Homolytic Cyclizations of N‐Chloroalkenylamines

Abstract

Dedicated to Professor Jean-Marie Surzur on the occasion of his 50th birthdayMany N-chloroalkylamines with double bond(s) dissociate homolytically to give chlorine atoms and aminyl radicals which undergo intramolecular cyclization reactions. Here, the nature of the aminyl radicals (neutral, protonated, or complexed to metal salts) appears to be important. The reactivity varies strongly from one species to another, and their selectivities can be different towards addition, substitution, abstraction, or dimerization reactions. A good synthetic tool appears to be the "complexed radical", which is generated under mild conditions. A variety of 0-functionalized, substituted, fused, or bridged azaheterocycles with alkaloid part structures thus become easily accessible in high yields, in a regio-and, possibly, stereoselective manner. Many examples are discussed illustrating the synthetic possibilities, limitations, and mechanistic features of this cyclization process.

Radical ion cyclizations

“…In the absence of thiol, the carbon-centered radical reacts with the PTOC precursor to yield the 2-pyridyl alkyl sulfide 130, the so-called selftrapped product. Cyclization of analogous N-chloramines and nitrosamines to pyrrolidines and piperidines, conducted under either strongly acidic or under mild acidic conditions, have been investigated earlier by Surzur and Stella [142][143][144][145].…”

Stable Reagents for the Generation of N‐Centered Radicals: Hydroamination of Norbornene

“…In contrast to well-established procedures using N-halogen derivatives as N-radical precursors, [2] an additional stoichiometric reducing reagent such as the toxic tributyltin hydride is not necessary for N-radical generation. Moreover, the radical precursors are readily prepared and are stable compounds.…”

“…[4] N radicals are generally generated via N-halogen, N-PTOC (PTOC = N-hydroxypyridine-2(1H)thione) and Nphenylthio derivatives either photochemically or by using an added reducing reagent. [2] However, most of these precursors are unstable and must be prepared in situ. Herein we present new stable N-radical precursors.…”

“…However, radical additions of amines or amine derivatives to olefins by H-transfer processes are not known to date. Whereas the addition of N radicals to alkenes is well established, [2,3] the H transfer from N to C radicals is not an efficient process [Eq. (1)].…”

Carboamination of Unactivated Alkenes through Three‐Component Radical Conjugate Addition

“…[11] However,t hree-component radical additions of unactivated alkenes to Michael acceptors where the C-radicals are generated by intermolecular C À Xb ond formation leading to alkene 1,2-difunctionalization products have not been reported. [14] Carboamination of activated alkenes including styrenes and acrylates has gained attention recently, [15] but the herein disclosed strategy shoutable for unactivated alkenes has not been established to date. [14] Carboamination of activated alkenes including styrenes and acrylates has gained attention recently, [15] but the herein disclosed strategy shoutable for unactivated alkenes has not been established to date.…”