Anthranilium salts

N-Alkylation of anthranils has been achieved using r-butyl alcohol in 60% perchloric acid,233,234 methyl fluorosulfonate,235 dimethyl sulfate,236 triethyloxonium tetrafluoroborate,237 and, unusually, trialkyl orthoformates in the presence of boron trifluoride etherate.237 Rate studies for the N-methylation of anthranils in dimethyl sulfate are available.36 

JV-Alkylanthranilium salts, like their parent anthranils, are readily reduced to 2-alkylaminoacylbenzenes. Sodium dithionite,236,237 zinc,237 or iron in acetic acid,238 and palladium charcoal and hydrogen238,239 are the usual reducing agents. Reduction with sodium borohydride produces the synthetically useful benzisoxazolines (170) in high yield233,237 (see Section III,G,1). 

3-Methylanthranilium salts condense readily with aldehydes, ketones, orthoesters, and diazonium salts to yield styryl, cyanine, and azo dyes, respectively.235 An interesting aspect of these anthranilium salts is their bifunctionality, the 3-methyl group being nucleophilic whereas the C-3 position is electrophilic. As a consequence, base-catalyzed condensation with aldehydes bearing a nucleophilic function at the ortho position (e.g., 

2- hydroxy-l-naphthaldehyde) allow thermochromic spiroisoxazolines, e.g., 174, to be prepared.235 

In view of the results discussed in Section III,C,7, it is not surprising that photolysis of N-alkylanthranilium perchlorates in aqueous solution leads to the formation of 3- and 5-hydroxy-2-alkylaminoacylbenzenes.240 Addition of inorganic ions (e.g., Cl-, Br-, or SCN-) produces the correspondingly 

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The formation of transient benzazetidinones (251) in the photolysis and thermolysis of benzotriazin-4-ones (250) is well established (76AHC215) and the highly hindered adamantyl derivative has actually been isolated from flash pyrolysis of 4-adamantylbenzotriazinone (73JCS(Pl)868). A second route to such hindered benzazetidinones involves cyclization of the iminoketene valence tautomer (252 R = Bu ), the latter being generated by deprotonation of the anthranilium salts (253) (71JA1543). 

By the late 1980s it was clear that a significant number of thermal and photochemical reactions of arylhydroxylamines and their derivatives, N-chloroanilines, aryl azides, anthranilium salts, and other compounds could be explained in terms of nitrenium ions or transition states that resembled nitrenium ions. Since no monoarylnitrenium ion had been directly observed, and data on the lifetimes and quantitative reactivity/selectivity of these species were not available, it was not possible to assess whether the reactions that had been observed were due to free ions, or ion pairs, or preassociation processes. In many cases Sn2 reactions could not be ruled out because appropriate kinetics experiments had not been performed. Most authors had attributed the presence of reduction products in thermal and photochemical reactions to triplet ions, but calculations suggested that the triplet species may not be accessible in thermal processes. It was clear that singlet ions could be reduced under certain conditions, so the presence of the... 

Falvey and co-workers used the N-ferf-butyl-3-methylanthranilium salts 130a-h as photoprecursors to the nitrenium ions 131a-h (Scheme 55). The unsubstituted 130a and related anthranilium salts and anthranils had previously been investigated as photoprecursors for nitrenium ions, but no attempts had been made to directly detect transient ions. Transients identified as 131b-f were detected by UV spectroscopy as products of the... 

N-r-Butylbenzisoxazolines (170 R1 = t-Bu, R2 = H, R3 = Ar), prepared by sodium borohydride reduction of the anthranilium salts (see Section III,D), on heating at 150- 160°C isomerize to o-t-butylaminoacylbenzenes.233 The reaction has merit as a preparative route to o-aminobenzaldehydes, especially as only neutral conditions are employed. 

TABLE 13.5. A-tert-Butyl-A-aryl Nitrenium Ions Generated throngh LFP of Anthranilium Ion Salts"... 

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