Conjugate additions, aza-cope, and dissociative rearrangements and unexpected electrocyclic ring closures in the reactions of 2-(2-Pyrrolidinyl)- substituted heteroaromatic systems with acetylenic sulfones

Article abstract of DOI:10.1021/jo101030b

(Figure presented) The reactions of 2-heteroaryl-substituted pyrrolidines with acetylenic sulfones proceeded via two pathways. The first involves conjugate addition of the pyrrolidine to the acetylenic sulfone to afford a zwitterion, followed by dissociation of the C-N bond and recombination of the resulting carbocation and vinyl anion to afford the corresponding azepine derivative. The second comprises a cascade of conjugate addition, aza-Cope rearrangement and anionic 6π electrocyclic ring-closure steps. The stability of the carbocation intermediate formed by C-N cleavage determines the dominant pathway.

Full text of DOI:10.1021/jo101030b

pubs.acs.org/joc
Cope rearrangements of the resulting zwitterions 2.5,6 Be-
Conjugate Additions, Aza-Cope, and Dissociative
Rearrangements and Unexpected Electrocyclic Ring
Closures in the Reactions of 2-(2-Pyrrolidinyl)-
Substituted Heteroaromatic Systems with
Acetylenic Sulfones
cause the rearrangement step is accompanied by the cancel-
lation of charge in the zwitterion, these reactions proved
exceptionally facile and proceeded at temperatures between
-78 and 40 °C. When cyclic R-vinyl amines were used, the
overall process resulted in ring-expansion of the original
amine by four carbon atoms to afford products 3, containing
rings ranging in size from 9 to 17 members (Scheme 1).5 An
extension to the ring-expansion of R-vinyl azetidines was
subsequently reported by Couty et al.,7 while an iterative
variation of this process was used in the synthesis of the
macrocyclic amines motuporamine A and B in our labo-
ratory.5b Several related studies of the reactions of tertiary
allyl amines with DMAD and other acetylenic esters have
also been reported.8
Mitchell H. Weston, Masood Parvez, and Thomas G. Back*
Department of Chemistry, University of Calgary, Calgary,
AB, Canada, T2N 1N4
tgback@ucalgary.ca
Received May 26, 2010
Two examples of anomalous behavior were observed
during our previous investigation.5b In the first, the zwitterion
derived from an R-vinyl aziridine underwent ring-opening of
the strained aziridinium ion by methanol instead of the usual
aza-Cope rearrangement (Scheme 2). In the second, a dis-
sociative mechanism predominated, wherein a methoxy-
stabilized allyl carbocation was formed by C-N bond cleav-
age (Scheme 3). In contrast, Hassner et al. reported that vinyl
aziridines undergo rearrangements with ring-expansion when
reacted with various other activated acetylenes and alkenes,9
2k
while Lindstrom and Somfai observed [3,3]-aza-Claisen
€
enolate rearrangements of amides of vinyl aziridines. Previous
examples of C-N bond cleavage that followed the initial
The reactions of 2-heteroaryl-substituted pyrrolidines
with acetylenic sulfones proceeded via two pathways.
The first involves conjugate addition of the pyrrolidine
to the acetylenic sulfone to afford a zwitterion, followed
by dissociation of the C-N bond and recombination of
the resulting carbocation and vinyl anion to afford the
corresponding azepine derivative. The second comprises
a cascade of conjugate addition, aza-Cope rearrangement
and anionic 6π electrocyclic ring-closure steps. The sta-
bility of the carbocation intermediate formed by C-N
cleavage determines the dominant pathway.
(2) For recent examples, see: (a) Waetzig, S. R.; Tunge, J. A. J. Am. Chem.
Soc. 2007, 129, 4138–4139. (b) Craig, D.; King, N. P.; Mountford, D. M.
