Von richter rearrangement

Von richter rearrangement smile rearrangement

1. Von Richter Rearrangement & Smiles Rearrangement Submitted By :- Dalpat Singh

2. Von Richter Rearrangement :- It is called Hydro-de-nitro-cine-substitution. When aromatic nitro compounds are treated with cyanide ion, the nitro group is displaced and a carboxyl group enters always ortho to the displaced group never meta or para. It is an example of Cine substitution . As with other nucleophilic aromatic substitutions, the reaction gives best results when electron-withdrawing groups are in ortho and para positions

3. Mechanism :- ..

4. N2 is a major product of the reaction. This indicates that nitrogen-nitrogen bond must be formed during the course of the reaction (46) is a stable compound; hence it should be possible to prepare it independently and to subject it to the conditions of the von Richter rearrangement. This was done and the correct products are obtained. When the reaction was performed in H 2 18 O , with CN – , half the oxygen in the product was labelled, showing that one of the oxygen of the carboxyl group came from the nitro group and one from the solvent, as required by this mechanism. When the reaction is carried out in the presence of D 2 O/C 2 H 5 OD, the carboxylic acid formed contains the deuterium at the position originally occupied by the NO 2 group. This confirms the formation of species. Evidences in support of the above mechanism :-

5. Smiles Rearrangement :- The Smiles rearrangement actually comprises a group of rearrangements that follow the pattern given above -

6. Smiles rearrangements are simply intramolecular nucleophilic substitutions. In the example given, SO2Ar is the leaving group and ArO - the nucleophile, and the nitro group serves to activate its ortho position. Here X is usually S, SO, SO 2 , O , or COO, and Y is usually the conjugate base of OH, NH 2 , NHR, or SH. The reaction has even been carried out with YH = CH 3 (phenyl lithium PhLi was the base here ) , in this case this reaction is called truce smiles rearrangement.

7. Z and Z ’ are activating groups for nucleophilic aromatic substitution reaction. Z or Z ‘ should be an electron with drawing group such as –NO 2 , -CN , or CF 3 to stabilize the cyclohexadienylide anion formed. In this rearrangement the chain linking X and Y can be aromatic as well as aliphatic. This rearrangement also takes place in heterocyclic aromatic systems. Examples of substrates which follows smiles rearrangement :-

8. Examples of smile rearrangement :-

9. The presence of an electron with drawing group para to the YH in the substrate retards the rate of the smiles rearrangement because such groups reduce the nucleophilicity of Y -

10. Thank you Submitted to :- Dr. M.R.K. Sherwani