Stereospecific alkenylation of C-H bonds via reaction with β- heteroatom-functionalized trisubstituted vinyl triflones

Article abstract of DOI:10.1021/ja963636s

Aryl and alkyl β-heteroatom-trisubstituted vinyl triflones react with THF and cyclohexane to undergo trifluoromethyl radical-mediated C-H functionalization reactions to afford E and Z β-heteroatom-trisubstituted olefins. Most reactions proceed with both high yield and high stereospecificity (retention of configuration). β-Substituents which have been employed in this study are iodine, bromine, fluorine, benzoate, ethylcarbonate, and phthalimide. β-Substituents bearing powerful electron- releasing groups such as alkoxy or amino render the vinyl triflone unreactive.

Full text of DOI:10.1021/ja963636s

J. Am. Chem. Soc. 1997, 119, 4123-4129
4123
Stereospecific Alkenylation of C-H Bonds via Reaction with
â-Heteroatom-Functionalized Trisubstituted Vinyl Triflones1
Jason Xiang, Wanlong Jiang, Jianchun Gong, and P. L. Fuchs*
Contribution from the Department of Chemistry, Purdue UniVersity,
West Lafayette, Indiana 47907
ReceiVed October 18, 1996X
Abstract: Aryl and alkyl â-heteroatom-trisubstituted vinyl triflones react with THF and cyclohexane to undergo
trifluoromethyl radical-mediated C-H functionalization reactions to afford E and Z â-heteroatom-trisubstituted olefins.
Most reactions proceed with both high yield and high stereospecificity (retention of configuration). â-Substituents
which have been employed in this study are iodine, bromine, fluorine, benzoate, ethylcarbonate, and phthalimide.
â-Substituents bearing powerful electron-releasing groups such as alkoxy or amino render the vinyl triflone unreactive.
We recently reported that reaction of ethers and hydrocarbons
with di- and trisubstituted vinyl and dienyl triflones such as
(Z)-1 and (E)-1 provides ready access to trisubstituted olefins
and dienes (Scheme 1).2 The reaction proceeds through radical
C-H abstraction3 by the very electrophilic trifluoromethyl
radical (4)4,5 in a process involving addition of the thus-
generated alkyl radical 5 to the R-carbon of the vinyl triflone 1
followed by elimination of the (trifluoromethyl)sulfonyl radical
(3) to afford alkenes 6 and 7 by a unimolecular chain transfer
process (UMCT6). Entropy-promoted fragmentation7 of 3 to
sulfur dioxide and the highly reactive trifluoromethyl radical
(4) (a second UMCT reaction) efficiently propagates the chain.8
The stereospecificity of the sequence is related to both the
stability of the intermediate radical (Z)-2 or (E)-2 and the
possibility of reVersible addition of 3 to the olefinic product.
Unfortunately, the reactions exhibited only modest (∼3-5:1)
stereospecificity in favor of retention of the vinyl triflone
stereochemistry.
Scheme 1
Scheme 2
Since the synthesis of trisubstituted vinyl triflones used in
the above study involved the trans-addition of HI9 (also facile
and high-yielding for addition of HBr and HF10) to acetylenic
triflones 8a,b8a followed by Stille coupling, we considered the
possibility of achieving a stereospecific C-H alkenylation
reaction by inVersion of the reaction order. If â-iodovinyl
X Abstract published in AdVance ACS Abstracts, April 1, 1997.
(1) Syntheses Via Vinyl Sulfones. 69. Triflone Chemistry. 8.
(2) Xiang, J., Fuchs, P. L. J. Am. Chem. Soc. 1996, 118, 11986.
(3) Medebielle, M.; Pinson, J.; Saveant, J.-M. J. Am. Chem. Soc. 1991,
113, 6872.
(4) The bond dissociation energy of HCF3 is 107 kcal/mol: In Handbook
of Chemistry and Physics, 74th ed.; Lide, D. R., Ed.; CRC Press, Inc.: Boca
Raton, FL, 1993-1994, pp 9-137.
(5) For a comprehensive review on the chemistry of fluoroalkyl radicals,
see: Dolbier, W. R., Jr. Chem. ReV. 1996, 96, 1557.
(6) For an excellent discussion of the advantage of exploiting radical
reactions which involve unimolecular propagation steps, see: Curran, D.
P.; Xu, J.; Lazzarini, E. J. Chem. Soc., Perkin Trans. 1 1995, 3049.
(7) (a) Langlois, B. R.; Laurent, E.; Roidot, N. Tetrahedron Lett. 1992,
33, 1291. (b) Hu, C. -M.; Qing, F. -L.; Huang, W. -Y. J. Org. Chem. 1991,
56, 2801. (c) Huang, W. -Y.; Hu, L. -Q. J. Fluorine Chem. 1989, 44, 25.
(d) Langlois, B. R.; Laurent, E.; Roidot, N. Tetrahedron Lett. 1991, 32,
7525.
(8) For mechanistic studies and C-H functionalization reactions of
alkynyl triflones, see: (a) Gong, J.; Fuchs, P. L. J. Am. Chem. Soc. 1996,
118, 4486. (b) Xiang, J.; Fuchs, P. L. Tetrahedron Lett. 1996, 37, 5269. (c)
For aldehyde C-H functionalization reactions with alkynyl triflones, see:
Gong, J.; Fuchs, P. L. Tetrahedron Lett. 1997, 38, 787.
(9) Xiang, J.; Mahadevan, A.; Fuchs, P. L. J. Am. Chem. Soc. 1996,
118, 4284.
triflones (Z)-9aI and (Z)-9bI would afford vinyl iodides (Z)-
10aI and (Z)-10bI (Scheme 2), the synthesis of trisubstituted
olefins could then be achieved with a final Stille coupling.
Reaction of â-iodovinyl triflone (Z)-9aI with tetrahydrofuran
or cyclohexane generates vinyl iodide (Z)-10aI11 or (Z)-11aI11
in high yield and with superb stereospecificity as assayed by
HPLC (Scheme 3 and Table 1, entries 1 and 2). As expected
from our observations with acetylenic triflone chemistry, where
phenylethynyl triflone (8a) is about a factor of 5 more reactive
than n-octynyl triflone (8b),8a treatment of alkyl-substituted
â-iodovinyl triflone (Z)-9bI more slowly generates vinyl iodides
(Z)-10bI12 and (Z)-11bI,12 but the stereospecificity remains very
good (Scheme 3 and Table 1, entries 5 and 6). Reaction of the
isomeric â-iodovinyl triflones (E)-9aI9 and (E)-9bI9 is more
problematic due to competitive deiodination of the product vinyl
iodides (E)-10aI, (E)-10bI,12 (E)-11aI, and (E)-11bI12 by
reaction of the products with tetrahydrofuranyl and cyclohexyl
radicals (Schemes 3 and 4 and Table 1, entries 3, 4, 7, and 8).
