Thermolysis of a Tertiary Alkoxyamine. Recombination and Disproportionation of α-Phenethyl/Diethyl Nitroxyl Radical Pairs

Abstract

Alkoxyamine 3 undergoes thermolysis only on heating to over 150°C, ∆H q ) 34.3 ( 1.6 kcal/mol and ∆S q ) 0.8 ( 3.7 eu. The initially formed nitroxyl (6) and R-phenethyl radicals (5) mainly disproportionate to styrene plus diethylhydroxylamine (2) but they also recombine to starting material and undergo a new reaction, disproportionation to ethylbenzene plus nitrone (12). The latter reacts with the styrene product to yield oxazolidines 8 and 9. The competition between attack of 5, generated from azo-R-phenylethane (1), on 2 versus styrene allowed us to calculate a rate constant at 120°C of 5 × 10 3 M -1 s -1 for H • transfer from diethylhydroxylamine to 5.

Selective formation of diblock copolymers using radical trap‐assisted atom transfer radical coupling

“…We recently demonstrated that RTA‐ATRC reactions, using the nitrone N ‐ tert ‐butyl‐α‐phenylnitrone (NtBPN) as the radical trap, can be adjusted to give PSt dimers containing mid‐chain alkoxyamine functionality nearly quantitatively . The incorporation of the alkoxyamine unit at the chain's mid point can be visualized by thermal cleavage of the CO bond, regenerating PSt segments approximately the size of the original PStBr precursors . This work was extend in our lab to produce cyclic PSt using an intramolecular RTA‐ATRC sequence, with 2‐methyl‐2‐nitrosopropane (MNP) serving as the radical trap in this case .…”

“…19 The incorporation of the alkoxyamine unit at the chain's mid point can be visualized by thermal cleavage of the CAO bond, regenerating PSt segments approximately the size of the original PStBr precursors. 19,20,22 This work was extend in our lab to produce cyclic PSt using an intramolecular RTA-ATRC sequence, with 2-methyl-2-nitrosopropane (MNP) serving as the radical trap in this case. 23 Thermal cleavage of the CAO bond within the alkoxyamine unit contained in the cycle reverted the product back to a linear polymer chain, clearly evidenced by shifts in the elution volume on gel permeation chromatography.…”

(R)-1,1′-Binaphthalene-2,2′-diol–(Z)-N-ethylideneethanamineN-oxide (1/1)

“…For applications of 2,2 0 -dihydroxy-1,1 0 -dinaphthalene in asymmetric synthesis, see: Noyori et al (1984); Reeder et al (1994); Toda et al (1989); Zhang & Schuster (1994). For related literature on oxidation of hydroxylamines to nitrones, see: Cicchi et al (2001); Engel et al (1997); Liu et al (2004). Table 1 Hydrogen-bond geometry (Å , ).…”

“…Comment 2,2′-Dihydroxy-1,1′-dinaphthalene (binaphthol) is an important chemical as a precursor for catalysis in asymmetric synthesis, as a chiral host for molecular recognition and enantiomer separation and also as intermediates for the synthesis of chiral materials (Noyori et al, 1984;Toda et al, 1989;Reeder et al, 1994;Zhang & Schuster, 1994). N,N-diethylhydroxylamine is easily oxidized to form E and Z type of N-ethylideneethanamine N-oxide (ELDEA) (Engel et al, 1997;Liu et al, 2004;Cicchi et al, 2001). In this study, only the Z type of ELDEA is trapped by the (R)-binaphthol to form the title complex, (I) (Scheme 1 and Fig.…”

The electrochemical reduction of 1,4-dichloroazoethanes: Reductive elimination of chloride to form aryl azines

“…The azo (N N) bond is a relatively labile group often accompanied by the loss of N 2 under a variety of thermal and photochemical conditions [1][2][3][4][5][6][7]. The fragmentation of the C-N bond is rationalized to occur by homolytic cleavage upon photolysis via a radical pathway [4][5][6][7][8].…”