Turpin reaction

Tungsten, tricarbonyleyelopentadienylhydrido-reaction with ynamines, 1, 666 Turpin reaction, 3, 1033 Tylophorine occurrence, 4, 478 synthesis, 4, 472, 475 Tylosin... 

The presence of groups other than nitro (e.g. CH3, OCH3,1) at the position 6 also facilitates the Turpin reaction (30JCS1218, 60JIC647, 65JIC101). In this case, the steric influence of the groups must play an important role. A similar effect was also described for the 5-ethyl group ethyl derivative 180 provided... 

Halonitropyridines also easily react with aminophenols to give the corresponding intermediates, which are suitable for the Turpin reaction. Eqs 20 and 21 show two literature examples of this reaction providing azaphenoxazines 190 and 192, respectively (45JCS313, 58CPB46, 58CPB378). 

Chloro-l-methyl-4-nitroimidazole (204) was also used as a heterocyclic component in the Turpin reaction. Intermediate 205 was formed under mild conditions and its cyclization was achieved by heating with ethanolic dimethylamine in a sealed tube to give a blue-colored substance, which was attributed structure 206 (Scheme 32) (52JCS784). 

These and other venerable synthetic routes to the tricyclic oxazines and thiazines have been reviewed in detail (B-78MI22701). 2-Hydroxy(or mercapto)-2, 4 -dinitrodiphenylamines readily cyclize to phenoxazines (or phenothiazines) in basic media through elimination of nitrous acid. This is the so-called Turpin reaction, which is complicated by the fact that the intermediate Meisenheimer complexes (251) may undergo a Smiles-type rearrangement so that mixtures of isomeric products are obtained (Scheme 112). 

Phenoxazine itself reacts very violently even with dilute nitric acid to give tetranitrophenoxazine (25, X = N02) and no mono or dinitro derivatives.64 V-Acetylphenoxazine, however, is nitrated in acetic acid to give a mononitro-A-acetylphenoxazine,26 which after deacetylation proved to be identical with 3-nitrophenoxazine (23, X = N02), obtained by the Turpin reaction (see Section II, A, 2). On nitration in acetic anhydride A-acetylphenoxazine yielded a mixture of 25 (X = N02) and the acetyl derivative of 24 (X = N02). 

Abbasi, M., Nasr, M., Zoorob, H. H., and Michael, J. M., Reactivity of 4-hydroxy-2-mcthyl-7,8,9,l0-tctrahydrobcnzo h)quino-line towards base-catalyzed cyclization, Mannich and Turpin reactions, J. Heierocycl. Chem.. 15,649, 1978. 

Sodium hydroxide Phenoxazine ring—Turpin reaction... 

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