Nucleophilic aromatic substitution rearrangements

Rearrangement by nucleophilic aromatic substitution and aromatic mgrallon trom one hetero atom to another (O lo N or S lo O)... 

When aromatic nitro compounds are treated with cyanide ion, the nitro group is displaced and a carboxyl group enters with cine substitution (p. 854), always ortho to the displaced group, never meta or para. The scope of this reaction, called the von Richter rearrangement, is variable. As with other nucleophilic aromatic substitutions, the reaction gives best results when electron-withdrawing groups are in ortho and para positions, but yields are low, usually < 20% and never > 50%. 

Excited-state intramolecular nucleophilic aromatic substitutions are known as photo-Smiles rearrangements. Ealier, these were reported for 2,4-dinitrophenyl ethers and. v-lriazinyl ethers32. The exploratory33 and mechanistic34 studies on photo-Smiles rearrangements of p-(nitrophenoxy)- >-anilinoalkanes were carried out (equation 28). 

Miscellaneous PTC Reactions The field of PTC is constantly expanding toward the discovery of new enantioselective transformations. Indeed, more recent applications have demonstrated the capacity of chiral quaternary ammonium salts to catalyze a number of transformations, including the Neber rearrangement (Scheme 11.19a), ° the trifluoromethylation of carbonyl compounds (Scheme 11.19b), ° the Mannich reaction (Scheme 11.19c), and the nucleophilic aromatic substitution (SnAt)... 

Monoalkylation of a-isocyano esters by using tert-butyl isocyano acetate (R = fBu) has been reported by Schollkopf [28, 33]. Besides successful examples using primary halides, 2-iodopropane has been reported to produce the a-alkylated product (1) as well by this method (KOfBu in THF). In the years 1987-1991, Ito reported several methods for the monoalkylation of isocyano esters, including the Michael reaction under TBAF catalysis as described earlier [31], Claisen rearrangements [34], and asymmetric Pd-catalyzed allylation [35]. Finally, Zhu recently reported the first example of the introduction of an aromatic substituent by means of a nucleophilic aromatic substitution (Cs0H-H20, MeCN, 0°C) in the synthesis of methyl ot-isocyano p-nitrophenylacetate [36]. 

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