This difficulty is especially severe in the case of alkenylation
(10) See the Experimental Section for the preparation of bromides (Z)-
9aBr and (Z)-9bBr and fluorides (Z)-9aF and (Z)-9bF.
S0002-7863(96)03636-0 CCC: $14.00 © 1997 American Chemical Society

4124 J. Am. Chem. Soc., Vol. 119, No. 18, 1997
Xiang et al.
Scheme 3
Scheme 5
the product vinyl iodide (Z)-11aI kinetically inert toward
deiodination (Schemes 3 and 4 and Table 1, entry 1).
Reasoning that the unwanted radical-mediated deiodination
of the (E)-vinyl iodides (E)-10aI, (E)-10bI, (E)-11aI, and (E)-
11bI was a consequence of the relatively weak carbon-iodine
bond, we briefly examined the stereospecificity of C-H
alkenylation reactions of â-bromovinyl triflones (Z)-9aBr and
(E)-9aBr. Synthesis of (Z)-9aBr was smoothly and stereospe-
cifically accomplished in 88% yield by reaction of phenylacety-
lenic triflone 8a (the analogous chemistry of n-octynyl triflone
(8b) was not explored) in THF with lithium bromide and
trifluoroacetic acid (similar reactions of acetic acid being too
slow). Preparation of a sample of the isomeric â-bromovinyl
triflone (E)-9aBr was easily achieved by separating a 1:1
mixture of the two isomers which was established via photo-
chemical equilibration (Scheme 5). As expected, radical-
mediated dehalogenation was not a problem with either (Z)- or
(E)-â-bromovinyl triflone, as both (Z)-9aBr and (E)-9aBr
smoothly underwent the alkenylation reaction in uniformly high
yield with stereospecificities ranging from 21:1 to 75:1 for
retention of stereochemistry (Scheme 6 and Table 1, entries
9-12).
Table 1. C-H Alkenylation Reactions of â-Halovinyl Triflones
yield
(%)
Z:E
ratiob
run substrate
conditionsa
THF, 1 d
products
1
2
3
4
5
6
7
8
9
(Z)-9aI
(Z)-9aI
(E)-9aI
(E)-9aI
(Z)-9bI
(Z)-9bI
(Z)-10aI + (E)-10aI
91 67:1
74 79:1
49c 1:6c
c-C6H12, 2 d (Z)-11aI + (E)-11aI
THF, 1 d
c-C6H12, 20 h (Z)-11aI + (E)-11aI
THF, 6 d (Z)-10bI + (E)-10bI
c-C6H12, 4 d (Z)-11bI + (E)-11bI
(Z)-10bI + (E)-10bI
(E)-9bI c-C6H12, 4 d (Z)-11bI + (E)-11bI
(Z)-9aBr THF, 5 h
(Z)-10aI + (E)-10aI
30d >25:1d
55 177:1
81 13:1
59e 1:>100e
50f 1:9f
(E)-9bI THF, 6 d
(Z)-10aBr + (E)-10aBr 90 75:1
10 (Z)-9aBr c-C6H12, 8 h (Z)-11aBr + (E)-11aBr 93 38:1
11 (E)-9aBr THF, 8 h (Z)-10aBr + (E)-10aBr 82 1:21
12 (E)-9aBr c-C6H12, 5 h (Z)-11aBr + (E)-11aBr 80 1:32
Since fluorine-substituted materials are highly prized in the
realm of medicinal chemistry,13 we next turned our attention to
13 (Z)-9aF THF, 13 h
14 (Z)-9aF c-C6H12, 2 d (Z)-11aF + (E)-11aF
15 (E)-9aF THF, 8 h (Z)-10aF + (E)-10aF
16 (E)-9aF c-C6H12, 15 h (Z)-11aF + (E)-11aF
17 (Z)-9bF c-C6H12, 2 d (Z)-11bF + (E)-11bF
18 (E)-9bF c-C6H12, 2 d (Z)-11bF + (E)-11bF
(Z)-10aF + (E)-10aF
82 77:1
98 >100:1
91 1:3
(11) Since there was no clear relationship between the vinyl proton
chemical shift of the vinyl halides as a function of their stereochemistry
(see below), we based the stereochemical assignment of the phenyl-
substituted vinyl halides shown below upon t-BuLi metalation-H2O
quenching reactions of (Z)-10aI, (Z)-11aI, and (E)-10aI which quantitatively
and stereospecifically afforded the disubstituted styrene derivatives with
JHCCH ) 16, 16, and 11.5 Hz, respectively. Such metalations are known to
occur with retention of stereochemistry (Davis, F. A.; Lal, G. S.; Wei, J.
Tetrahedron Lett. 1988, 29, 4269 and references cited therein). The vinyl
bromide and vinyl fluoride stereochemistry was assigned by mechanistic
analogy, but was further verified in the case of the vinyl fluorides by noting
the three-bond JHCCF coupling constants shown below (for typical fluo-
roolefin assignments using JHCCF coupling constants, see: Jackman, L. M.;
Sternhell, S. Applications of Nuclear Magnetic Resonance Spectroscopy in
Organic Chemistry; Pergamon Press: Oxford, 1969; pp 348-350 and
references cited therein).
96 1:8
0
0
NR
NR
a AIBN (15 mol %), solvent at reflux. b Product ratios of >10:1 were
assigned by analytical HPLC. Product ratios of <10:1 were assigned
by NMR integration of the crude reaction mixture. NR ) no reaction.
c The trans-cinnamyl derivative of THF (deiodinated 10a) was also
isolated in 25% yield from this reaction (cf. Scheme 4). d A 60% yield
of a 1:1 mixture of Z-13 and (E)-13 admixed with 50% cyclohexyl
iodide (12) was also isolated from this reaction (see Scheme 4). e Yield
based upon 30% recovered starting triflone (E)-9bI. f 30% cyclohexyl
iodide (12) also isolated from this reaction (cf. Scheme 4).