Chem. Commun. 2007, 1077–1079. (c) Hemming, K.; O’Gorman, P. A.; Page,
M. I. Tetrahedron Lett. 2006, 47, 425–428. (d) Fiedler, D.; van Halbeek, H.;
Bergman, R. G.; Raymond, K. N. J. Am. Chem. Soc. 2006, 128, 10240–
10252. (e) Fiedler, D.; Bergman, R. G.; Raymond, K. N. Angew. Chem., Int.
Ed. 2004, 43, 6748–6751. (f) Zheng, J.-F.; Jin, L.-R.; Huang, P.-Q. Org. Lett.
2004, 6, 1139–1142. (g) Davies, S. G.; Garner, A. C.; Nicholson, R. L.;
Osborne, J.; Savory, E. D.; Smith, A. D. Chem. Commun. 2003, 2134–2135.
(h) Winter, R. F.; Rauhut, G. Chem.;Eur. J. 2002, 8, 641–649. (i) Gomes,
ꢀ
M. J. S.; Sharma, L.; Prabhakar, S.; Lobo, A. M.; Gloria, P. M. C. Chem.
Commun. 2002, 746–747. (j) Cardoso, A. S.; Lobo, A. M.; Prabhakar, S.
€
Tetrahedron Lett. 2000, 41, 3611–3613. (k) Lindstrom, U. M.; Somfai, P.
Chem.;Eur. J. 2001, 7, 94–98. (l) McComsey, D. F.; Maryanoff, B. E.
J. Org. Chem. 2000, 65, 4938–4943. (m) Suh, Y.-G.; Kim, S.-A.; Jung, J.-K.;
Shin, D.-Y.; Min, K.-H.; Koo, B.-A.; Kim, H.-S. Angew. Chem., Int. Ed.
1999, 38, 3545–3547. (n) For a related example of a 1-aza-Cope rearrange-
ment (formally the reverse of a 3-aza-Cope process), see: Kang, J.; Kim,
T. H.; Yew, K. H.; Lee, W. K. Tetrahedron: Asymmetry 2003, 14, 415–418.
(3) Walters, M. A. J. Org. Chem. 1996, 61, 978-983 and refs cited therein.
(4) For reviews of acetylenic sulfones, see: (a) Back, T. G. Tetrahedron
2001, 57, 5263–5301. (b) Back, T. G.; Clary, K. N.; Gao, D. Chem. Rev. 2010,
DOI: 10.1021/cr1000546.
(5) (a) Weston, M. H.; Nakajima, K.; Parvez, M.; Back, T. G. Chem.
Commun. 2006, 3903–3905. (b) Weston, M. H.; Nakajima, K.; Back, T. G.
J. Org. Chem. 2008, 73, 4630–4637.
(6) Although we refer to these processes as formal 3-aza-Cope rearrange-
ments, it is possible that they proceed via intramolecular SN0 displacements of
the quaternary nitrogen by the sulfone-stabilized vinyl anion in the zwitterion
intermediates.
The 3-aza-Cope rearrangement provides a potentially
useful method for the conversion of N-allyl-substituted
enamines to the corresponding imines.1,2 A limitation of
such processes is their typically high activation energies,
which result in the requirement for strongly elevated tem-
peratures. Fortunately, quaternization of the amino group
lowers the activation energy substantially and enhances the
synthetic value of the reaction. This may be achieved by
N-alkylation, protonation, or coordination of the nitrogen
atom with Lewis acids.3
We recently demonstrated that a variety of tertiary cyclic
R-vinyl amines or acyclic allyl amines undergo conjugate
additions to acetylenic sulfones 1,4 followed by formal aza-
ꢀ
(7) Drouillat, B.; Couty, F.; Razafimahaleo, V. Synlett 2009, 3182–3186.
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5402 J. Org. Chem. 2010, 75, 5402–5405
Published on Web 07/08/2010
DOI: 10.1021/jo101030b
r
2010 American Chemical Society

Weston et al.
