Sulfonyl- and Carbonylnitrenes
dispersion. Azoxybenzene was used as the actinometer.64 Samples
were placed in a 1 cm square quartz cell mounted on a holder such
that all the light exiting the monochromator hits the sample directly.
Except as noted, initial concentrations were 1-4 mM and the
solutions were bubbled with Ar for at least 10 min to remove O2
prior to photolysis. The progress of reactions was monitored by
HPLC, using a diode array UV/vis detector with a C18 reversed-
phase column for separation. All reported yield data represent at
least duplicate experiments, and most were carried out in triplicate
or greater. Experiments done with octene were either done at an
approximate 10% ((approximately 0.5%, by volume) or at precisely
measured concentrations of alkenes as stated in the text.
for this phenomenon, in which we suggest that most of the
nitrene is formed initially in the triplet state. With sufficiently
slow triplet reactivity with the alkene and modest ∆EST (e10
kcal/mol), one could imagine thermal population of the singlet
nitrene on the µs time scale, which would accommodate the
data easily. However, it does require that little if any singlet
nitrene is formed on direct photolysis, a result that is not
common to the other analogs in this series. That said, the alcohol
trapping results (Table 7), which show no typical singlet O-H
insertion product, regardless of conditions, is also unique to this
compound.
Quantum yields for appearance of dibenzothiophene were
determined using HPLC detection with reactions carried out only
to low conversion. Product yields were determined from reactions
run to nearly complete conversion of starting materials. Identifica-
Experimental Section
Time-Resolved IR Methods. The TRIR experiments have been
conducted following the method of Hamaguchi and co-workers,
as previously described.57–59 In short, the broadband output of a
MoSi2 IR source is crossed with excitation pulses from either a
Q-switched Nd:YAG laser (266 nm, 90 ns, 0.4 mJ) operating at
200 Hz or a Nd:YAG laser (266 nm, 5 ns, 2 mJ) operating at 15
Hz. Changes in IR intensity are monitored using an ac-coupled
mercury/cadmium/tellurium (MCT) photovoltaic IR detector, ampli-
fied, digitized with an oscilloscope, and collected for processing.
The experiment is conducted in dispersive mode with a commercial
spectrometer.
Computational Methods. Vibrational frequencies for the TRIR
experiments were calculated at B3LYP/6-31G(d), using the
GAUSSIAN 9860 suite of programs. All other computations were
carried out using the GAMESS61 suite. The output of the GAMESS
calculations was visualized using MacMolPlt.62 Initial geometries
for the GAMESS runs were obtained from semiempirical or HF
runs done with Spartan.63 Triplet calculations were based on ROHF
wave functions. The coefficients and exponents for the G3Large
g3theory.htm. All stationary points, except as noted, are confirmed
as energy minima on the potential energy surface by vibrational
frequency analysis. The notation G3Large* refers to the use of the
G3Large basis set on key atoms S, O, and N and the use of
6-31G(d) on carbon and hydrogen.
1
tion and quantification were done by a combination of H NMR,
19F-NMR and GC-MS (EI, DB-5 column) on concentrated reaction
mixtures. All compounds, save for trans-3, were compared to
authentic samples. Previous literature41 with both cis and trans
isomers of analogues provided clear precedent for assignment of
1
the aziridine stereochemistry by H NMR.
Materials. Products 7e,65 8e,66 8d,66 10b,67 and 1166 were
prepared using literature methods. The compounds cis-3 were
prepared from 4-octene by analogy for a preparation based on
3-hexene.41 Compound 6b was prepared using a method given for
the benzoyl analogue.68 Its water solubility and relatively high
volatility made purification beyond about 75% difficult, but the
NMR data were clear, and the photolyzates were clearly identified
as identical by spiking the samples with the synthetic mixture.
Similarly, urethane 13, prepared by treatment of isopropoxycarbonyl
imidazole69 with excess methylamine in water, could not be
completely purified, but was spectroscopically and chromatographi-
cally identified. NMR data for previously unreported aziridines and
6b are given in the Supporting Information.
N-Acetyl Dibenzothiophene Sulfilimine, 1b. To a solution of
trifluoroacetic anhydride, (0.14 mL, 1 mmol) in dichloromethane
(40 mL) at -78 °C, was slowly added dibenzothiophene S-oxide
(0.1 g, 0.5 mmol) in dichloromethane (3 mL). After cooling and
stirring at -78 °C for 1 h, powdered acetamide (80 mg, 1.3 mmol)
was added as the solid. After 2 h, the reaction was warmed to -20
°C and then quenched with ice-water. The reaction mixture was
extracted with saturated sodium bicarbonate, and the organic layer
was dried and concentrated to give the crude product. The title
compound was obtained in 30% yield after silica chromatography
with a gradient of ethyl acetate in dichloromethane: 1H NMR
(CDCl3) δ 8.01 (d, J ) 7.2 Hz, 2H), 7.83 (d, J ) 6.9 Hz, 2H),
7.62 (t, J ) 7.8 Hz, 2H), 7.52 (t, J ) 7.5 Hz, 2H), 2.18 (s, 3H);
13C NMR (CDCl3) δ 24.2, 123.7, 129.0, 130.6, 133.3, 138.5, 138.4,
182.2; HRMS calcd for C14H11NOS 241.0561, found 241.0562.
N-Trifluoroacetyl Dibenzothiophene Sulfilimine, 1c. The
compound was prepared as was 1b, save for use of trifluoroaceta-
Steady-State Photolysis Methods. Solvents were spectral grade
and were used without further purification. The quantum yield
measurements were carried using a 75 W Xe arc lamp fitted to a
monochromator set to the specified wavelength with (12 nm linear
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1
mide in place of acetamide: 65% yield; H NMR (CDCl3) δ 8.18
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Malick, D. K. ; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski,
J.; Ortiz, J. V.; Baboul, A. G. ; Stefanov, B. B. ; Liu, G. ; Liashenko, A. ;
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(d, J ) 7.8 Hz, 2H), 7.95 (d, J ) 7.8 Hz, 2H), 7.74 (t, J ) 7.8 Hz,
2H), 7.60 (t, J ) 7.5 Hz, 2H); 13C NMR (CDCl3) δ, 117.1 (q, J )
286.2 Hz), 122.9, 129.28, 130.7, 133.6, 135.9, 138.7, 169.0 (q, J
) 35.3 Hz); HRMS calcd for C14H8F3NOS 295.0279, found
295.0283.
N-Mesyl Dibenzothiophene Sulfilimine, 1d. The procedure
described for 1e was used, save with chloramine M in place of
chloramine T. The crude product was purified using column
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