Iminyl Radicals from α-Azido o-Iodoanilides via 1,5-H Transfer Reactions of Aryl Radicals: New Transformation of α-Azido Acids to Decarboxylated Nitriles

Abstract

The radical reaction of tributyltin hydride with o-iodo- N-methylanilides derived from alpha-azido acids provides an excellent access to alpha-(aminocarbonyl)iminyl radicals through 1,5-hydrogen transfer reaction of initially formed aryl radicals followed by beta-elimination of dinitrogen from ensuing alpha-azido-alpha-(aminocarbonyl)alkyl radicals. The outcoming iminyls display a peculiar tendency to form corresponding nitriles by beta-elimination of aminocarbonyl radicals.

A new era for homolytic aromatic substitution: replacing Bu3SnH with efficient light-induced chain reactions

“…There are examples of iminyl radicals undergoing HAS, 20 including cascades from N-acyl cyanamides with aromatic substitution facilitated by virtue of displacement of a substituent (hydrogen or alkyl) on the aromatic ring. [21][22][23] Although HAS is part of the cascade due to the migration of the hydrogen atom an overall reduction occurs (Scheme 5).…”

Visible Light‐Induced Radical Cyclization of Ethyl 2‐(N‐Arylcarbamoyl)‐2‐Chloroiminoacetates: Synthesis of Quinoxalin‐2(1H)‐ones

“…[5,6] Recents tudies by Spagnolo et al, [7] Zhang et al [8] and us [9] demonstrate that the cyclization of a-(aminocarbonyl)iminyl Scheme1.Photo-induced iminyl radicalc yclization via N À X bond cleavage. radicalsw ouldp rovide as imple approach towards quinoxalin-2(1H)-one derivatives.T his approach is advantageous comparedw ith the commonly used methodsi nt hat it employs simple anilinesi nstead of 1,2-disubsituted aniline derivatives as precursors.D espite the synthetic usefulness of this method,however, the reported proceduress uffer from competition from other pathways, [7][8][9][10] and therefore,i ti sh ighly desirable to develop new protocols to overcome this obstacle.…”

From Azides to Nitrogen‐Centered Radicals: Applications of Azide Radical Chemistry to Organic Synthesis

“…Indeed, for curious reasons, in such cases the initial aryl radicals are much more prone to give sixmembered ipso-cyclization onto the adjacent aromatic ring instead of bringing about the normal 1,5-H transfer reaction. [29] Even more interestingly, in a subsequent work we established that also aromatic azides are possible precursors of iminyl radicals whenever homolytic ipso-attack can take place at the para (and, presumably, the ortho) position of the azido-substituted benzene ring. [30] Indeed, it was found that the radical reaction of accessible 2-iodo-p-azidobenzanilides 27 with (TMS) 3 SiH and Et 3 B/air in benzene or toluene at ambient temperature gave rise to precipitation of large amounts of indolone imine hydroiodides 32, isolable by direct filtration of the reaction mixture (Scheme 15a).…”

“…The high efficiency of such tandem hydrogen translocation/dinitrogen extrusion process was further substantiated by the general failure to observe any deiodinated product, which might have resulted from tin hydride reduction of both/either aryl radical 20 and/or the translocated azidoalkyl radical 21. [29] In refluxing benzene, the resulting a-alkyl-substituted iminyl radicals 22 usually underwent highly selective b-fragmentation yielding carbamoyl radicals 23, and thence formanilide 25, along with the corresponding alkanenitrile 24.…”

“…Under these thermal conditions, iminyls 22 could also undergo aromatic cyclization to oxoquinoxaline 26, but to a very limited extent (Scheme 14b). [29] Using more forcing thermal conditions (refluxing toluene), fragmentation of iminyl 22 to nitrile 24 was further improved, thus allowing a valuable protocol for the unprecedented conversion of easily accessible a-azido acid to decarboxylated alkanenitrile via the anilide derivative 19. This protocol is, however, not very useful for achieving aromatic nitriles from anilides 19 bearing an aryl instead of an alkyl on the a-carbon.…”