JOCNote
SCHEME 1
TABLE 1. Reactions of 2-(2-N-Benzylpyrrolidyl)-Substituted
Heteroaromatic Compounds with Acetylenic Sulfone 1a
SCHEME 2
SCHEME 3
of these processes further. We now report that the reaction of
1-benzyl-2-(1-benzylpyrrolidin-2-yl)-1H-indole (4) with (p-
toluenesulfonyl)ethyne (1a) proceeded smoothly at room
temperature in acetonitrile, affording the tetrahydroazepine
8 in 90% yield, instead of the aza-Cope product 7. This is
consistent with the expected conjugate addition of 4 to 1a,
followed by dissociation of the C-N bond in the resulting
zwitterion 5, to produce the resonance-stabilized cation 6.
Recombination of the cation with the sulfone-stabilized
vinyl anion then afforded the azepine 8 instead of the
corresponding tetrahydroazonine 7, the expected product
of a formal aza-Cope rearrangement (Scheme 4 and entry 1
of Table 1). The formation of 8 instead of 7 is attributed to
the relatively high stability of the carbocation 6 and the
partial loss of aromaticity of the indole moiety in the forma-
tion of 7. The reactions of acetylenic sulfone 1a with the
corresponding furan, benzofuran, thiophene, and benzo-
thiophene derivatives 9, 11, 13, and 15, respectively, were
performed under similar conditions, affording the analogous
tetrahydroazepine products 10, 12, 14, and 16, respectively,
in generally high yield (Table 1, entries 2-5). The structure of
the furan derivative 10 was established conclusively by 2D
NMR methods, including COSY, HSQC, and HMBC, while
that of 8 was confirmed by X-ray diffraction (see Supporting
Information).
To our surprise, when the indole N-benzyl group of 4 was
replaced with the electron-withdrawing benzenesulfonyl
substituent and the reaction of the resulting indole derivative
17 with 1a was repeated under the same conditions, a
completely different product 22 was isolated in 95% yield
(Scheme 5). The indicated tetracyclic structure and stereo-
chemistry of 22 were confirmed by X-ray diffraction (see
Supporting Information). The analogous tetracyclic product
23 was obtained similarly, albeit in lower yield, when the
pyrrolidine N-benzyl group was replaced with an N-methyl
substituent in 18. Thus, a complete change in reaction path-
way was effected by simply switching the indole N-benzyl
SCHEME 4
conjugate addition of thebaine derivatives to an allenic sulfone
were reported by Kanematsu et al.,10 while other examples of
dissociation during the reactions of allyl amines with variously
activated acetylenes were noted by Schwan and Warkentin,8b
Vedejs and Gingras,8d and by Voskressensky et al.11
We were also interested in investigating the reactions of
acetylenic sulfones with tertiary amines containing R-vinyl
groups that are part of aromatic systems to extend the scope
(10) Fujii, I.; Ryu, K.; Hayakawa, K.; Kanematsu, K. J. Chem. Soc.,
Chem. Commun. 1984, 844–845.
(11) (a) Voskressensky, L. G.; Borisova, T. N.; Listratova, A. V.; Kulikova,
L. N.; Titov, A. A.; Varlamov, A. V. Tetrahedron Lett. 2006, 47, 4585–4589. (b)
Voskressensky, L. G.; Listratova, A. V.; Borisova, T. N.; Alexandrov, G. G.;
Varlamov, A. V. Eur. J. Org. Chem. 2007, 6106–6117. (c) Voskressensky, L. G.;
Listratova, A. V.; Borisova, T. N.; Kovaleva, S. A.; Borisov, R. S.; Varlamov,
A. V. Tetrahedron 2008, 64, 10443–10452.
J. Org. Chem. Vol. 75, No. 15, 2010 5403

Weston et al.
JOCNote
SCHEME 5
SCHEME 6
except 17 and 18, reacted with acetylenic sulfones 1 via the
conjugate addition-dissociation-recombination pathway
shown for 4 in Scheme 4.
