Retro-Ritter reaction

Side reactions consistent with decomposition of intermediate nitrilium salt 7 have also been observed, including retro-Ritter reactions that afford alkenes (8), and VonBraun reactions that provide alkyl chlorides (9). ... 

DFT calculations on the Mg(L—H)(L) complex reveal how water and acetonitrile can be lost (Scheme 9). Thus intramolecular proton transfer tautomerizes the neutral acetamide ligand in 48 into the hydroxyrmine form in 49, which can then dissociate via another intramolecular proton transfer to yield the four-coordinate adduct 50, which now contains both water and acetonitrile ligands. It is this complex that is the direct precursor to water and acetonitrile loss. Note that the reaction shown in Scheme 9 is a retro-Ritter reaction and involves fragmentation of the neutral rather than the anionic acetamide ligand, which is a bidentate spectator ligand. 

Retro-Ritter reaction amide into alkene reverse sequence to above SOCI2 or P4O10. Intramolecular Ritter reaction alkene (etc.) into heterocycle sequence (130) -> carbenium ion - (129) - (131) (where Y is a nucleophilic substituent) H2SO4 then H2O. 

Wagner-Meerwein (sec. 12.2.B),i 72,178 and (4) a retro-Ritter reaction.It is noted that the Ritter reaction 0 couples and alkene and a nitrile to give an amide. 

Fragmentation of the nitrilium ion interferes with the cyclization - of 1,2-diphenylethane derivatives, leading to formation of stilbenes rather than cyclization products. This problem has been overcome by using Oxalyl Chloride instead of (1). Fragmentation (von Braun reaction or retro-Ritter reaction) occurs... 

Reformatsky reaction, 1, 1 22, 4 Reimer-Tiemann reaction, 13, 2 28, 1 Reissert reaction, 70, 1 Resolution of alcohols, 2, 9 Retro-Diels-Alder reaction, 52, 1 53, 2 Ritter reaction, 17, 3... 

The mechanism has been further supported by the isolation and characterization of retro-Ritter by-products observed from the Bischler— Napieralski reaction. The retro-Ritter by-products are formed by decomposition of the proposed nitrilium salts. 

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