Notes
J . Org. Chem., Vol. 63, No. 25, 1998 9531
procedure for 7d and 7e failed even using 1 equiv of oximes 4d
or 4e; therefore, their selected spectral data were deduced by a
careful analysis of the 1H and 13C NMR spectra of the related
crude mixtures, after the signals of the other products were
subtracted, and by comparison with data of 7f.
and an intense purple color appeared in the first one. No color
appeared when the photooxygenation was carried out in the
absence of either oxime 4b or furan 1a .
When the above procedure was carried out using acetone
oxime (4c), the same results were obtained.
Decom p osition of Tr ioxa zin e 6b in th e P r esen ce of 2,3-
Dim eth ylbu t-2-en e. A 2 × 10-2 M solution of 1a (0.25 mmol)
and 4b (0.25 mmol) in CDCl3 was photooxygenated at -20 °C
as above. After 90 min, the 1H NMR, recorded at this temper-
ature, showed the presence of only trioxazine 6b. The solution
was carefully degassed with dry N2, and 2,3-dimethylbut-2-ene
(1.25 mmol), precooled at -20 °C, was then added. The resulting
mixture was allowed to stand at room temperature. After 30
min the 1H NMR showed that only keto ester 8 and ketone 9b
were formed in ca. 1:1 molar ratio. No evidence was obtained
to indicate the presence of any alkene-HNO adduct.14
P r oced u r e for 18O2 Oxygen a tion of F u r a n 1a in th e
Ben za ld eh yd e oxim e O-[1-h yd r op er oxy-3,3-(d im eth oxy-
ca r bon yl)-1-p h en yl-2-p r op en yl] eth er (7d ):12 1H NMR δ 3.78
(s 3 H), 3.83 (s, 3 H), 7.23 (s, 1 H), 8.28 (s, 1 H), 9.49 (brs, 1 H);
13C NMR δ 52.4, 52.7, 107.8, 142.5, 152.5, 163.6, 166.4.
Acetop h en on e oxim e O-[1-h yd r op er oxy-3,3-(d im eth oxy-
ca r bon yl)-1-p h en yl-2-p r op en yl] eth er (7e):12 1H NMR δ 2.41
(s, 3 H), 3.77 and 3.78 (2s, 6 H), 7.24 (s, 1 H); 13C NMR δ 13.5,
52.3, 52.6, 107.7, 142.9, 158.6, 163.6, 165.8.
Ben zop h en on e oxim e O-[1-h yd r op er oxy-3,3-(d im eth ox-
yca r bon yl)-1-p h en yl-2-p r op en yl] eth er (7f): 40% yield; white
foam; IR 3512, 3286, 1735, 1658 cm-1; 1H NMR δ 3.45, (s, 3 H),
3.77 (s, 3 H), 7.20-7.60 (m, 16 H), 9.83 (brs, 1 H); 13C NMR δ
52.1, 52.7, 108.2, 126.8, 128.1, 128.3, 128.7, 129.3, 129.5, 129.7,
130.1, 132.4, 135.7, 136.1, 142.9, 160.6, 163.6, 165.7. Anal.
Calcd for C26H23NO7: C, 67.67; H, 5.02; N, 3.04. Found: C, 67.4;
H, 5.1; N, 3.1.
Gen er a l P r oced u r e for th e TP P -Sen sitized P h otooxy-
gen a tion of F u r a n 1a in th e P r esen ce of Oxim es 4a ,b in
CF Cl3-CDCl3. Each solution (5 × 10-2 M) of the furan 1a (0.5
mmol) and the oximes 4a ,b (2.5 mmol) in CFCl3-CDCl3 (1:1 v/v),
after the addition of the sensitizer (TPP 1.8 × 10-4 mmol), was
photooxygenated at -75 °C as reported above. When the
reaction was complete (90 min), for entry a , the 1H NMR
spectrum recorded at -70 °C showed, in addition to unreacted
oxime 4a , the presence of 7a which rapidly converted to
trioxazine 6a as a mixture of two conformational isomers. The
latter upon warming to -10 °C led to nitrone 5a , keto ester 8
and a mixture of acetaldehyde and aldehyde-related unidentified
compounds in ca. 5:1:1 molar ratio. For entry 2, the 1H NMR
spectrum recorded at -70 °C showed, in addition to unreacted
oxime 4b, the presence of endo-peroxide 2a which was identified
by comparison with an authentic sample.34 Upon warming to
-50 °C, a complex mixture was formed which evolved continu-
ously leading to only trioxazine 6b as a mixture of two confor-
mational isomers. The latter coalesced at -10 °C and, at 0 °C,
led to keto ester 8 and an unidentified compound which in turn
converted into ketone 9b.16 After 90 min compounds 8 and 9b
were present in ca. 1:1 molar ratio. Selected spectral data of
oxime ether 7a and trioxazines 6a ,b were deduced by a careful
analysis of the 13C and 1H NMR spectra of the related reaction
mixtures, recorded at -70 and -50 °C, respectively, after the
signals of the other products were subtracted. It was not
possible to run satisfactory 13C NMR spectrum for 7a owing to
its fast rearrangement into trioxazine 6a even at -70 °C.