The remarkable dichotomy of behavior between
N-(benzenesulfonyl)indoles 17 and 18 and the other com-
pounds studied can be explained on the basis of the relative
stabilities of the carbocation moiety of 6, produced by C-N
bond cleavage in the dissociation pathway. The carbocation
intermediate required for the dissociation mechanism in the
case of 17 and 18 is destabilized by the N-benzenesulfonyl
group, relative to the cations postulated in the reactions of
the otherwise similar N-benzylindole derivative 4 (Scheme 4),
and in the other reactions summarized in Table 1. This sup-
presses the rate of the dissociative mechanism and enables the
aza-Cope pathway to dominate. On the other hand, in the case
of aminal 24, mesomeric electron donation from the extra
nitrogen atom to the corresponding carbocation compensates
for the destabilization of the cation by the N-benzenesulfonyl
group. Thus, the dissociative pathway prevails. The difference
in behavior between N-(benzenesulfonyl)indole 17 and the
analogous pyrrole derivative 26 is more puzzling, but it is worth
noting that electrophilic reactions of indoles occur preferen-
tially at the 3-position, while those of pyrroles generally occur at
C-2. This is consistent with better stabilization of a carbocation
center attached at the 2-position of an adjacent pyrrole ring
than at the same position of an indole moiety. The higher
stability of the corresponding cation would then account for the
greater propensity for the dissociative pathway in pyrrole 26
than in indole 17, despite the presence of the electron-
withdrawing benzenesulfonyl substituent in both compounds.
In conclusion, we have now observed four distinct path-
ways in the reactions of tertiary amines containing R-vinyl or
R-heteroaryl groups with acetylenic sulfones. These all ori-
ginate from the initial conjugate addition of the amine to the
acetylenic sulfone, followed by either the aza-Cope rearran-
gement and ring-expansion in Scheme 1, the aziridine ring-
opening of Scheme 2, the dissociative mechanism resulting in
cleavage of the C-N bond followed by either carbocation
capture with methanol or recombination, as shown in
Schemes 3 and 4, respectively, and the unexpected aza-Cope
rearrangement and electrocyclic ring-closure depicted in
Scheme 5.
group for the more electron-withdrawing sulfonyl substi-
tuent.
We propose that the unexpected formation of the tetra-
cyclic structures 22 and 23 from 17 and 18, respectively, in
Scheme 5 occurs via a cascade of three separate reactions,
where the usual conjugate additions produce the expected
zwitterions 19, which then undergo aza-Cope rearrange-
ments to afford tetrahydroazonines 20, as observed earlier
with the R-vinylamines shown in Scheme 1. This is followed
by a further cyclization to afford the observed products 22
and 23. The possibility that the latter proceeds via a trans-
annular conjugate addition of the indole enamine moiety of
20 to the β-position of the vinyl sulfone group is unlikely
because of the diminished nucleophilicity of the enamine
caused by the electron-withdrawing N-benzenesulfonyl sub-
stituent. A more plausible mechanism is shown in Scheme 5
and is based on the relatively high acidity of the C-3 proton of
the indole moiety of 20, which permits facile deprotonation,
followed by an anionic 6π-electron electrocyclic ring closure
of anions 21, leading to 22 and 23 after reprotonation.12 The
disrotatory nature of the ground state electrocyclic reaction
is consistent with the cis-fused cyclopentene and piperidine
rings found in the final products. The pyrrolidine or piper-
idine moieties of the starting material and product, respec-
tively, presumably serve as the required base in the deproto-
nation step.
In contrast to the above cascade of conjugate addition,
aza-Cope rearrangement and electrocyclic ring-closure steps
observed with 17 and 18, replacement of the pyrrolidine
moiety of 17 with the cyclic aminal of 24 resulted solely in the
formation of the corresponding tetrahydrodiazepine 25
when 24 was treated with the p-chlorophenyl-substituted
acetylenic sulfone 1b.13 Finally, the N-(benzenesulfonyl)-
pyrrole analogue 26 reacted with 1a in the same way as
N-benzylindole 4, producing tetrahydroazepine 27 (Scheme 6).
