New Method for the Synthesis of N-tert-Alkoxyarylaminyl Radicals¹

Abstract

The reactions of 2,4-diaryl-6-tert-butylnitrosobenzenes with 2,2'-azobis[2-(methoxycarbonyl)propane] (5a), 2,2'-azobis(2-cyano-4-methylpentane) (5b), and 2,2'-azobis(2-cyano-4-methyl-4-methoxypentane) (5c) in refluxing benzene gave stable N-tert-alkoxy-2,4-diaryl-6-tert-butylphenylaminyls, which were successfully isolated as radical crystals in 13-52% yields after column chromatography. The radical yields depended on the reaction time and the molar ratio of azo compounds to nitroso compounds. In the same manner, acetyl- and cyano-group-carrying N-tert-alkoxyarylaminyls were generated by the reaction of 2-phenyl-4-(4-acetylphenyl)-6-tert-butylnitrosobenzene and 2-phenyl-4-(4-cyanophenyl)-6-tert-butylnitrosobenzene with 5a and 5b, and they were isolated as radical crystals. X-ray crystallographic analyses were performed for two radicals, and their molecular structures were discussed in detail. The magnetic properties were measured for the two isolated radicals with SQUID in the temperature range 1.8-300 K. One radical showed a weak ferromagnetic interaction (theta = 0.2 K) between the radicals, and the other showed a weak antiferromagnetic interaction (theta = -3.8 K). The ferromagnetic interaction was analyzed based on the X-ray crystallographic structure.

Electrochemical study of stable N-alkoxyarylaminyl radicals

“…These large E p values demonstrate that the reduction from radicals to anions is a slow one-electron transfer process, which can be ascribed to a large geometry change in the reduction from radicals to anions. Previous X-ray crystallographic studies for 1a and 2 showed that the radicals have a planar conjugated -system [12,17]. This indicates that the nitrogen 2p z orbital accommodating a unpaired electron and the oxygen 2p z orbital accommodating the lone pair of electrons are parallel to each other to form a two center-three electron bond between N and O [22].…”

“…High resolution FAB mass spectra (HRFABMS) were recorded with a JEOL JMS-7000T mass spectrometer. (2) and N-tert-butoxy-2,4,6-tris(4-chlorophenyl)phenylaminyl (3) were prepared by our previously reported methods [12,16,17]. N-[(4-Nitrophenyl)thio]-2,4-bis(4-chlorophenyl)-6-tert-butylphenylaminyl (9) was prepared according to our previously reported method [21].…”

“…Although N-alkoxyaminyl radicals were extensively studied by ESR spectroscopy over a long time [1][2][3][4][5][6][7][8][9][10], the first isolation of N-alkoxyaminyls by our group was quite recent [11][12][13][14][15][16][17]. We obtained isolable N-alkoxyarylaminyls by two methods.…”

“…We obtained isolable N-alkoxyarylaminyls by two methods. One method involves the reaction of the lithium salts of 2,4,6-tri-substituted anilines with tert-alkyl peroxybenzoates [11][12][13][14][15] and the other involves the reaction of 2,4-diaryl-6-tert-butylnitrosobenzenes with azo compounds [16,17]. Interestingly, the isolated N-alkoxyarylaminyls are stable in the presence of oxygen even in solution and, although they were heated at 80 • C in benzene for 10 days, 80% of the radical survived.…”

Dirhodium(II)‐Catalyzed Intramolecular CH Amination of Aryl Azides

“…[18a] Whereas this reaction exhibited a broad substrate scope, it required an a-azidomethylacetate, which restricted product formation to 2-indolecarboxylate esters. [17c] Achievement of indole synthesis from aryl azides 3 through rhodium-catalyzed vinyl CÀH bond amination would address this limitation as a broader range of aryl azides are readily available from commercial starting materials in two mild, functional group tolerant steps: palladium-catalyzed Suzuki cross-coupling of 2-bromoanilines [19] and subsequent diazo transfer would produce 3. [20] The combination of this potential method with our earlier one would enable the rhodium-catalyzed synthesis of indoles by the formation of either the aryl C À N bond (from azidoacrylates) or the creation of the vinyl CÀN bond (from aryl azides; Scheme 1).…”