Scheme 4
(12) The trisubstituted vinyl iodides (Z)-10bI and (Z)-11bI showed 16%
and 10% NOEs, respectively, for the vinyl proton upon irradiation of the
allylic CH2 moiety; the complementary experiment revealed a 10% NOE
in the methine hydrogen of (E)-10bI upon irradiation of the allylic CH2
moiety; a similar conformation experiment was not possible for (E)-11bI
since both allylic methylene and methine were not sufficiently separated in
chemical shift.
of (E)-9aI, which gives a 30% yield of (Z)-11aI with no trace
of the expected isomeric iodide (E)-11aI. Analysis of the
reaction byproducts reveals the presence of cyclohexyl iodide
(12) (50%) accompanied by a 60% yield of a 1:1 mixture of
isomeric styrenes (Z)-13 and (E)-13 (Schemes 3 and 4 and Table
1, entry 3). This observation reveals that the incipient cyclo-
hexyl radicals react with the initially-produced vinyl iodide (E)-
11aI in preference to the substrate vinyl triflone (E)-9aI,
resulting in stereospecific radical deiodination. The aforemen-
tioned result stands in stark contrast to the chemistry of vinyl
triflone (Z)-9aI which is sufficiently reactive so as to render
(13) For a set of recent references describing the value of fluorinated
organics, see: Umemoto, T.; Adachi, K. J. Org. Chem. 1994, 59, 5692.

Stereospecific Alkenylation of C-H Bonds
J. Am. Chem. Soc., Vol. 119, No. 18, 1997 4125
Scheme 6
Scheme 8
Scheme 7
Scheme 9
the preparation of vinyl triflones substituted in the â position
with a fluorine atom. Reaction of phenylethynyl triflone 8a
with HF‚pyridine in acetonitrile stereospecifically produced (Z)-
vinyl fluoride (Z)-9aF in 80% yield. Photochemical equilibra-
tion of (Z)-9aF at 254 nm in acetonitrile at 25 °C for 1.5 h
afforded a ∼1:1 Z/E mixture from which a sample of (E)-9aF
was obtained by silica gel chromatography (Scheme 7). Hy-
drofluorination of n-octynyl triflone 8b was not as simple as
expected; for the first time, a hydrohalogenation reaction had
failed to stereospecifically effect a trans-addition to the acety-
lenic triflone. In this instance a mixture of both (Z)- and (E)-
vinyl triflones (Z)-9bF and (E)-9bF was formed, accompanied
by a significant quantity of the bis addition product 14.
Although the point was not experimentally tested, one can
speculate that difluoride 14 is the progenitor of the unexpected
vinyl triflone (E)-9bF by a pyridine-promoted â-elimination
reaction (Scheme 7). No further effort at optimization of the
synthesis of the alkyl-substituted â-fluorovinyl triflones (Z)-
9bF and (E)-9bF was undertaken as these substrates were found
to be inert to the conditions of the C-H alkenylation reaction.
The alkyl-substituted â-fluorovinyl triflones (Z)-9bF and (E)-
9bF were unreactive with cyclohexane (or THF) even when
heated for extended periods of time (Scheme 8 and Table 1,
entries 17 and 18). The deactivation observed is likely a
consequence of the optimal 2p-π resonance for fluorine which
accompanies carbon in the second row of the periodic table, an
observation which presaged difficulties which lay ahead with
vinyl triflones bearing oxygen and nitrogen substituents. For-
tunately, at least the phenyl-substituted â-fluorovinyl triflones
(Z)-9aF and (E)-9aF were still able to undergo exceptionally
high-yielding reactions with THF and cyclohexane. As ex-
pected, the transformation of (Z)-9aF was essentially stereospe-
cific, affording fluoroolefins (Z)-10aF and (Z)-11aF with 77:1
and >100:1 selectivity, respectively (Scheme 8 and Table 1,
entries 13 and 14). The isomeric â-fluorovinyl triflone (E)-
9aF saw substantially decreased stereoselectivity, providing the
fluoroolefins (E)-10aF and (E)-11aF with 3:1 and 8:1 selectiv-
ity, respectively (Scheme 8 and Table 1, entries 15 and 16).
While the modest selectivity exhibited with â-fluorovinyl
triflone (E)-9aF seems unimpressive compared to the earlier
examples, these results are quite informative when contrasted
with the previously reported reaction of disubstituted â-phe-
nylvinyl triflone (Z)-15 (Scheme 9).2 In this latter instance,
reaction of (Z)-15 with THF afforded an initial adduct which
possessed a sufficient lifetime to enable bond rotation in
preference to elimination of the (trifluoromethyl)sulfonyl radical
(Scheme 9, k1H . k2H), resulting in the exclusive formation of
(E)-16 with no trace of (Z)-16, the product of retained
stereochemistry. Since we know from the fluoro series shown
in Scheme 8 that k-1F < k3F ((E)-9aF gives a 3:1 ratio of (E)-
10aF:(Z)-10aF), this fixes the composite electronic and steric
destabilization of replacing a hydrogen with a fluorine atom on
the incipient â-(trifluoromethyl)sulfonyl radical as being worth
a factor of at least 200 (>70 × 3).
Having established the utility of â-halovinyl triflones in the
C-H alkenylation reaction, we next turned to the synthesis of
vinyl triflones bearing oxygen functionality. Simple base-
catalyzed addition of methanol to acetylenic triflone 8a was
high-yielding but nonstereospecific, affording (Z)-17a and (E)-
17a as a 1:4 mixture.14 Further investigation of the methanol
addition reaction of 8a was not undertaken since attempted
reaction of enol ether (Z)-17a/(E)-17a with THF at reflux for
72 h under the standard radical conditions returned the substrate
unchanged. This observation is reminiscent of vinyl fluorides
(Z)-9bF and (E)-9bF, except that in this case even the presence
of the radical-stabilizing phenyl group was insufficient to
overcome the strong resonance effect of the methoxy moiety
(Scheme 10).
Armed with the hypothesis that substitution of a carboxylate
group for the ether moiety might decrease the lone pair density
on oxygen to a sufficient extent so as to engender alkenylation
reactivity, we examined additions of benzoic acid to acetylenic
triflones 8a,b. Reaction of 8a with benzoic acid in the presence
of a small amount of sodium benzoate in acetonitrile smoothly
afforded trisubstituted enol benzoate (Z)-19a as a single
(14) Hanack reports the addition of ethanol to 8a to give the correspond-
ing ethyl enol ether but does not define the stereochemistry of the process
(Massa, F.; Hanack, M.; Subramanian, L. R. J. Fluorine Chem. 1982, 19,
601).

4126 J. Am. Chem. Soc., Vol. 119, No. 18, 1997
Xiang et al.
