Chemistry of amidyl radicals: intramolecular reactivities of alkenyl amidyl radicals

Abstract

Amidyl radicals possessing Δ4,5, Δ5,6, and Δ6,7 double bonds were generated from the photodecomposition of nitrosamides and chloramides and the products were identified. Dichotomies of amidyl radical reactivities were discovered and compared with published kinetic rate constants. In complete reversal to intermolecular reactivities, intramolecularly the alkenyl amidyl radicals preferentially add to the double bonds rather than abstract a C-5 hydrogen even if it is allylic. In intramolecular competition, amidyl radicals add to an acyl side chain double bond more efficiently than to an alkyl one; this is just the opposite to intramolecular H-abstraction of amidyl radicals. Taken together with the published results, it is established that, in intramolecular attacks of double bonds, amidyl radicals selectively undergo the propia-addition to generate an exo-cyclic radical rather than the longa-addition to an endo-cyclic radical: this rule should replace the old one that amidyl radicals preferentially cyclize to form five-membered rings if choices are available.

Recent progress in the generation and use of nitrogen-centred radicals

“…One early approach, which has since been very seldom employed, consists in the photolysis with UV light of N-nitrosoamides. 7 More recently, El Kaim and Meyer discovered that imines derived from N-aminobenzotriazole were convenient precursors for iminyls through the action of stannyl radicals, generated in the usual manner from tributytin hydride. 8 The synthesis of pyrroline 10 from N-benzotriazolylimine 9, which need not be isolated, is typical.…”

Versatile New Reagent for Nitrosation under Mild Conditions

“…We sought to explore alternative sources of N-centered radicals for C–H abstraction, and became interested in nitrosoamines and nitrosoamides as potential radical precursors. A large body of work by Chow involves the generation of N-centered radicals via the light-mediated cleavage of N–NO bonds . Several N-centered radicals derived from simple cyclic nitrosoamides were capable of C–H abstraction in our hands but with limited synthetic efficiency.…”

Stereoselective Cyclization Reactions of IBX-Generated Alkoxyamidyl Radicals

“…On the basis of these results, it is obvious that the more electrophilic amidyl radicals cyclize faster than aminyl radicals . Amidyl radical cyclizations have been studied using N -chloroamides, N -phenylthioamides, N -hydroxypyridine-2( 1H )thione derivatives, N -nitrosoamides, and other systems 8 as radical precursors. Herein we present our first results on cyclization reactions of alkoxy-substituted amidyl radicals (eq 1) .…”