Chemically Triggered C–ON Bond Homolysis of Alkoxyamines. Quaternization of the Alkyl Fragment

Abstract

The C-ON bond homolysis in alkoxyamine 2a can be chemically triggered by the protonation of the 4-pyridylalkyl fragment. The resulting 15-fold increase in k(d) (Chem. Commun. 2011, 47, 4291-4293) was investigated experimentally and theoretically by quaternization of the pyridyl moiety using methylating (MeOTs), acylating (AcCl), and benzylating (PhCH(2)Br) agents as well as by oxidation of the pyridyl moiety into N-oxide and by the formation of a dative bond with BH(3) as a Lewis acid.

Chemically triggered C–ON bond homolysis in alkoxyamines. Part 7. Remote polar effect

“…The plots from Eqn 1 (not shown) were as good as those already reported, and k d values are gathered in Table . To facilitate the discussion, all k d values were re‐estimated at 35 °C using Eqn and were noted k d ′.…”

“…Consequently, easy handling of alkoxyamines and efficient initiation of NMP require antagonist kinetic properties of alkoxyamines. To circumvent this issue, we, recently, proposed a new generation of alkoxyamines for NMP, whose main feature was their chemical activation by protonation, oxidation, complexation and alkylation, among which the benzylation as exemplified with 1 and 2a . The activation of 1 by benzylation gave us the opportunity to investigate the remote effect – 10 bonds between the X group and the cleaved C–ON bond – of the polarity of group X at the para position of the benzyl fragment of 2a , 2b , 2c , 2d , 2e , 2f , 2g (Fig.…”

“…Alkoxyamine 1 was prepared as previously reported and alkoxyamines 2a , 2b , 2c , 2d , 2e , 2f , 2g were prepared using an adapted procedure (see SI) based on the quaternization of 1 with the corresponding para ‐X‐benzyl bromide. For 2f , the quaternization was performed using the hydrobromine salt of para ‐dimethylaminobenzyl bromide (see SI) .…”

Chemically Triggered C–ON Bond Homolysis of Alkoxyamines. 5. Cybotactic Effect

“…Chem. XXXX, XXX, XXX−XXX D ■ EXPERIMENTAL SECTION Alkoxyamine 2 was prepared as previously reported 5,7. k d values were measured in 15 solvents using 31 P NMR with TEMPO as alkyl radical scavenger (2 equiv with respect to alkoxyamine) using the reported procedure as exemplified in Scheme 2.…”

Mass spectrometry of nitroxide-terminated poly(4-vinylpyridine): A case of unwanted reactive MALDI

“…Moreover, determination of homolysis rate constants (k d ) in solid state and in a matrix environment is still challenging due to occurrence of many side-reactions. Nevertheless, in solution, activation of the C ON bond homolysis upon protonation or solvation with hydrogen bond donating solvents has recently been reported using 4-VP-SG1 alkoxyamine as a model, respectively showing a 10-fold [27,28] and 3-4-fold [29] increase in k d . Thus, the easy cleavage of the C ON bond in MAMA-P4VP-SG1 would play the role of the driving force as it readily affords a benzylic type radical (event 2), triggering concomitantly the generation of phenoxyl type radical (event 4).…”