Table 2. Formation of â-Carbonates of Trisubstituted Vinyl
Triflones
Scheme 10
yield Z:E
run substrate
conditions
Et3N, -78 °C, 1 h (Z)-22a + (E)-22a
Et3N, 0 °C, 1 h (E)-22a + (E)-22a 86 14:1
Et3N, -78 °C, 1 h (E)-22b + (E)-22b 77 1:11
products
(%) ratio
1
2
3
4
5
20a
20a
20b
20b
20b
85
2:1
Et3N, 0 °C, 1 h
LDA, -78 f 0
°C, 1 h
(E)-22b + (E)-22b 71 1:10
(E)-22b + (E)-22b 70 1:4
Scheme 11
Scheme 12
stereoisomer. While photochemical isomerization of the (Z)-
enol benzoate (Z)-19a in acetonitrile provided a ∼1:1 Z/E
mixture, isolation of (E)-19a by silica gel chromatography was
initially hampered by partial hydrolysis of the desired isomer
(E)-19a to â-keto triflone 20a. The Z isomer (Z)-19a was not
appreciably degraded under these conditions. Fortunately,
chromatography of the 1:1 Z/E photolysis mixture (Z)-19a/(E)-
19a on acetone-deactivated silica gel was effective at affording
a sample of (E)-19a, with only a trace of hydrolysis product
20a being generated. Similar synthesis of alkyl-substituted enol
carboxylate (Z)-19b15 from n-octynyl triflone (8b) required use
of minimal amounts of the basic catalyst in order to avoid
isomerization of the vinyl triflone (Z)-19b to the deconjugated
allyl triflone (E)-21b15 (Scheme 10).
25a,b, and (Z)-26a,b, and (E)-26a,b in excellent yields with
good to outstanding stereocontrol17 (Scheme 12 and Table 3).
Finally, the chemistry of nitrogen-substituted vinyl triflones
was examined. Reaction of 8a with diethylamine provides
â-aminovinyl triflone (E)-27a, the E stereochemistry presumably
a consequence of intramolecular proton transfer from the dipolar
intermediate (Scheme 13). As anticipated, on the basis of the
results from the fluorine and oxygen series, this substrate is
completely unreactive in the C-H functionalization reaction.
Base-catalyzed addition of phthalimide to acetylenic triflones
8a,b stereospecifically affords the â-phthalimidovinyl triflones
(Z)-29a,b. Photoisomerization of (Z)-29a in acetonitrile pro-
vides a sample of the isomeric vinyl triflone (E)-29a. As can
be seen in Table 4, the phenyl-substituted phthalimides (Z)-
29a and (E)-29a provide adducts (Z)-30a, (E)-30a, (Z)-31a, and
As the isolation of (E)-19a was initially problematical, we
also explored the use of enol carbonates as more robust acyloxy
substituents. In this approach, â-keto triflone 20a was inten-
tionally prepared in near-quantitative yield by reaction of 8a
with acetone and water.16 Similar hydrolysis of octynyl triflone
(8b) afforded a 93% yield of keto triflone 20b provided that
dilute (0.003 M) conditions were employed to prevent conjugate
addition of 20b to 8b. Treatment of â-keto triflones 20a,b under
the conditions of Table 2 provided enol carbonates (Z)-22a/
(E)-22a and (Z)-22b/(E)-22b which could be separated by
chromatography on acetone-deactivated silica gel without
hydrolytic difficulties (Scheme 11).
In marked contrast to the failure of (Z)-17a/(E)-17a to
undergo the alkenylation reaction, benzoates (Z)-19a,b and (E)-
19a,b and carbonates (Z)-22a,b and (E)-22a,b smoothly undergo
the C-H alkenylation reaction with THF and cyclohexane to
provide the alkenylated enol benzoates (Z)-23a,b, and (E)-23a,b,
(Z)-24a,b, and (E)-24a,b and enolcarbonates (Z)-25a,b, (E)-
(17) Spectral information and stereochemical assignments are given
below.
(15) The trisubstituted enol carboxylate (Z)-19b showed 15% NOE
enhancement on the vinyl proton upon irradiation of the allylic CH2 moiety.
The allyl triflone (E)-21b showed 5% NOE on the allylic protons when
the CH2 R to the triflone group was irradiated; the same results were obtained
on vinyl proton and methylene protons R to the triflone group when the
allylic CH2 moiety was irradiated.
The trisubstituted enol carbonate (Z)-25b showed a 10% NOE increase of
the vinyl proton when the allylic methylene was irradiated, while (E)-25b
only showed a 10% NOE of the methine proton upon irradiation of the
allylic CH2 moiety. Similar results were obtained from NOE phenyl
irradiation experiments with the trisubstituted enol carbonates (Z)-26a and
(E)-26a.
(16) Compound 20a has been previously prepared by Hanack et. al.,14
who report a 47% yield for recrystallized material, prepared for securing
an analytical sample. We find that the crude â-keto triflone may be routinely
used for all synthetic purposes.

Stereospecific Alkenylation of C-H Bonds
J. Am. Chem. Soc., Vol. 119, No. 18, 1997 4127
Table 3. C-H Alkenylation Reactions of â-Oxygenated Vinyl
with moderate to very high retention of the triflone stereochem-
istry, the 30 examples examined having an average stereospeci-
ficity of 48:1, over a range of 3:1 to 177:1. The most successful
substrates in terms of both yield and stereospecificity were those
with the greatest synthetic potential: vinyl iodides, vinyl
bromides, and vinyl carbonates. Efforts at incorporating the
synthetic potential of this new C-H alkenylation strategy into
the arena of total synthesis are under active investigation.
Triflones
yield Z:E
(%) ratioc
run
substrate
conditionsa
productsb
1
2
3
4
5
6
7
8
9
(Z)-17a/(E)-17a THF, 3 d
(Z)-18a/(E)-18a
(Z)-23a + (E)-23a 91
0
NR
(Z)-19a
(Z)-19a
(E)-19a
(E)-19a
(Z)-22a
(Z)-22a
(E)-22a
(E)-22a
THF, 5 h
c-C6H12, 12 h (Z)-24a + (E)-24a 94
THF, 8 h (Z)-23a + (E)-23a 95
c-C6H12, 1 d (Z)-24a + (E)-24a 93
THF, 4.5 h (Z)-25a + (E)-25a 97
28:1
156:1
1:3
1:33
16:1
Experimental Section
c-C6H12, 12 h (Z)-26a + (E)-26a 95d 49:1
THF, 5 h
c-C6H12, 12 h (Z)-26a + (E)-26a 96d 1:35
THF, 8 d
(Z)-25b + (E)-25b 85d 35:1
c-C6H12, 4 d (Z)-26b + (E)-26b 83d 47:1
THF, 8 d
(Z)-25b + (E)-25b 55d 1:3e
c-C6H12, 4 d (Z)-26b + (E)-26b 77d 1:28
(Z)-25a + (E)-25a 89
1:22
General Methods. Melting points were obtained on a MEL-TEMP
apparatus and are uncorrected. Unless otherwise stated, reactions were
carried out under argon in flame-dried glassware. Tetrahydrofuran
(THF) and diethyl ether (Et2O) were distilled from sodium-benzophe-
none ketyl. Dichloromethane and benzene were distilled from calcium
hydride. Cyclohexane was stored over sodium metal. Deuterated NMR
solvents (CDCl3 and CD3CN) were stored over 4 Å molecular sieves
for several days prior to use. Flash chromatography on silica gel was
carried out as described by Still18 (230-400 mesh silica gel was used).
