Dolbier et al.
with AF4-acetamide (6) (0.205 g, 0.50 mmol), 5 mL of n-butyl
ether, and 1-octene (7.85 mL, 50.0 mmol, 100 equiv). This mixture
was heated to 110 °C and the PCBN (0.16 g, 0.85mmol) in 10 mL
of n-butyl ether was added over a period of 30 min. The reaction
mixture was then maintained at this temperature overnight, after
which the mixture was cooled and solvent evaporated under
vacuum. The residue was subjected to chromatography on a silica
gel column, which was eluted with hexanes/ethyl acetate (100:1)
to give 0.21 g of the oily ene product 10 (86%), as a 2.4:1 ratio of
trans to cis isomers.
(Scheme 10) demonstrated clearly that loss of N2 (Ea < 1 kcal/
mol) will dominate any such hypothetical cyclization (Ea ) 40.6
kcal/mol) to form diazene 20, which was shown not to be an
intermediate, but rather a transition state for the 1,2-shift of
(-NtN)+.
Thus the mechanistic puzzle remains unsolved as this paper
is written. Both computational and experimental efforts toward
a resolution of this issue continue.
Trans isomer: 19F NMR (eight equal intensity AB doublets) δ
-110.6 (d, J ) 243 Hz), -113.5 (d, J ) 243 Hz), -114.8 (d, J )
239 Hz), -115.8 (d, J ) 236 Hz), -117.5 (d, J ) 242 Hz), -117.6
(d, J ) 238 Hz), -118.8 (d, J ) 239 Hz), -119.0 (d, J ) 240
Hz).
Experimental Section
General Information. 1H and 13C chemical shift data are directly
indicated on the structures of the respective adducts provided either
in the Results and Discussion Section or in the Experimental
Section, whereas 19F NMR data are provided in the Experimental
Section below. When mixtures of products were analyzed, products
were characterized by H1-C13 couplings as seen in the GHMQC
and GHMBC spectra. A full description of such analyses can be
found in the Supporting Information. Additional details regarding
1H spectra, including coupling constants, may be found in the
Supporting Information.
p-Chlorobenzoyl Nitrite (PCBN). Following the literature
method,9 to a sodium bicarbonate solution (9.0 g, 0.11mol) in water
was added 4-chlorobenzoic acid (17 g, 0.12 mol). The solution was
filtered hot and to the filtrate was added silver nitrate (19 g,
0.11mol) in water during stirring. The precipitated silver p-
chlorobenzoate was filtered and washed with ethanol (twice) and
dried over P2O5 under vacuum for 1 day.
Cis isomer: 19F NMR (eight equal intensity AB doublets)
δ -111.1 (d, J ) 245 Hz), -113.5 (d, J ) 245 Hz), -114.9 (d, J
) 240 Hz), -115.8 (d, J ) 236 Hz), -117.5 (d, J ) 242 Hz),
-117.6 (d, J ) 238 Hz), -118.9 (d, J ) 240 Hz), -119.1 (d, J )
239 Hz).
Cis,trans mixture: MS(EI) m/z 462(M+)(15), 391(16), 365(17),
189(45), 215(19), 176(100); HRMS calcd for C24H22F8 462.1594,
found 462.1593 (EI). Anal. Calcd for C24H22F8: C, 62.34; H, 4.795.
Found: C, 62.42; H, 5.01.
To a stirred suspension of silver p-chlorobenzoate (20 g, 75
mmol) in 180 mL of dry CCl4 at -10 °C was added nitrosyl
chloride (NOCl) (8 g, 125mmol) during 30 min. The mixture was
stirred for a further 20 min at -10 °C and 1 h at room temperature.
The mixture was filtered rapidly after that and the residue was
washed with CCl4 twice. The filtrates were combined and evapo-
rated under vacuum. The residue was distilled under vacuum (84-
85 °C/2.5 mmHg) to give 12.1 g of a yellow-reddish solid (86%).
The product (PCBN) was made into a 0.86 M solution in benzene
or n-butyl ether for future use, and this solution was refrigerated
until needed.
4-Acetamido-1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane
(6) (AF4-acetamide) was prepared as previously reported.22
Reaction of AF4-Acetamide 6 with Anthracene under Ca-
dogan Conditions. A 50-mL three-necked round-bottom flask was
charged with AF4-acetamide 6 (0.205 g, 0.500 mmol), 5 mL of
n-butyl ether, and anthracene (0.18 g, 1.00 mmol, 2.00 equiv). This
mixture was heated to 110 °C and PCBN (0.16 g, 0.85mmol) in
10 mL of n-butyl ether was added over a period of 30 min. The
reaction mixture was maintained at this temperature overnight. Then
the mixture was cooled and the solvent evaporated under vacuum.
The residue was purified on a silica gel column, eluting with
hexanes/ethyl acetate (100:1) to give the white crystalline Diels-
Alder, 9,10-adduct 5 in yields that were consistently about 95%,
Reaction of Cyclopentene with AF4-Acetamide under Ca-
dogan Conditions. The procedure was the same as above except
that cyclopentene (10 equiv) was the reactant. The yield was 53%
with two stereoisomers 11a and 11b in a ratio of 5.6:1.
Isomer 11a: 19F NMR (eight AB doublets, although the signals
at 116.90 and 116.94 are apparent broad singlets, with barely
detectable AB sidebands) δ 109.8 (d, J ) 245 Hz), 112.6 (d, J )
243 Hz), 116.9 (apparent br s, with detectable AB sideband with
JAB ) 243), 116.94 (br s, JAB obscured), 117.0 (d, J ) 239 Hz),
117.6 (d, J ) 241 Hz), 119.6 (d, J ) 238 Hz), 119.7 (d, J ) 242
Hz).
1
with less than 3% of the 1,4 adduct being detected. H, 13C, and
19F NMR spectra of 5 were consistent with those reported
previously.15
Reaction of AF4-Acetamide (6) with Naphthalene and Ben-
zene under Cadogan Conditions. The analogous reaction with
naphthalene proceeded similarly giving consistent total yields of
endo- and exo-adducts in the range of 93%, the major product being
endo-8 along with 15-17% of the exo-product. When the reaction
was carried out in refluxing benzene with no other substrate, the
benzene adduct 7 was obtained in 90% yield. 1H, 13C, and 19F NMR
spectra of 7 and 8 were consistent with those reported previously.15
1-Octene Reaction with AF4-Acetamide under Cadogan
Conditions. A 50-mL three-necked round-bottom flask was charged
Isomer 11b: 19F NMR (two AB doublets along with six apparent
singlets) δ 107.8 (d, JAB ) 243 Hz), 112.8 (d, JAB ) 243 Hz),
115.6 (br s), 115.6 (br s), 117.7 (s), 117.8 (s), 118.3 (s), 118.4 (s).
Mixture of 11a and 11b: MS(EI) m/z 418 (M+) (33), 242 (100),
176 (28). HRMS calcd for C21H14F8 418.0967, found 418.0942 (EI).
Anal. Calcd for C21H14F8: C, 60.29; H, 3.37. Found: C, 60.08; H,
3.38.
Reaction of Cyclohexene with AF4-Acetamide (6) under
Cadogan Conditions. The procedure was the same as above except
that cyclohexene (10 equiv) was the reactant. The product, which
(22) Roche, A. J.; Dolbier, W. R., Jr. J. Org. Chem. 1999, 64, 9137-
9143.
556 J. Org. Chem., Vol. 72, No. 2, 2007