References and Notes
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7c
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8
General Procedure
for the Synthesis of N
-Alkoxyamines
Prostab 5198TM (2.50
g, 14.5 mmol) was dissolved in 4-heptanone (18.5 mL, 132.2 mmol),
and 30% aq H2O2 (10 mL, 97.1 mmol)
was added dropwise. Upon cooling to 10 ˚C, CuCl
(100 mg, 7 mol%) was added. The reaction mixture was stirred
overnight at r.t. to give a greenish solution. A peroxide test conducted
at this stage indicated no residual H2O2.
EtOAc (80 mL) was added and the two phases were separated. The organic
phase was washed successively with 10% ascorbic acid soln,
H2O, 10% Na2CO3 soln,
and brine. After drying over sodium sulfate and removal of the solvent,
a green-brown oil was obtained. The product was purified by column
chromatography on SiO2 (hexane-EtOAc, 15:1)
to afford 1.75 g (60%) of 1-propoxy-2,2,6,6-tetramethylpiperidin-4-ol;
off-white solid. ¹H NMR (400 MHz, CDCl3): d = 3.95
(dddd, J = 14.4, 10.4, 3.6,
3.2 Hz, 1 H), 3.70 (q, J = 9.2
Hz, 2 H), 1.80 (dd, J = 14.4, 3.2
Hz, 2 H), 1.70 (br s, 1 H, OH), 1.53 (m, 2 H), 1.46 (dd, J = 10.4,
3.6 Hz, 2 H), 1.24 (2 s, 6 H), 1.15 (2 s, 6 H), 0.95 (t, J = 10.0 Hz, 3 H). ¹³C
NMR (100 MHz, CDCl3): d = 78.4 (s), 63.3 (t),
60.0 (2 q), 48.3 (2 s), 33.2 (2 p), 21.9 (s), 21.0 (2 p), 10.9 (p).
IR (neat): 3279, 2969, 2933, 2877, 1478, 1470, 1371, 1357, 1256,
1194, 1066, 1044, 984, 950 cm-¹. MS: m/z = 216 [M - H]+.
9 Commercial Product of Ciba Inc.
10 TEMPO works equally well. This method
should also be applicable to other nitroxyl radicals.
11a
Rieche A.
Ber. Dtsch. Chem. Ges. B
1931,
64:
2328
11b See also: Kirillov AI.
Zh. Org. Khim. (Engl. Transl.)
1966,
2:
1048 ; and references cited therein
12
Dussault P.
Reactions of Hydroperoxides and Peroxides,
In Active Oxygen in Chemistry
Vol.
2:
Search Series, Chapman and Hall;
London:
1995.
p.150
13
General Procedure
for the Synthesis of N
-Alkoxyamines Using Solvents
Prostab
5198TM (8.6 g, 49.9 mmol) was added to toluene (100 mL),
followed by 1-methoxyacetone (11.0 g, 2.5 equiv) and CuCl (125 mg,
2.5 mol%). The mixture was stirred well while adding 30% aq
H2O2 (17.8 mL, 3.5 equiv) over a period of
1 h. The reaction mixture was stirred at r.t. overnight. Workup:
as reported in ref. 8. Yield 8.89 g (82%) of 1-methoxymethyl-2,2,6,6-tetramethylpiperidin-4-ol,
off-white solid; NOCH2OMe/NOMe ratio = ca.
13.5:1. ¹H NMR (300 MHz, CDCl3): d = 4.01
(m, 1 H), 3.82 (s, 3 H), 1.89 (dd, J = 14.2,
3.6 Hz, 2 H), 1.82 (br s, 1 H), 1.67 (dd, J = 11.0,
3.6 Hz, 2 H), 1.21 (2 s, 6 H), 1.15 (2 s, 6 H). ¹³C
NMR (75 MHz, CDCl3): d = 103.1 (s), 63.5 (2q),
60.1 (t), 56.9 (p), 48.6 (2s), 33.7 (2 p), 21.5 (2 p). IR (neat):
3239, 3005, 2972, 2933, 1467, 1363, 1343, 1245, 1148, 1070, 1003, 929
cm-¹. MS:
m/z = 218 [M - H]+.
14
Syrkin YK.
Moiseev II.
Russ. Chem. Rev.
1960,
29:
193
15
General Procedure
for the Synthesis of N
-Alkoxyamines under Acidic Conditions
Prostab
5198TM (25.1 g, 145.1 mmol) was dissolved in 2-butanone
(105 mL), and 30% aq H2O2 (50.0 mL,
485.3 mmol, ca. 3 equiv) was added over 10 min. Upon cooling to 5 ˚C,
CuCl (0.71 g, 7.2 mmol, 5 mol%) was added and the temperature
was kept between 10 ˚C and 15 ˚C. After
15-30 min, the pH of the reaction mixture was slowly adjusted
to ca. 3.2 using 1 N HCl. The brownish solution was stirred overnight
at r.t. while keeping the pH value at around 3.5 using a dosimat.
A green homogeneous solution was obtained after 12 h. Workup: as
reported in ref. 8. Yield: 22.9 g (114 mmol, 78%) of 1-ethoxy-2,2,6,6-tetramethyl-piperidin-4-ol,
solid, NOEt/NOMe ratio = ca. 9:1. ¹H
NMR (400 MHz, CDCl3): d = 3.93 (dddd, J = 14.4, 11.6, 5.6, 3.6 Hz,
1 H), 3.77 (q, J = 9.6 Hz, 2
H), 1.81 (dd, J = 14.4, 5.6 Hz,
2 H), 1.45 (dd, J = 11.6, 3.6
Hz, 2 H), 1.22 (2 s, 6 H), 1.18 (2 s, 6 H), 1.10 (t, J = 9.2 Hz, 3 H). ¹³C
NMR (100 MHz, CDCl3): d = 72.3 (s), 63.3 (t),
59.8 (2 q), 48.2 (2 s), 33.1 (2 p), 21.0 (2 p), 13.6 (p). MS: m/z = 202 [M - H]+.
16
Stepanow FN.
Smirnow OK.
Zh. Obshch. Khim.
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1957,
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Molawi K.
Schulte T.
Siegenthaler KO.
Wetter C.
Studer A.
Chem. Eur. J.
2005,
11:
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17b
Teichert A.
Jantos K.
Harms K.
Studer A.
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17c
Ahn K.-H.
Kim Y.
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17d
Braslau R.
Burrill LCII.
Siano M.
Naik N.
Howden RK.
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17e
Matyjaszewski K.
Woodworth BE.
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