1H and 13C NMR spectra were obtained using GE QE-300 NMR and
Varian Gemini 200 NMR spectrometers at 300 or 200 MHz and 75 or
50 MHz, respectively. 1H NMR chemical shifts are reported in parts
per million relative to the residual protonated solvent resonance: CHCl3,
δ 7.26; C6D5H, δ 7.15. Splitting patterns are designated as s (singlet),
d (doublet), t (triplet), q (quartet), p (pentet), m (multiplet), br
(broadened). Coupling constants (J) are reported in hertz. 13C NMR
chemical shifts are reported in parts per million relative to solvent
resonance: CDCl3, δ 77.00; C6D6, δ 128.00. Mass spectral data were
obtained on a Finnigan 4000 mass spectrometer (low resolution) and a
CEC 21 110 B high-resolution mass spectrometer, with the molecular
ion designated as M.
10 (Z)-22b
11 (Z)-22b
12 (E)-22b
13 (E)-22b
a AIBN (20 mol %), solvent at reflux. b Product stereochemistry is
assigned by NOE experiments. c Product ratios of >10:1 were assigned
by analytical HPLC. Product ratios of <10:1 were assigned by NMR
integration of the crude reaction mixture. NR ) no reaction. d This
reaction requires 1-3 additional portions of AIBN (0.3 equiv). e This
reaction also produces 30% of the ketone from hydrolysis of enol
carbonate (E)-25b, making the actual Z:E ratio 1:5.
Scheme 13
Representative Experimental Procedures. See Supporting Infor-
mation for the synthesis of the following compounds: (E)-9aF, (Z)-
9bF, (E)-9bF, (E)-10aBr, (Z)-11aBr, (Z)-19b, (E)-21b, (Z)-23a, (E)-
23a, (Z)-24a, (E)-24a, (Z)-25a, (E)-25a, (Z)-25b, (E)-25b, (Z)-26a,
(E)-26a, (Z)-26b, and (E)-26b.
Synthesis of (Z)-2-Bromo-2-phenyl-1-ethenyl Trifluoromethyl
Sulfone ((Z)-9aBr). To a solution of phenylethynyl triflone (8a) (0.303
g, 1.29 mmol) in 10 mL of THF at 0 °C was added lithium bromide
(0.336 g, 3.87 mmol, 3 equiv) followed by trifluoroacetic acid (0.221
g, 1.94 mmol, 1.5 equiv). The addition is complete after stirring at
room temperature for 4 h (as determined by TLC: SiO2, 0.05:1 EtOAc/
hexane). The THF was removed in Vacuo, and the residue was
partitioned between ether and water. The organic layer was dried (Na2-
SO4), filtered, and concentrated. The resulting oil was purified by
column chromatography (silica gel, 5% EtOAc/hexane) to afford 0.358
g (88%) of (Z)-9aBr as a yellow solid (Rf 0.25, SiO2, 0.05:1 EtOAc/
hexane): mp 46-48 °C; 1H NMR (200 MHz, CDCl3) δ 7.14 (s, 1H),
Table 4. C-H Alkenylation Reactions of â-Aminated Vinyl
Triflones
yield
(%)
Z:E
run substrate
conditionsa
(E)-27a THF, 3 d
(Z)-29a THF, 6 h
(Z)-29a c-C6H12, DCE,d 3 d (Z)-31a + (E)-31a
(E)-29a THF, 6 h (Z)-30a + (E)-30a
(E)-29a c-C6H12, DCE,d 3 d (Z)-31a + (E)-31a
productsb
(E)-28a
(Z)-30a + (E)-30a
ratioc
7.47-7.72 (m, 5H); 13C NMR (75 MHz, CDCl3) δ 119.74 (q, JC,F
)
1
2
3
4
5
6
7
0
NR
326 Hz), 120.48, 128.61, 129.25, 133.06, 137.09, 149.12; mass spectrum
(CI) m/z 315 (M + H+, base peak); HRMS m/z calcd for C9H6BrF3O2S
313.9224, found 313.9217.
95 >100:1
82 >100:1
89 1:25
81 1:10
0
0
Synthesis of (E)-2-Bromo-2-phenyl-1-ethenyl Trifluoromethyl
Sulfone ((E)-9aBr). Acetonitrile was purged with argon for 15 min.
before use. Vinyl bromide (Z)-9aBr (0.302 g, 0.96 mmol) was
dissolved in acetonitrile (24 mL) and placed in a quartz tube under
argon. The reaction mixture was irradiated with 254 nm ultraviolet
light in a Rayonet reactor for 1 h. The mixture was then partitioned
between ether and water. Normal workup and column chromatography
(silica gel, 5% CH2Cl2/hexane) afforded 0.139 g (46%) of (E)-9aBr
as a yellow solid (Rf 0.40, SiO2, 0.05:1 EtOAc/hexane) in addition to
46% recovered (Z)-9aBr. Data for (E)-9aBr: mp 81-83 °C; 1H NMR
(300 MHz, CDCl3) δ 7.05 (s, 1H), 7.45 (m, 5H); 13C NMR (75 MHz,
CDCl3) δ 119.50 (q, JC,F ) 326 Hz), 122.30, 128.27, 128.44, 131.69,
135.29, 151.00; mass spectrum (CI) m/z 315 (M + H+, base peak);
HRMS m/z calcd for C9H7BrF3O2S 314.9224, found 314.9225.