Thus, all of the heteroaromatic compounds investigated,
Experimental Section
(12) Anionic 6π-electron electrocyclic reactions are relatively rare but
have been reported previously. For example, the disrotatory ring-closure of
the cyclooctadienyl anion produces the corresponding cis-fused
[3.3.0]bicyclooctene species after protonation, similarly to the present case.
See: Bates, R. B.; McCombs, D. A. Tetrahedron Lett. 1969, 10, 977–978.
(13) The use of 1a in this experiment produced a more complex mixture of
products. Compound 1b is more electrophilic than 1a and may facilitate the
initial conjugate addition step by better stabilizing the resulting vinyl anion.
General Experimental. NMR spectra were recorded in deu-
teriochloroform and mass spectra were obtained by electron
impact, unless otherwise indicated. The preparation and char-
acterization of the starting materials 9, 11, 13, 15, 18, 24, and 26
are described in the Supporting Information. Acetylenic sul-
fones 1a and 1b were prepared by literature methods.5b,14
5404 J. Org. Chem. Vol. 75, No. 15, 2010

Weston et al.
JOCNote
Preparation of 1-Benzyl-2-(1-benzylpyrrolidin-2-yl)-1H-indole
(4). 1-Benzyl-2-(pyrrolidin-2-yl)-1H-indole was prepared by a
literature method15 and the pyrrolidine moiety was N-benzy-
lated with benzyl bromide-triethylamine in dichloromethane by
the same general procedure as in the preparation of 17 (vide
dichloromethane at 0 °C. The mixture was stirred at 0 °C for 2 h,
quenched with saturated NaHCO3 solution, extracted with
dichloromethane, dried, concentrated, and purified by flash
chromatography (50% ethyl acetate-hexanes) to afford 983
mg (67%) of 1-benzenesulfonyl-2-(4,5-dihydro-3H-pyrrol-2-
yl)-1H-indole as a pale yellow solid. This was dissolved in
ethanol (40 mL) and sodium borohydride (3.50 g, 92.5 mmol)
was added in portions over 2 d. The mixture was concen-
trated, dissolved in ethyl acetate, washed with aqueous NaOH,
dried, and concentrated to produce crude 1-benzenesulfonyl-
2-(pyrrolidin-2-yl)-1H-indole, which was dissolved in dichlor-
omethane (25 mL), along with triethylamine (0.84 mL, 6.1
mmol) and benzyl bromide (0.36 mL, 3.0 mmol). The mixture
was stirred overnight, washed with saturated NaHCO3 solution,
dried, concentrated, and purified via flash chromatography
(10% ethyl acetate-hexanes) to afford 695 mg (56%) of 17 as a
pale yellow oil: IR (film) 1448, 1371, 1173 cm-1; 1H NMR (300
MHz) δ 8.25 (d, J = 7.7 Hz, 1H), 7.75 (d, J = 8.4 Hz, 2H),
7.52-7.19 (m, 11H), 7.02 (s, 1H), 4.30-4.25 (m, 1H), 3.90 (d,
J = 13.0 Hz, 1H), 3.18 (d, J = 13.0 Hz, 1H), 3.11-3.08 (m,
1H), 2.55-2.47 (m, 1H), 2.29 (dd, J = 16.7, 8.8 Hz, 1H),
1.90-1.73 (m, 3H); 13C NMR (75 MHz) δ 146.2, 139.8, 139.4,
137.8, 133.7, 129.9, 129.2, 128.5, 128.3, 126.9, 126.2, 124.0,
123.7, 120.7, 114.9, 108.6, 62.5, 59.2, 53.6, 34.4, 23.2; mass
spectrum m/z (%) 416 (Mþ, 25), 324 (45), 275 (100), 91
(65). HRMS Calcd for C25H24N2O2S, 416.1559; found,
416.1557.