Aceta ld eh yd e oxim e O-[1-h yd r op er oxy-3,3-(d im eth oxy-
car bon yl)-1-ph en yl-2-pr open yl] eth er (7a):12 1H NMR (CFCl3-
CDCl3) δ 2.28 (d, J ) 5.7 Hz, 3 H), 3.46 (s, 3 H), 3.83 (s, 3 H),
13.10 (brs, 1 H).
Meth yl 2-(m eth oxycar bon yl)-3-(dih ydr o-6-m eth yl-3-ph en -
yl-1,2,4,5-tr ioxa zin -3-yl)p r op en oa te (6a ) (tw o isom er s): 1H
NMR (CFCl3-CDCl3) δ 1.37 and 1.40 (2d, J ) 5.9 Hz, 6 H), 3.70,
3.77, 3.78 and 3.86 (4s, 12 H), 4.71 (q, J ) 5.9 Hz, 1 H), 4.88 (q,
J ) 5.9 Hz, 1 H), 6.99 and 7.16 (2s, 2 H), 7.26 (brs, 1 H), 7.27-
7.56 (m, 10 H), 7.88 (brs, 1 H); 13C NMR (CFCl3-CDCl3) δ 10.8,
13.9, 53.0, 53.2, 93.4, 100.0, 102.1, 105.4, 137.3, 140.1, 163.5,
163.7, 166.6, 168.3.
Meth yl 2-(m eth oxyca r bon yl)-3-(3-p h en yl-1,2,4-tr iox-5-
a za sp ir o[5.5]u n d ec-3-yl)p r op en oa te (6b) (tw o isom er s): 1H
NMR (CFCl3-CDCl3) δ 3.69, 3.73, 3.77 (two overlapping s)
(together 12 H), 6.96 and 7.15 (2s, 2 H), 7.20-7.57 (m, 10 H),
9.57 (brs, 2 H); 13C NMR (CFCl3-CDCl3) δ 52.8, 53.0, 101.2,
102.4, 103.8, 106.5, 143.2, 145.9, 161.2, 163.9, 166.9.
P r oced u r e for Gr iess Test. A 2 × 10-2 M solution of 1a
(0.5 mmol) and cyclohexanone oxime (4b) (0.5 mmol) in CH2Cl2
at -20 °C was photooxygenated as above, and the gas which
came out from the reaction apparatus was passed through two
traps containing 0.017 M NaOH (20 mL). A Griess reagent (2
mL) was added after 90 min to a sample (25 µL) from each trap,
P r esen ce of Cycloh exa n on e Oxim e (4b). A 2 × 10-2
M
solution of 1a (0.25 mmol) and 4b (0.25 mmol) in CH2Cl2, after
the addition of TPP (1.8 × 10-4 mmol), was saturated with 18O2
and irradiated at -20 °C. When the reaction was complete (240
min, TLC), the solution was concentrated under N2 and chro-
matographed on silica gel using CH2Cl2 as eluent. The two
fractions containing the ketone 9b and keto ester 8, respectively
(TLC), were directly analyzed by MS. The spectra of both
compounds showed that the parent and fragmentation peaks
were accompanied by isotopic peaks at +2 Da more intense than
those found for the unlabeled reference compounds.
Et2S Red u ction of Oxim e Eth er Hyd r op er oxid e 7f.
A
solution of 7f (116 mg, 0.25 mmol) in CCl4 (5 mL) was treated
with Et2S (34 mg, 0.37 mmol). When the reduction was complete
(30 min), the 1H NMR showed the presence of keto ester 8 and
oxime 4f in 1:1 molar ratio in addition to Et2S and Et2SO.
