Tiffeneau–Demjanov rearrangement

The Tiffeneau ring expansion (also Tiffeneau Demianov reaction, rearrangement or ring expansion ) is a name reaction in the field of organic chemistry and describes the synthesis of ring-expanded cyclic ketones starting from 1- Aminomethylcycloalkoholen ( β -amino alcohol ).

Overview reaction

The reaction was detected in two steps. 1901 observed the Russian chemist Nikolay Yakovlevich Demyanow (Russian: Николай Яковлевич Демьянов; 1861-1938 ) that arise in the diazotization of Aminomethylcycloalkanen cyclic alcohols by ring expansion. 1937 published Tiffeneau (1873 - 1945), Weill and Tchoubar their results for diazotization of 1- Aminomethylcycloahexanol, where Cycloheptanone arises:

The Tiffeneau Demianov reaction belongs to the group of about carbenium running surroundings as well as the Wagner -Meerwein rearrangement. Special resemblance is due to the 1,2- shift of the alkyl group to the pinacol rearrangement.

Reaction mechanism

The reaction mechanism is to be shown by the example of cyclohexanone from 1- Aminomethylcyclopentanol 1 and dilute nitrous acid. To this end, the electrophilic Nitrosylkation 2 is prepared in the first step, which is attacked by the lone pair of the nitrogen in the amino group. After completion of the diazotization there is a diazonium cation 3.

Since aliphatic diazonium salts are not stabilized by resonance and therefore being stable compounds, they tend to decay quickly and split a nitrogen molecule from, creating a stable, primary carbenium ion 4 arises in this case. Followed by a 1,2-shift of the alkyl radical, which leads to a ring expansion and the creation of a resonance stabilized carbenium ion 5. Subsequent deprotonation results in cyclohexanone (6).

Application

The reaction can be used to cyclic ketones to expand a methyl group. For this purpose, attached to the carbonyl group of the ketone 1 as nitromethane or cyanide and hydrogenating the corresponding reaction products ( nitromethyl alcohol 2 and cyanohydrin 3) for β -amino alcohol 4.

The rearrangement of β - amino alcohol by Tiffeneau Demianov reaction then yields the ring-expanded ketone 5