infra) to afford 4 in 84% yield: IR (film) 1605, 1453, 1162 cm-1
;
1H NMR (300 MHz) δ 7.74 (m, 1H), 7.38-7.15 (m, 11H), 7.04
(d, J = 8.2 Hz, 2H), 6.76 (s, 1H), 5.94 (d, J = 17.3 Hz, 1H), 5.66
(d, J = 17.3 Hz, 1H), 4.27 (d, J = 13.1 Hz, 1H), 3.86 (t, J = 7.9
Hz, 1H), 3.26 (d, J = 13.1 Hz, 1H), 3.25 (m, 1H), 2.35-2.17 (m,
2H), 2.10-1.80 (m, 3H); 13C NMR (75 MHz) δ 142.0, 139.7,
138.5, 138.3, 128.8, 128.7, 128.2, 128.1, 127.3, 127.0, 126.0,
121.5, 120.5, 119.8, 109.9, 101.3, 62.8, 58.7, 53.4, 47.2, 32.5,
22.7; mass spectrum m/z (%) 366 (Mþ, 63), 91 (100). HRMS
Calcd for C26H26N2, 366.2096; found, 366.2083.
Reaction of 4 with Acetylenic Sulfone 1a (Typical Procedure).
Indole 4 (127 mg, 0.347 mmol) and acetylenic sulfone 1a (62 mg,
0.34 mmol) were stirred for 14 h at room temperature in 5 mL of
acetonitrile. The mixture was concentrated and purified by flash
chromatography (15-30% ethyl acetate-hexanes) to afford
167 mg (90%) 1-benzyl-5-(1-benzylindol-2-yl)-6-(p-toluenesul-
fonyl)-2,3,4,5-tetrahydro-1H-azepine (8) as white solid, mp
161-162 °C (from acetonitrile): IR (film) 1627, 1280, 1134
cm-1 1H NMR (400 MHz) δ 7.87 (s, 1H), 7.44-7.16 (m,
;
11H), 7.12-6.98 (m, 5H), 6.85 (d, J = 8.1 Hz, 2H), 5.97 (s,
1H), 5.32 (d, J = 17.3 Hz, 1H), 5.26 (d, J = 17.3 Hz, 1H), 4.50
(d, J = 15.0 Hz, 1H), 4.40 (d, J = 15.0 Hz, 1H), 4.36 (t, J = 3.6
Hz, 1H), 3.52-3.50 (m, 1H), 2.96-2.91 (m, 1H), 2.13 (s, 3H),
1.74-1.67 (m, 3H) 1.50-1.43 (m, 1H); 13C NMR (75 MHz) δ
149.5, 142.1, 140.3, 139.8, 137.8, 137.3, 137.1, 128.9, 128.68,
128.65, 128.1, 127.6, 127.3, 126.8, 126.1, 121.0, 119.8, 119.4,
109.4, 109.0, 103.6, 63.6, 52.6, 46.5, 35.4, 31.7, 23.5, 21.2; mass
spectrum m/z (%) 546 (Mþ, 51), 455 (46), 391 (100). HRMS
Calcd for C35H34N2O2S, 546.2341; found, 546.2344.
Reaction of 17 with Acetylenic Sulfone 1a (Typical Procedure).
Indole 17 (100 mg, 0.240 mmol) and acetylenic sulfone 1a (43
mg, 0.24 mmol) were stirred for 24 h at room temperature in 5
mL of acetonitrile. The mixture was concentrated and purified
via flash chromatography (15-30% ethyl acetate-hexanes),
affording 136 mg (95%) of 5-benzenesulfonyl-1-benzyl-10-(p-
toluenesulfonyl)-1,2,3,4,4a,5,10,10a-octahydro-pyrido[20,30:4,5]-
cyclopenta[1,2-b]indole (22) as a pale yellow solid: mp 132-
135 °C (from toluene-hexanes); IR (film) 1596, 1449, 1366,
The preparation and characterization data for the other
products in Table 1, as well as for 23, 25, and 27, are provided
in the Supporting Information.