Removal of the solvent and of the unreacted Et2S gave a residue
that was chromatographed on silica gel using light petroleum/
ether (9:1, 8:2) as eluent and gave oxime 4f (48 mg, 98%) and
keto ester 8 (60 mg, 97%), successively.
Th er m olysis of Oxim e Eth er Hyd r op er oxid e 7f. Com-
pound 7f (0.1 mmol, 46 mg) was refluxed in dry benzene (5 mL).
After 1 h the 1H NMR spectrum showed 7f almost unchanged.
Heating for a further 15 h resulted in the complete disappear-
ance of the original compound, and keto ester 8 and benzophe-
none (9f) were present in ca. 1:1 molar ratio in addition to a
certain amount of unidentified products.
On e-P ot Syn t h esis of N-(H yd r op er oxya lk yl)k et on i-
tr on es 5. Each solution of the furan (0.5 mmol) and oxime (2.5
mmol) in CH2Cl2 (25 mL) was photooxygenated at -20 °C as
above. After completion of reaction (90 min, 1H NMR), the
solvent was removed under reduced pressure and the residue
was chromatographed on a short column of silica gel. Elution
with light petroleum/ether (8:2, 1:1) gave mixtures of unreacted
oxime and keto ester 8 and pure hydroperoxy nitrones 5,
successively.
(E)-1-Hyd r op er oxy-N-[3,3-(d im eth oxyca r bon yl)-1-p h en -
yl-2-p r op en ylid en e]p r op yla m in e N-oxid e (5b): 54% yield;
mp 75-76 °C (from diethyl ether-hexane); IR 3518, 3085, 1737,
1
1603, 1236 cm-1; H NMR δ 0.86 (t, J ) 7.3 Hz, 3 H), 1.86 (m,
J ) 7.3, 6.2 Hz, 2 H), 3.19 (s, 3 H), 3.79 (s, 3 H), 5.61 (t, J ) 6.2
Hz, 1 H), 7.30-7.60 (m, 5 H), 8.15 (s, 1 H), 10.89 (brs, 1 H); 13
C
NMR δ 8.8, 23.8, 52.0, 52.8, 99.7, 128.7, 129.6, 130.3, 130.8,
132.3, 146.7, 164.1, 164.2. The signal of a carbon is hidden in
the aromatic resonances. Anal. Calcd for C16H19NO7: C, 56.97;
H, 5.68; N, 4.15. Found: C, 56.6; H, 5.8; N, 3.9.
(E)-1-Hydr oper oxy-2-m eth yl-N-[3,3-(dim eth oxycar bon yl)-
1-p h en yl-2-p r op en ylid en e]p r op yla m in e N-oxid e (5c): 34%
yield; mp 60-62 °C (from diethyl ether-hexane); IR 3511, 3154,
1733, 1604, 1245 cm-1 1H NMR δ 0.85 and 0.93 (2d, J ) 6.9
;
Hz, 6 H), 2.28 (m, J ) 8.8, 6.9 Hz, 1 H), 3.17 (s, 3 H), 3.76 (s, 3
H), 5.37 (d, J ) 8.8 Hz, 1 H), 7.35-7.50 (m, 5 H), 8.16 (s, 1 H),
11.57 (brs, 1 H); 13C NMR δ 18.0, 18.2, 29.7, 52.0, 52.7, 103.2,
128.6, 129.8, 130.2, 131.2, 132.3, 132.6, 147.3, 164.1, 164.2.
Anal. Calcd for C17H21NO7: C, 58.11; H, 6.02; N, 3.99. Found:
C, 58.3; H, 5.8; N, 4.0.
(E)-1-Hyd r op er oxy-N-[3,3-(d im eth oxyca r bon yl)-1-p h en -
yl-2-p r op en ylid en e]h ep tyla m in e N-oxid e (5d ): 35% yield;
oil; IR 3504, 3145, 1734, 1601, 1260 cm-1; 1H NMR δ 0.40-2.00
(m, 13 H), 3.17 (s, 3 H), 3.79 (s, 3 H), 5.65 (t, J ) 6.4 Hz, 1 H),
(34) Iesce, M. R.; Graziano, M. L.; Cermola, F.; Cimminiello, G.;
Scarpati, R. Gazz. Chim. Ital. 1990, 120, 629.