Trapping of Cyclopropenyl Radicals
J . Org. Chem., Vol. 64, No. 14, 1999 5099
F igu r e 4. Plausible mechanism for the EPR generation and trapping of cyclopropenyl radicals from N-(2-cyclopropenylcarbo-
nyloxy)phthalimides 1 or cyclopropenes 3, respectively.
105.72 (C), 18.90 (CH). Anal. Calcd for C24H15NO4: C, 75.58;
H, 3.96; N, 3.67; O, 16.78. Found: C, 75.65; H, 4.09; N, 3.61.
1-Bu tyl-2-p en tylcyclop r op en e (3a ). This compound was
prepared as previously reported in ref 6 starting from 143 mg
(0.6 mmol) of ethyl 2-butyl-3-pentyl-2-cyclopropenecarboxylate.
Pure cyclopropene 3a (51,5 mg, 0.31 mmol, 52%) was thus
obtained after flash chromatography with hexane/diethyl ether
129.22 (CH), 128.80 (CH), 127.10 (C), 107.58 (C), 60.33 (CH2),
21.65 (CH), 14.36 (CH3). Anal. Calcd for C18H16O2: C, 81.79;
H, 6.10; O, 12.11. Found: C, 81.66; H, 6.24.
1,2-Dip h en ylcyclop r op en e (3f). This compound was pre-
pared as previously reported in ref 6 starting from 1.55 g (6.77
mmol) of 1-chloro-1,2-diphenylcyclopropane. Pure 1,2-diphe-
nylcyclopropene 3f (975 mg, 5.07 mmol, 75%) was thus
obtained after flash chromatography with hexane. IR (film):
3078, 3058, 3028, 3022, 2952, 2867, 1820, 1596, 1494, 1444,
1020, 752, 686. 1H NMR (300 MHz): 7.73-7.69 (m, 4H), 7.44-
7.28 (m, 6H), 1.55 (s, 2H). 13C NMR (75 MHz): 130.06 (C),
129.66 (CH), 128.54 (CH), 128.14 (CH), 111.65 (C), 6.32 (CH2).
Anal. Calcd for C15H12: C, 93.71; H, 6.29. Found: C, 93.62; H,
6.38.
1
(9:1). IR (film): 2958, 2929, 2860, 1465, 1379, 1010. H NMR
(300 MHz): 2.38 (t, 4H), 1.60-1.48 (m, 4H), 1.36-1.22 (m, 6H),
0.94-0.82 (m, 6H), 0.77 (s, 2H). 13C NMR (75 MHz): 109.37
(C), 109.32 (C), 31.61 (CH2), 29.70 (CH2), 29.54 (CH2), 27.06
(CH2), 25.73 (CH2), 25.61 (CH2), 22.45 (CH2), 14.02 (CH3), 13.84
(CH3), 7.36 (CH2). Anal. Calcd for C12H22: C, 86.67; H, 13.33.
Found: C, 86.63; H, 13.37.
7,8-Meth ylen e-7-tetr a d ecen oic Acid (3b) a n d 7,8-Ca r -
boxym eth ylen e-7-tetr a d ecen oic Acid (3c). These products
were prepared as described in ref 6.
Ack n ow led gm en t. We are grateful to professor L.
Eberson and Dr. G. Fabria`s for their helpful comments
and to Dr. Ll. Fajar´ı for preliminary EPR experiments.
The authors express their gratitude to the EPR service
of (CID-CSIC) in Barcelona for all of the facilities offered
in obtaining the EPR spectra presented here and to the
National Institute of Environmental Health Science
(USA) for providing us with the WINSIM program to
simulate EPR spectra. Financial support from CICYT
(project AGF98-0844), DGICYT (project PB96-0836),
Generalitat de Catalunya (grant 97SGR-0021), and
SEDQ, S.A. is also acknowledged. M.C. thanks the
Spanish Ministerio de Educacio´n y Cultura for a pre-
doctoral fellowship.
2,3-Diph en yl-2-cyclopr open ecar boxylic Acid (3d). Treat-
ment of ethyl 2,3-diphenyl-2-cyclopropenecarboxylate 3e (265
mg, 1 mmol) with a 1 N solution of KOH in THF/MeOH/H2O
(2:1:1) (20 mL) at room temperature for 48 h gave a crude that
was purified by flash chromatography on deactivated silica gel
to afford pure 3d (224 mg, 95%). IR (film): 3600-3200, 3060,
1
3029, 2960, 2927, 1703, 1498, 1446, 1224, 757, 692. H NMR
(300 MHz): 7.73-7.65 (m, 4H), 7.54-7.35 (m, 6H), 2.81 (s,
1H). 13C NMR (50 MHz): 180.03 (C), 129.96 (CH), 129.50 (CH),
128.92 (CH), 126.66 (C), 107.09 (C), 21.11 (CH). Anal. Calcd
for C16H12O2: C, 81.34; H, 5.12; O, 13.54. Found: C, 81.53; H,
5.36.
Eth yl 2,3-Dip h en yl-2-cyclop r op en eca r boxyla te (3e).
This compound was prepared as previously reported,6 starting
from 2.34 g (13.1 mmol) of diphenylacetylene, 0.5 g of activated
Cu-bronze, and 2.76 mL (26.3 mmol) of ethyl diazoacetate.
Pure ester 3e (1,93 g, 7.3 mmol, 56%) was obtained after flash
chromatography with hexane/ethyl acetate (95:5). IR (film):
3083, 3064, 3033, 3026, 2981, 2960, 1728, 1720, 1496, 1446,
1251, 1180, 1172, 1039, 1010, 688. 1H NMR (300 MHz): 7.75-
7.64 (m, 4H), 7.53-7.37 (m, 6H), 4.20 (q, 2H), 2.84 (s, 1H),
1.26 (t, 3H). 13C NMR (75 MHz): 174.79 (C), 129.86 (CH),
Su p p or t in g In for m a t ion Ava ila b le: Copies of EPR
spectra for the spin adducts of cyclopropene derivatives 1a ,
3a , 3b , 3e, and di-tert-butylperoxide with DMPO. This
material is available free of charge via the Internet at
http://pubs.acs.org.
J O9900026