Novel Heteroatom-Linked Analogues of Trityl Radicals:  Diaryl(benzotriazol-1-yl)methyl Radical Dimers

Abstract

The lithiation of diaryl(benzotriazol-1-yl)methanes followed by addition of iodine generates phenanthridines and dimers of hitherto unknown trityl analogues in which the radical center is directly attached to a heteroatom. These dimers differ from those of triarylmethyl radicals by not dissociating in solution, but variable temperature ESR measurements provided direct evidence for the formation of the corresponding diaryl(benzotriazol-1-yl)methyl radicals as intermediates in solution.

1,2,3-Triazoles

“…One of the possible reactions of radicals 208 is ring opening to give radicals 209 . Elimination of nitrogen from 209 produces unstable species 210 that undergo intramolecular cyclization to phenanthridines 211 ( Scheme 25 ) 1996JHC607 , 1998JOC1467 . When substituents X and Y are identical, products 211 are obtained with average yield of 50%.…”

“…Polycyclic phenanthridines are formed in these reactions when tricyclic analogs of 206 derived from acridine, xanthene, or thioxanthene are used as starting materials <1999JHC927> . Another possible reaction of radicals 208 is their dimerization resulting from combining one radical with another in position para of the aromatic ring (when X = H) <1998JOC1467> .

Scheme 25

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“…Acidic hydrolysis converts adduct 449 into carbinol 451 . Radicals similar to 448 can be also generated from 1-(diarylmethyl)benzotriazoles, but they are less stable undergoing easily ring opening with extrusion of nitrogen <1998JOC1467> .

Scheme 73

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A facile access to indigodianiles

“…Spectra of different derivatives of type 6 are nearly identical. Most likely the radicals formed in both reaction pathways derive from benzotriazole derivatives [18]. Taking these findings into account, the following mechanism is proposed for the reaction with metallic lithium.…”

A Benzoquinone Imine Assisted Ring‐Opening/Ring‐Closing Strategy of the RCOCHN1N2 System: Dinitrogen Extrusion Reaction to Benzimidazoles

“…In the past, the Katritzky group produced several important heterocycles by using benzotriazoles as synthetic auxiliaries . Benzotriazoles (BTZs), owing to their diverse roles in chemical transformations and in the discovery of bioactive scaffolds, have proven to be intriguing substrates . However, owing to their innate tendency to exist as diazonium salts and to their high structural stability, the ring‐opening chemistry of benzotriazoles has not been well studied .…”