1
1184 cm-1; H NMR (300 MHz) δ 7.96 (d, J = 8.0 Hz, 1H),
Preparation of 1-Benzenesulfonyl-2-(1-benzylpyrrolidin-2-yl)-
1H-indole (17). N-(Benzenesulfonyl)indole16 (2.00 g, 7.77 mmol)
and TMEDA (0.93 g, 8.0 mmol) were dissolved in THF (50 mL),
cooled to -78 °C, and n-butyllithium (3.11 mL, 2.5 M in
hexanes, 7.8 mmol) was added slowly. The red solution was
warmed to room temperature over 2 h and was then cooled back
to -78 °C. N-t-Butyloxycarbonyl-2-pyrrolidinone (1.44 g, 7.77
mmol) was added and the mixture was stirred at -78 °C for 1 h
and then at room temperature for 1 h. Brine was added and the
mixture was extracted with ethyl acetate, dried, and concen-
trated. The residue was purified by flash chromatography (25%
ethyl acetate-hexanes) to give 2.02 g (58%) of [4-(1-benzene-
sulfonyl-1H-indol-2-yl)-4-oxo-butyl]-carbamic acid tert-butyl
ester as a yellow oil.
7.63 (d, J = 7.4 Hz, 2H), 7.56-7.50 (m, 2H), 7.35-7.20 (m, 11H),
6.94 (d, J = 7.9 Hz, 2H), 4.92 (d, J = 4.4 Hz, 1H), 4.30 (dd, J =
7.7, 4.7 Hz, 1H), 4.00 (d, J = 14.0 Hz, 1H), 3.75 (d, J = 13.8 Hz,
1H), 3.73 (m, 1H), 2.64-2.58 (m, 1H), 2.54-2.41 (m, 1H),
2.34 (s, 3H), 2.27-2.15 (m, 1H), 1.88-1.75 (m, 1H), 1.60-1.47
(m, 1H), 1.09-0.95 (m, 1H); 13C NMR (75 MHz) δ 149.5, 144.7,
140.5, 139.6, 138.2, 134.3, 134.1, 129.8, 129.6, 129.6, 128.9, 128.8,
128.7, 127.4, 126.9, 125.0, 124.7, 121.6, 119.5, 115.0, 68.5, 66.5,
59.1, 45.0, 39.3, 25.7, 22.1, 17.6; massspectrumm/z (%) 455 (100),
209 (50), 91 (46). HRMS Calcd for C28H27N2O2S (Mþ - C6H5-
SO2), 455.1793; found, 455.1780.
Acknowledgment. We thank the Natural Sciences and
Engineering Research Council of Canada for financial sup-
port and Detian Gao for recording several spectra.
Trifluoroacetic acid (1.08 mL, 14.6 mmol) was added drop-
wise to a solution of the above product (2.02 g, 4.52 mmol) in
(14) (a) Chen, Z.; Trudell, M. L. Synth. Commun. 1994, 24, 3149–3155.
(b) Bhattacharya, S. N.; Josiah, B. M.; Walton, D. R. M. Organomet. Chem.
Synth. 1971, 1, 145–149.
(15) Street, J. D.; Harris, M.; Bishop, D. I.; Heatley, F.; Beddoes, R. L.;
Mills, O. S.; Joule, J. A. J. Chem. Soc., Perkin Trans. 1 1987, 1599–1606.
(16) Saulnier, M. G.; Gribble, G. W. J. Org. Chem. 1982, 47, 757–761.
Supporting Information Available: Characterization data
1
and H and 13C NMR spectra of new compounds; 2D NMR
spectra of 10; X-ray crystallographic data for 8 and 22. This
material is available free of charge via the Internet at http://
pubs.acs.org.
J. Org. Chem. Vol. 75, No. 15, 2010 5405