Synthesis of (Z)-2-Fluoro-2-phenyl-1-ethenyl Trifluoromethyl
Sulfone ((Z)-9aF). Phenylethynyl triflone (8a) (40 mg, 0.17 mmol)
dissolved in acetonitrile (1 mL) in a polyethylene vial was cooled to 0
(Z)-29b THF, 120 °C, 1 d
(Z)-29b c-C6H12, 3 d
(Z)-30b + (E)-30b
(Z)-31b + (E)-31b
NR
NR
a AIBN (20 mol %), solvent at reflux, except for run 6, which used
a sealed tube. b Product stereochemistry is assigned by NOE experi-
ments (see supplemental material). c Product ratios were assigned by
reversed phase analytical HPLC. NR ) no reaction. d This reaction
requires addition of four additional portions of AIBN (0.3 equiv). This
reaction was run in 1,2-dichloroethane as solvent because (Z)-29a and
(E)-29a were insoluble in cyclohexane or acetonitrile.
(E)-31a with excellent stereocontrol, while surprisingly, the
alkyl-substituted phthalimide (Z)-29b is unreactive under the
standard conditions (Scheme 13).
In conclusion, it has been established that â-heteroatom-
functionalized trisubstituted vinyl triflones undergo trifluoro-
methyl radical-promoted C-H alkenylation reactions with two
test substrates, THF and cyclohexane. The reactions proceed
(18) Still, W. C.; Kahn, M.;Mitra, A. J. Org. Chem. 1978, 43, 923.

4128 J. Am. Chem. Soc., Vol. 119, No. 18, 1997
Xiang et al.
°C. HF-pyridine (3 mL) was added, and the mixture was stirred at 0
°C for 30 min. The reaction mixture was diluted with chloroform (50
mL) and washed with water and brine. The organic layer was dried
(Na2SO4), filtered, and concentrated. The resulting oil was purified
by column chromatography (silica gel, 5% EtOAc/hexane) to afford
35 mg (80%) of (Z)-9aF as a light yellow solid (mp 75-77 °C) Note:
More reproducible results were obtained by dilution of HF-pyridine
(3 mL) with pyridine (2 mL): 1H NMR (200 MHz, CDCl3) δ 6.36 (d,
JF,H ) 29.6 Hz, 1H), 7.68 (m, 5H); 13C NMR (50 MHz, CDCl3) δ
98.37 (d, JF,C ) 10.9 Hz), 120.16 (q, JF,C ) 324.0 Hz), 127.44 (d, JF,C
) 8.5 Hz), 127.93 (d, JF,C ) 24.5 Hz), 129.94, 134.96, 172.21 (d, JF,C
) 287.0 Hz); mass spectrum (CI) m/z 255 (M + H+, base peak); HRMS
m/z calcd for C9H6F4O2S 254.0025, found 254.0033.
Synthesis of (Z)-1-Bromo-2-(2-oxolanyl)-1-phenyl-1-ethene ((Z)-
10aBr). To vinyl triflone (Z)-9aBr (0.104 g, 0.33 mmol) in 8 mL of
dry THF was added AIBN (11 mg, 0.07 mmol, 0.2 equiv) under argon.
The reaction mixture was heated to reflux. The reaction was complete
within 5 h. After the mixture was cooled to room temperature, THF
was removed in Vacuo, and the residue was partitioned between ether
and water. The organic layer was dried (Na2SO4), filtered, and
concentrated. The resulting oil was purified by column chromatography
(silica gel, 5% EtOAc/hexane) to afford 75 mg (90%) of (Z)-9aBr as
a colorless oil (Rf 0.25, SiO2, 0.05:1 EtOAc/hexane): 1HNMR (300
MHz, CDCl3) δ 1.70-2.32 (m, 4H), 3.92 (m, 2H), 4.81 (q, J ) 7.1
Hz, 1H), 6.35 (d, J ) 7.0 Hz, 1H), 7.30-7.57 (m, 5H); 13C NMR (75
MHz, CDCl3) δ 26.16, 31.85, 68.47, 79.52, 125.54, 127.66, 128.37,
128.86, 132.96, 139.31; mass spectrum (CI) m/z 173 (M + H+ - HBr,
1.00), 253 (M + H+, 0.47); HRMS m/z calcd for C12H13BrO 252.0150,
found 252.0147.
Synthesis of (Z)-1-Iodo-2-(2-oxolanyl)-1-phenyl-1-ethene ((Z)-
10aI). To vinyl triflone (Z)-9aI (45 mg, 0.12 mmol) in 5 mL of dry
THF was added AIBN (3 mg, 0.15 equiv) under argon at room
temperature. The reaction mixture was heated at reflux for 12 h. The
mixture was cooled to 25 °C, THF was removed in Vacuo, and the
residue was partitioned between ether and water. The organic layer
was dried (Na2SO4), filtered, and concentrated. The resulting oil was
purified by column chromatography (silica gel, 5% EtOAc/hexane) to
afford 34 mg (91%) of (Z)-10aI as a colorless oil: 1H NMR (200 MHz,
CDCl3) δ 1.70 (m, 1H), 2.02 (m,1H), 2.33 (m, 1H), 3.91 (m, 1H), 4.63
(q, J ) 7.0 Hz, 1H), 6.09 (d, J ) 7.0 Hz, 1H), 7.40 (m, 1H); 13C NMR
(50 MHz, CDCl3) δ 26.56, 32.08, 69.06, 84.46, 104.65, 128.70, 129.02,
140.00, 142.96; mass spectrum (CI) m/z 301 (M + H+, base peak);
HRMS m/z calcd for C12H13IO 300.0011, found 300.0014.
peak), 357(M + H+, 0.04); HRMS m/z calcd for C16H11F3O4S 357.0408,
found 357.0397.
Synthesis of 1-Phenyl-2-[(trifluoromethyl)sulfonyl]-1-ethanone
(20a) and 1-[(Trifluoromethyl)sulfonyl]-2-octanone (20b). Phenyl-
ethynyl triflone (8a) or n-octynyl triflone (8b) (0.30 mmol) was
dissolved in 100 mL of 1:1 acetone/water and stirred at 25 °C for 2
days followed by removal of the acetone in Vacuo. The residue was
extracted with ether, washed with brine, dried (MgSO4), filtered, and
concentrated. The resulting oil (20a)16 or white solid (20b) was purified
by column chromatography (silica gel, 8% EtOAc/hexane) to afford a
98% yield of 20a (colorless oil in our hands, but known to be a 36-
37 °C mp solid16) or 93% yield of 20b (mp 68-69 °C).
