Fixation of NOX Gases
FULL PAPER
spectral data for amides 5a–s were published in the supplementary mate-
was evaporated and the residue was analyzed by 1H NMR spectroscopy
in CDCl3.
rials in associated with reference [5] and elsewhere.[33–44,7h]
(R,S)-N-Methyl-(2-methyl)valeramide ((R,S)-5t): Yield=50%; 1H NMR
([D6]benzene): d=5.6 (brs, 1H), 2.42 (d, J=4.5 Hz, 3H), 1.96 (m, 1H),
1.82 (dd, J=14.5 Hz, J=6.0 Hz, 1H), 1.55 (dd, J=14.5 Hz, J=6.0 Hz,
1H), 1.3 (m, 1H), 1.1 (m, 1H), 0.87 (d, J=7.0 Hz, 3H), 0.82 ppm (t, J=
7.5 Hz, 3H); 13C NMR: d=173.8, 44.0, 32.3, 29.5, 26.2, 19.2, 11.4 ppm;
EI-MS: m/z calcd for C7H17NO: 129.1; found: 129.0 [M+].
Acknowledgements
Financial support is acknowledged from the Texas Advanced Technology
Program (003656-0146-2003), NSF (CHE-0350958) and the Alfred P.
Sloan Foundation.
(S)-3-Methylpentyl N-methyl amide ((S)-5t): The mixture of (S)-3-Meth-
ylpentanoic acid[45] (2 mL) and SOCl2 (15 mL) was refluxed for 4 h.
Excess SOCl2 was evaporated in vacuum and the resulting acid chloride
was redissolved in CH2CL2 (10 mL). This solution was added dropwise to
the mixture of methylamine and Et3N in CH2CL2 (10 mL) at ~08C. The
resulting mixture was stirred at RT for 2 h, and then acidified with 10%
aq HCl, washed with water (3ꢃ15 mL), dried over MgSO4, and evaporat-
ed under reduced pressure. Yield 90%.
dex.html.
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General nitrosation procedure with encapsulated reagents: Calixarene–
nitrosonium complex 2 (1 equiv) was added to the solution of amide 5
(~5 equiv) in freshly distilled CH2Cl2 or CHCl3, and the reaction mixture
was stirred at RT for 2–3 h until bleaching. The solvent was evaporated,
and the residue was analyzed by 1H NMR spectroscopy and in some
cases separated by preparative TLC, resulting in N-nitrosoamides as
orange oils. All runs were performed at least in duplicate. The spectral
data for the obtained N-nitroso compounds 6a–e,t were identical with
those independently obtained from 5a–e,t and NO2/N2O4 in CHCl3 (>
95% yields) following the literature protocols.[46] N-nitrosamides 6 f–s
cannot be obtained from 5 f–s and complexes 2. These were prepared, for
spectral comparison, by employing NO2/N2O4 in CHCl3. The spectral
data for nitrosamides 6a–s were published in the supplementary materi-
als associated with reference [5] and elsewhere.[47–52,7h,26b]
Nitrosation with chiral reagents (2c,d): The standard nitrosation proce-
dure was applied, after which the reaction mixture was evaporated under
reduced pressure at RT. The residual oil was separated by column chro-
matography with hexanes/CH2Cl2 (2:1) for 2c+5t and hexanes/C6H6
(3:1) for 2d+5t. Fractions containing N-nitroso-(2-methyl)valeramides
6t were collected and evaporated under reduced pressure at RT. The re-
sulting oil was treated with TFA (20–25 mL) at RT for 14 h, after which
the volatiles were evaporated to give pure N-methyl-(2-methyl)valer-
amides 5t in 40–50% yield.
For identification purposes, amide 5t was separately prepared in both the
enantiomerically pure (S)-form and as a racemate. The 1H NMR signals
were assigned through COSY experiments. The optimal stoichiometry for
the Pirkle reagent was established, which is ~6 equiv in [D6]benzene.
Particularly useful for the ee determination are the methylene CH2C(O)
signals and, to lesser extent, both methyl CH3 groups of 5t. In the ab-
sence of the shift reagent, the diastereotopic methylene CH2C(O) pro-
tons exhibit two sets of doublets (J=14.5 Hz) at d=1.82 and 1.55 ppm.
Addition of the shift reagent to racemic 5t splits the more downfield set
into three doublets at d=1.55, 1.53 and 1.51 ppm in a 1:2:1 ratio. The in-
tensity of the left and right doublets varies with respect to the enantio-
1
meric ratio. In the H NMR spectrum of amides 5t, obtained after the re-
action with 2c, the diastereotopic methylene CH2C(O) protons exhibited,
in particular, three doublets at d=1.55, 1.53 and 1.51 ppm in exact 1:2:1
ratio. No chiral discrimination was seen. In the 1H NMR spectrum of
amides 5t, obtained after the reaction with 2d, the same CH2C(O) pro-
tons exhibited the three doublets at in a ~0.85:2:1.15 ratio. The intensity
of the right doublet, assigned to the (S)-enantiomer was higher and
showed good reproducibility in at least three independent experiments.
(R,S)-N-Methyl-N-nitroso-(2-methyl)valeramide ((R,S)-6t): 1H NMR: d=
3.16 (m, 1H), 3.10 (s, 3H), 3.0 (m, 1H), 2.07 (m, 1H), 1.43 (m, 1H), 1.30
(m, 1H), 0.98 (d, J=8.0 Hz, 3H), 0.88 ppm (t, J=8.0 Hz, 3H); 13C NMR:
d=177.2, 41.5, 32.1, 29.6, 25.7, 19.8, 11.3 ppm; EI-MS: m/z calcd for
C7H14N2O2: 158.1; found: 158.1 [M+].
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Nitrosation procedure with silia gel supported reagent (4): The suspen-
sion of material 3 in dry CH2Cl2 NO2/N2O4 was bubbled for ~10 s. The
dark-blue colored solid was filtered off and washed with CH2Cl2 and sus-
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