Generation of Iminyl Radicals through Sulfanyl Radical Addition to Vinyl Azides

Abstract

Benzenethiol and 2-benzo[b]thiophenethiol undergo almost instantaneous reaction with α-azidostyrene and 1-azido-trans-stilbene in benzene, at room temperature, to give corresponding β-sulfanylated imines and enamines in virtually quantitative yield. With α-azidostyrene, phenethyl and allyl mercaptan are found to react in a similar fashion, but to rates very much lower. Results are interpreted in terms of radical-chain reactions involving intermediacy of 2-sulfanyliminyl radicals which could result from sulfanyl radical attack at the azide β-carbon followed by nitrogen extrusion by the ensuing radical adduct.

Intermolecular Radical Additions to Alkynes: Cascade‐Type Radical Cyclizations

“…Therefore, S radicals ultimately can promote cyclization of enynes through a mechanism consisting of radical addition to the C:C triple bond, followed by cyclization to the alkene moiety. 58 A similar behavior is also observed in the reactions of other electrophilic heteroatom-centered radicals with enynes (see below). A highly complex radical addition/cyclization/rearrangement reaction is shown in Scheme 2.26.…”

Expeditious diastereoselective synthesis of elaborated ketones via remote Csp3–H functionalization

“…The alkyl radical intermediate undergoes addition onto the vinyl azide present in the reaction media to produce benzylic radical III (TS II–III , Δ G ‡ =12.2 kcal mol −1 ). Release of N 2 is again highly favoured and results in the formation of imine radical IV (TS III–IV , Δ G ‡ <5 kcal mol −1 )34353637. Although a single-electron recombination of IV with the metal centre could be envisioned, the reaction outcome suggests that a 1,5-H migration on the secondary aliphatic C–H bonds to produce a C-centred radical V is preferred2526.…”

“…We hypothesized that aliphatic carboxylic acids could be collected as 1,2-diradical synthons in the presence of vinyl azides34353637, through a radical-mediated decarboxylation process3839. Notably, the reaction involves a regioselective, directing-group free activation of an unactivated aliphatic C–H bond via radical-mediated 1,5-hydrogen transfer and a C sp 2 –H functionalization relay via Minisci-type reaction40, a combination of steps thus far not reported in the literature (Fig.…”

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

“…The radical chain reaction of benzenethiol with a-azidostyrenes had been found to afford virtually quantitative yields of sulfanylated imines and tautomeric enamines, presumably formed from transient iminyl radicals arising from a-azidobenzyl radical adducts by b-elimination of dinitrogen (Scheme 13). [27] Surprisingly, that promising chemical information was totally ignored for over ten years, until a study of the radical reactions of certain azido iodoanilides allowed us to first prove that aliphatic azides might actually behave as excellent sources of iminyl radicals, which are crucial intermediates in the radical synthesis of various cyclic/acyclic nitrogen compounds. [28] This novel approach to iminyl radicals from aliphatic azides was essentially suggested by the known propensity of aryl radicals to rearrange to more stable alkyl radicals through intramolecular 1,5-hydrogen transfer reaction.…”