Data for 20a: 1H NMR (200 MHz, CDCl3) δ 4.87 (s, 2H), 7.50-
7.80 (m, 3H), 7.90-8.05 (m, 2H); 13C NMR (50 MHz, CDCl3) δ 57.3,
1
119.7 (q, JC,F ) 328 Hz), 129.7, 135.5, 135.8, 185.0; mass spectrum
(EI) m/z 105 (PhCO+, base peak), 183 (M+ - CF3, 0.10), 252 (M+,
0.15); mass spectrum (CI) m/z 253 (M + H+, base peak); HRMS m/z
calcd for C9H7F3O3S 252.0068, found 252.0065.
3
Data for 20b: 1H NMR (200 MHz, CDCl3), δ 0.89 (t, JH,H ) 6.5
3
Hz, 3H), 1.20-1.40 (m, 6H), 1.50-1.75 (m, 2H), 2.74 (t, JH,H ) 5.6
Hz, 2H), 4.25 (s, 2H); 13C NMR (50 MHz, CDCl3) δ 14.4, 22.9, 23.5,
28.8, 31.9, 45.1, 60.3, 119.5 (q, 1JC,F ) 327 Hz), 194.9; mass spectrum
(CI) m/z 261 (M + H+, base peak); HRMS m/z calcd for C9H15F3O3S
261.0772, found 261.0766.
Synthesis of Trisubstituted Vinyl Triflone Carbonates (Z)-22a
and (E)-22a or (Z)-22b and (E)-22b. â-Keto triflone 20a or 20b (0.30
mmol) was dissolved in THF (10 mL) and cooled to -78 °C (or 0 °C
in order to get different Z/E product ratios). A 1.1 equiv sample of
triethylamine was added, and the mixture was stirred at -78 °C (or 0
°C) for 10-15 min followed by addition of 1.1 equiv of ethyl
chloroformate, which produced a white precipitate. The reaction
mixture was stirred for 1 h, warmed to 0 °C, and filtered through
acetone-deactivated silica gel, followed by concentration of the filtrate.
The resulting oil was purified and separated by column chromatography
(acetone-deactivated silica gel, 0-3% EtOAc/hexane) to afford 70-
86% yield of (Z)-22a and (E)-22a or (Z)-22b and (E)-22b (all
compounds were colorless oils).
Data for [(E)-1-phenyl-2-[(trifluoromethyl)sulfonyl]-1-ethenyl]car-
bonic acid ethyl ester ((Z)-22a): 1H NMR (200 MHz, CDCl3) δ 1.37
3
3
(t, JH,H ) 7.1 Hz, 3H), 4.33 (q, JH,H ) 7.1 Hz, 2H), 6.51 (s, 1H),
7.43-7.70 (m, 5H); 13C NMR (50 MHz, CDCl3) δ 14.5, 67.0, 107.6,
3
120.1 (q, JC,F ) 326 Hz), 127.4, 128.8, 130.0, 131.6, 134.0, 151.1,
165.3; mass spectrum (CI) m/z 253 (M + H+ - CO2C2H4, base peak),
325 (M + H+, 0.80); HRMS m/z calcd for C12H11F3O5S 325.0358, found
325.0351.
Synthesis of 1-[(Z)-1-[(Phenylcarbonyl)oxy]-2-[(trifluoromethyl)-
sulfonyl]-1-ethenyl]benzene ((Z)-19a). Phenylethynyl triflone (8a) (50
mg, 0.21 mmol) was dissolved in acetonitrile (5 mL) at 25 °C. Two
equivalents of benzoic acid and 0.1 equiv of sodium benzoate were
added, and the mixture was stirred at 25 °C for 5 h. The reaction
mixture was concentrated in Vacuo, washed with saturated sodium
bicarbonate solution, and extracted with ether. The extract was washed
with brine, dried (MgSO4), filtered, and concentrated. The resulting
white solid was purified by column chromatography (silica gel, 8%
EtOAc/hexane) to afford 71 mg (97%) of (Z)-19a mp 120-121 °C;
Data for [(E)-1-phenyl-2-[(trifluoromethyl)sulfonyl]-1-ethenyl]car-
bonic acid ethyl ester ((E)-22a): 1H NMR (200 MHz, CDCl3) δ 1.32
3
3
(t, JH,H ) 7.1 Hz, 3H), 4.27 (q, JH,H ) 7.1 Hz, 2H), 6.69 (s, 1H),
7.40-7.60 (m,5H); 13C NMR (50 MHz, CDCl3) δ 14.4, 66.8, 109.5,
1
120.0 (q, JC,F ) 326 Hz), 128.6, 130.0, 130.2, 132.7, 150.9, 168.0;
mass spectrum (CI) m/z 253 (M + H+ - CO2C2H4, 0.68), 325 (M +
H+, base peak); HRMS m/z calcd for C12H11F3O5S 325.0358, found
325.0351.
1H NMR (200 MHz, CDCl3) δ 6.66 (s, 1H), 7.45-7.80 (m, 8H), 8.15-
Data for [(Z)-1-hexyl-2-[(trifluoromethyl)sulfonyl]-1-ethenyl]car-
1
8.30 (m, 2H); 13C NMR (50 MHz, CDCl3) δ 107.8, 120.3 (q, JC,F
)
bonic acid ethyl ester (Z)-22b): 1H NMR (200 MHz, CDCl3) δ 0.88
3
3
326 Hz), 127.4, 127.9, 128.9, 129.5, 130.0,131.2, 131.9, 133.9, 135.1,
163.6, 167.2; mass spectrum (EI) m/z 105 (PhCO+, base peak), 287
(M+ - CF3, 0.06); mass spectrum (CI) m/z 105 (PhCO+, base peak),
357 (M + H+, 0.07); HRMS m/z calcd for C16H11F3O4S 357.0408, found
357.0400.
(t, JH,H ) 6.5 Hz, 3H), 1.22-1.40 (m, 6H), 1.38 (t, JH,H ) 7.1 Hz,
3H), 1.50-1.70 (m,2H), 2.54 (t, 3JH,H ) 7.5 Hz, 2H), 4.33 (q, 3JH,H
)
7.1 Hz, 2H), 6.00 (s, 1H); 13C NMR (50 MHz, CDCl3) δ 14.4, 14.5,
1
22.9, 26.1 28.8, 31.7, 35.8, 66.7, 109.3, 120.0 (q, JC,F ) 326 Hz),
150.8, 172.2; mass spectrum (CI) m/z 333 (M + H+, base peak); HRMS
m/z calcd for C12H19F3O5S 333.0984, found 333.0990.
