Desikan et al.
complete conversion. Reactions for product yield determinations
were typically stopped when only a few percent of the original
starting material remained. Identification and quantification were
done by a combination of 1H NMR and GC-MS (EI, DB-5 column)
of crude reaction mixtures. Products were identified by comparison
of data to authentic samples for all compounds except 8b, 9b, and
12b. Compounds 8b and 9b were known in the literature, and the
of the nitrene, still disappears only on the microsecond time
scale. Given the paucity of triplet-derived products, we believe
the major pathway for its decomposition is relatively slow
intersystem crossing to the ground-state singlet. Although
phenylisocyanate is a troublesome byproduct of photolysis of
1
2, this alternate reaction of 2* is obviously dependent on the
presence of the adjacent carbonyl group; thus we conclude that
sulfilimines based on dibenzothiophene are likely to be useful
precursors to a variety of nitrenes. Further work is underway.
1
1
reported H NMR was relied upon.67,68 The H NMR spectrum of
the analogue of 12b made from trans-3-hexene (as opposed to trans-
4-octene) and its analogy to the spectrum and GC-MS of 12a was
used as evidence of structure.
Compound Preparation. N-Benzoyl-S,S-diphenylsulfilimine 1,69
benzoylazide 3,70 carbamate 8a,71 N-methoxybenzamide 9a,71 and
oxadiazole 672 were prepared by literature methods. cis-Aziridine
12a was prepared by the method of Tanner,73 previously applied
Experimental Section
Time-Resolved IR Methods. The TRIR experiments have been
conducted following the method of Hamaguchi and co-workers59,60
as has been described previously.61 Briefly, 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 data process-
ing. The experiment is conducted in dispersive mode.
1
to the hexene derivative, rather than the octene derivative: H NMR
(CDCl3) δ 1.01 (t, J ) 7.2 Hz, 6H), 1.44-1.66 (m, 6H), 1.7-1.8
(m, 2H), 2.52-2.58 (m, 2H), 7.45 (t, J ) 7.6 Hz, 2H), 7.55 (t, J )
7.6 Hz, 1H), 7.99 (d, J ) 7.2 Hz, 2H); 13C NMR (CDCl3) δ 14.0,
20.6, 30.1, 42.3, 128.3, 129.2, 132.5, 133.8, 180.4. Compounds 8b
and 9b were identified by comparison to literature reports of their
1H NMR spectra,67,68 in addition to MS data.
N-Benzoyl-S,S-dibenzothiophene Sulfilimine 2. This compound
was prepared in two ways. Method A was in close analogy to that
of Nakayama.74 To a solution of trifluoroacetic anhydride (0.706
mL, 5.0 mmol) in CH2Cl2 at -78 °C was added dibenzothiophene-
S-oxide11 (0.5 g, 2.5 mmol) in CH2Cl2. The reaction was stirred at
this temperature for 30 min. At -60 °C, a solution of benzamide
in THF (0.606 g, 5.0 mmol) was added, and the reaction was held
at this temperature for 90 min. The reaction mixture was then slowly
warmed to room temperature. The reaction mixture was washed
with saturated sodium bicarbonate, and the organic layer was dried
and concentrated to give the crude product. Purification was by
silica chromatography using 5% EtOAc in CH2Cl2 as eluent to give
2 in 30% yield: 1H NMR (CDCl3) δ 8.26 (d, J ) 7.2 Hz, 2H),
8.13 (d, J ) 6.9 Hz, 2H), 7.95 (d, J ) 7.8 Hz, 2H), 7.69 (t, J ) 7.5
Hz, 2H), 7.56 (t, J ) 7.5 Hz, 2H), 7.3-7.5 (m, 3 H); 13C NMR
(CDCl3) δ 122.3, 127.9, 128.9, 129.0, 129.9, 131.0, 132.4, 135.9,
138.4, 138.4, 178.6; MS (m/z) 303, 274, 200, 184; IR 1592, 1545,
1333, 1292 755, 714 cm-1. Method B: N-p-Tosyldibenzothiophene
sulfilimine was made following the known literature procedure for
related compounds.75 N-p-Tosyldibenzothiophene sulfilimine (1.0
g, 2.8 mmol) was dissolved in 10 mL of concentrated sulfuric acid
(95%) at room temperature for about 2 h, and the resulting solution
was then poured into 100 mL of cold diethyl ether. After removal
of the ether, the oily mixture was dissolved in 100 mL of
chloroform, washed with ammonium hydroxide (2×), followed by
water (5×), dried with sodium sulfate, and the solvent was removed.
The white solid was then dissolved in 50 mL of benzene and added
in benzoic anhydride (0.65 g, 2.8 mmol). The resulting solution
was allowed to stir for 1 h. Then benzene was removed, and the
residue was dissolved 50 mL of dichloromethane, washed with
water (5×), dried with sodium sulfate, and the solvent was removed.
Computational Methods: Geometries were fully optimized at
the respective level of theory, and all stationary points were
confirmed to be energy minima by vibrational frequency
analysis. The B3LYP62-64 calculations were performed with Gauss-
ian 98.65
General Steady-State Photolysis Methods. Solvents used were
“spectral grade” and were used without further purification. The
photolyses and quantum yield measurements were carried using a
75 W xenon Arc lamp fitted to a monochromator set to the specified
wavelength with (12 nm linear dispersion. Valerophenone was used
as the actinometer,66 and the photolysis at 320 nm to form
acetophenone was monitored by HPLC. Samples were placed in a
1 cm square quartz cell mounted on a holder such that all the light
emanating from the monochromator hits the sample directly (OD
> 2). Initial concentrations were 2-4 mM. Except as noted, all
solutions were bubbled with Ar for at least 10 min prior to
photolysis. The progress of reactions was monitored by HPLC
analysis with a diode array UV/vis detector with a C18 reverse
phase column for separation. All reported yield data represent at
least duplicate experiments, and most were carried out in triplicate
or greater.
Quantum yields were measured by monitoring the appearance
of DBT, using HPLC detection and low conversions. Product yields
reported in Table 1 were determined from runs done to nearly
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