pyrrolo [2,3-d] pyrimidine via Dakin-West Reaction and Dimroth Rearrangement . In: Organic Process Research & Development . tape 5 , no. 6 , 2001, p. 581-586 , doi : 10.1021 / op010041v .