Synthesis of 1-[(E)-1-[(Phenylcarbonyl)oxy]-2-[(trifluoromethyl)-
sulfonyl]-1-ethenyl]benzene ((E)-19a). (Z)-19a (71 mg) dissolved in
acetonitrile (50 mL) was irradiated with 254 nm ultraviolet light in a
Rayonet reactor (internal temperature 35 °C) for 5.5 h. The reaction
mixture was concentrated and separated by column chromatography
(acetone-deactivated silica gel, 0-3% EtOAc/hexane) to afford 61 mg
(85%) of a mixture of (Z)-19a (33 mg) and (E)-19a as a colorless oil
(28 mg): 1H NMR (200 MHz, CDCl3) δ 6.77 (s, 1H), 7.40-7.75 (m,
8H), 8.05-8.15 (m, 2H); 13C NMR (50 MHz, CDCl3) δ 110.7, 120.1
Data for [(E)-1-hexyl-2-[(trifluoromethyl)sulfonyl]-1-ethenyl]car-
bonic acid ethyl ester ((E)-22b): 1H NMR (200 MHz, CDCl3) δ 0.88
3
3
(t, JH,H ) 6.5 Hz, 3H), 1.23-1.45 (m, 6H), 1.39 (t, JH,H ) 7.1 Hz,
3H), 1.52-1.70 (m,2H), 2.80 (t, 3JH,H ) 7.6 Hz, 2H), 4.33 (q, 3JH,H
)
7.1 Hz, 2H), 6.62 (s, 1H); 13C NMR (50 MHz, CDCl3) δ 14.5, 22.8,
1
27.7, 29.2, 31.7, 31.8, 66.6, 107.8, 120.0 (q, JC,F ) 326 Hz), 150.8,
173.9; mass spectrum (CI) m/z 333 (M + H+, base peak); HRMS m/z
calcd for C12H19F3O5S 333.0984, found 333.0977.
1
(q, JC,F ) 326 Hz), 127.7, 128.1, 128.6, 129.5, 129.9, 130.9, 132.6,
C-H Alkenylation Reactions of â-Oxygenated Vinyl Triflones
(Z)-22a,b and (E)-22a,b. â-oxygenated trisubstituted vinyl triflones
(0.20 mmol) were dissolved in THF or cyclohexane (10 mL), and 0.2
135.3, 163.4, 168.5; mass spectrum (EI) m/z 105 (PhCO+, base peak),
223 (M+ - SO2CF3, 0.04);mass spectrum (CI) m/z 105 (PhCO+,base

Stereospecific Alkenylation of C-H Bonds
J. Am. Chem. Soc., Vol. 119, No. 18, 1997 4129
1
equiv of AIBN was added (when reaction times were longer than one
day, additional portions of AIBN were periodically added as required).
The reactions of Table 3 were conducted at reflux for 12 h to 8 days.
The reaction mixtures were concentrated, and the resulting oil was
purified by column chromatography (silica gel, 5% EtOAc/hexane) to
afford the products in the yields indicated in Table 3. See the
Supporting Information section for the spectra of the products (Z)-
23-26a,b and (E)-23-26a,b.
(Z)-30a as a white solid: mp 110-125 °C dec; H NMR (300 MHz,
CDCl3) δ 1.45 (m, 2H), 1.80 (m, 2H), 3.40 (m, 1H), 3.57 (m, 1H),
4.50 (q, J ) 7.39 Hz, 1H), 6.41 (d, J ) 7.79 Hz, 1H), 6.88 (m, 5H),
7.43 (m, 4H); 13C NMR (75 MHz, CDCl3) δ 26.10, 32.73, 67.22, 76.04,
124.01, 124.39, 125.86, 129.14, 130.95, 132.45, 133.23, 134.89, 136.33,
168.01; mass spectrum (CI) m/z 320 (M + H+, base peak); HRMS m/z
calcd for C20H17O3N 319.1208, found 319.1201.
Synthesis of 2-[(Z)-1-Phenyl-2-[(trifluoromethyl)sulfonyl]-1-ethe-
nyl]-2,3-dihydro-1H-benz[c]azole-1,3-dione ((Z)-29a). To a solution
of phenylethynyl triflone (8a) (1.0 g, 4.3 mmol) in acetonitrile (30 mL)
was added phthalimide (0.63 g, 4.3 mmol) followed by a catalytic
amount of potassium hydroxide. The reaction was complete within 1
h. Acetonitrile was removed by rotary evaporator. The residue was
purified by column chromatography (silica gel, eluted with 2:1 hexane/
ethyl acetate) to afford 1.6 g (99%) of (Z)-29a as white crystals: mp
Acknowledgment. We thank the National Institutes of
Health (Grant GM 32693) and the NSF (Grant CHE 9626837)
for support of this work. Arlene Rothwell provided the MS
data. Special thanks are due to Dr. Douglas Lantrip for
assistance with HPLC analysis and manuscript editing. The
groups of Professors Brown, Negishi, and Andrus are thanked
for access to gas chromatography equipment.
1
118-120 °C; H NMR (300 MHz, CDCl3) δ 6.92 (s, 1H), 7.51 (m,
5H), 7.88 (m, 4H); 13C NMR (75 MHz, CDCl3) δ 115.54, 119.65 (q,
JC,F ) 326 Hz), 124.71, 127.56, 129.55, 129.67, 131.72, 132.92, 133.39,
135.21, 150.25, 165.63; mass spectrum (CI) m/z 382 (M + H+, base
peak); HRMS m/z calcd for C17H11F3NO4S 382.0361, found 382.0353.
Synthesis of 2-[(Z)-2-(2-Oxolanyl)-1-phenyl-1-ethenyl]-2,3-dihy-
dro-1H-benz[c]azole-1,3-dione ((Z)-30a). A solution of (Z)-29a (40
mg, 0.105 mmol) and AIBN (1.7 mg, 0.021 mmol) in THF (2 mL)
was heated to reflux for 10 h. THF was removed on a rotary evaporator.
The resulting residue was purified by column chromatography (silica
gel, eluted with 2:1 hexane/ethyl acetate) to afford 33.1 mg (99%) of
Supporting Information Available: Experimental proce-
dures for the synthesis of (E)-9aF, (Z)-9bF, (E)-9bF, (E)-
10aBr, (Z)-11aBr, (Z)-19b, (E)-21b, (Z)-23a, (E)-23a, (Z)-
24a, (E)-24a, (Z)-25a, (E)-25a, (Z)-25b, (E)-25b, (Z)-26a, (E)-
1
26a, (Z)-26b, and (E)-26b, as well as H and 13C NMR of all
new compounds (118 pages). See any current masthead page
for ordering and Internet access instructions.
JA963636S