Synthesis of highly substituted dibenzoazocine derivatives by the aza-Claisen rearrangement and intramolecular Heck reaction via 8-exo-trig mode of cyclization

Article abstract of DOI:10.1016/j.tetlet.2009.01.105

The synthesis of highly substituted dibenzo-azocine systems is still lacking. An efficient synthetic protocol utilizing the sequential aromatic aza-Claisen rearrangement followed by the implementation of the intramolecular Heck reaction as a key step has been developed for the synthesis of various dibenzo-azocine derivatives of biological relevance.

Full text of DOI:10.1016/j.tetlet.2009.01.105

Tetrahedron Letters 50 (2009) 3178–3181
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis of highly substituted dibenzoazocine derivatives by the
aza-Claisen rearrangement and intramolecular Heck reaction via
8-exo-trig mode of cyclization
*
K. C. Majumdar , Buddhadeb Chattopadhyay, Srikanta Samanta
Department of Chemistry, University of Kalyani, Kalyani 741 235, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of highly substituted dibenzo-azocine systems is still lacking. An efficient synthetic proto-
col utilizing the sequential aromatic aza-Claisen rearrangement followed by the implementation of the
intramolecular Heck reaction as a key step has been developed for the synthesis of various dibenzo-azo-
cine derivatives of biological relevance.
Received 12 December 2008
Revised 9 January 2009
Accepted 18 January 2009
Available online 23 January 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Aza-Claisen rearrangement
Heck reaction
Dibenzoazocine
8-Exo-trig
Medium-sized nitrogen heterocycles, especially eight-mem-
bered azocines, are key intermediates occurring in many natural
products.1,2 Besides, medium-sized heterocycles fused to aryl rings
are found in many drugs and preclinical leads. An important scaf-
fold is the dibenzo[b,f]azocine present in psychotropic drugs such
as Imipramine, Desipramine and Bonnecore.3 Despite their biolog-
ical activity, azocine fused systems are not sufficiently investi-
gated, one possible barrier to this generally being unsatisfactory
synthetic procedures.4
Modern organic synthesis emphasizes the utilization of reac-
tions that require a minimal amount of labour and allow for the
construction of complex molecules in a time and cost effective
manner. During the past decade, major efforts have been devoted
to the development of palladium-mediated organic reactions,
which, by virtue of their ease of compatibility, complexity and
diversity, may bring about potential and highly effective transfor-
mation.5 Recently, the search of more novel methods for the con-
struction of organic molecules from simple starting materials has
been an ongoing challenge. In general, not many methods are
available for the synthesis of medium-sized heterocycles. Among
the various synthetic protocols, the palladium-catalyzed intramo-
lecular Heck reaction has become a useful technique due to its
excellent functional group tolerance and high stereoselectivity. Re-
cently, we have reported6 the synthesis of some interesting regular
to medium-ring oxa- and oxathia- heterocycles by the application
of the intramolecular Heck reaction. However, other groups7 have
also reported the formation of medium-sized heterocyclization by
palladium-catalyzed Heck reactions, but none has started with the
unactivated allylic C–H activation method. Moreover, though the
formation of medium-sized oxa-heterocycles is relatively abun-
dant,6,8 medium-sized nitrogen heterocycles by the implementa-
tion of intramolecular Heck reactions are rare and still significant
from the synthetic point of view. It is reported9 that palladium-
catalyzed cyclization by the application of intramolecular Heck
reactions require harsh reaction conditions where a nitrogen-con-
taining compound is used as the starting material. Recently, Guy
et al10 have presented eight-membered azocines by the intramo-
lecular Heck reaction via the 8-endo-trig mode of cyclization start-
ing from highly activated precursors. Therefore, all the findings
prompted us to undertake the synthesis of biologically interesting
azocine intermediates by the application of the palladium-medi-
ated intramolecular Heck reaction via the 8-exo-trig mode of cycli-
zation starting from unactivated allylic systems.
The aza-Claisen rearrangement of N-allylaniline under thermal
conditions requires drastic conditions11 compared to the corre-
sponding oxy-Claisen rearrangement. However, such rearrange-
ment generally occurs with
a significant amount of rate
enhancement under catalyzed conditions.11,12 Moreover, it has
been found that the presence of an additional13 alkyl group in
the N-alkylaniline greatly increases the rate of the aromatic aza-
Claisen rearrangement. Usually, it is a tough job to accomplish
the aromatic aza-Claisen rearrangement without using an addi-
tional alkyl group in the N-allyl moiety and this is due to the fact
* Corresponding author. Tel.: +91 033 25827521; fax: +91 033 582 8282.
E-mail address: kcm_ku@yahoo.co.in (K.C. Majumdar).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.01.105

K. C. Majumdar et al. / Tetrahedron Letters 50 (2009) 3178–3181
3179
Table 1
that under catalyzed conditions the rearranged C-allyl product
immediately cyclizes to give the corresponding indoline14 deriva-
tives. Besides, a number of unidentified side products are also
formed. Therefore, this led us to explore a selective monorear-
rangement products of N-allylaniline derivatives as a possible
route for the preparation of our desired Heck precursors for the
ultimate preparation of the corresponding dibenzo-azocine
derivatives.
Accordingly, we prepared N-allylaniline 2a from the reaction of
4-methylaniline 1a and allyl bromide in refluxing DMF in the pres-
ence of anhydrous potassium carbonate (Scheme 1).
Screening of experimental conditions of the aza-Claisen rearrangement
Entry
Substratea
Catalyst
Solvent
Time (h)
Yieldb (%)
1
2c
3
4
5
6
7
8
9
1a
1a
1a
1a
1a
1a
1a
1b
1c
3a
1 equiv BF3ÁEt2O
2 equiv BF3ÁEt2O
4 equiv BF3ÁEt2O
2 equiv BF3ÁEt2O
2 equiv BF3ÁEt2O
2 equiv ZnCl2
Xylene
Xylene
Xylene
o-DCB
Toluene
Xylene
Xylene
Xylene
Xylene
Xylene
12
7
7
10
12
12
12
8
55
65
ꢀ60
ꢀ52
ꢀ45
CMd
CMd
48
2 equiv AlCl3
2 equiv BF3ÁEt2O
2 equiv BF3ÁEt2O
2 equiv BF3ÁEt2O
7
7
68
10
CMd
The desired aza-Claisen rearrangement of 2a was effectively
accomplished in xylene in the presence of BF3ÁEt2O at 140 °C in a
sealed tube within a reasonably short period of time (7–8 h) to de-
liver the corresponding rearrangement product 4a as the sole prod-
uct. We have attempted various other conditions to optimize the
reaction using other high boiling solvents, changing the catalyst
employed including changing the nature of the catalyst, and
increasing the reaction time. Instead of improvement of the results,
some side products were obtained at the expense of the desired
aza-Claisen rearrangement product. Likewise, the aromatic aza-
Claisen rearrangement of other substrates were tested by varying
the substituent present in the aromatic ring under developed con-
ditions, and the outcome is depicted in Table 1. Here, it is impor-
tant to note that we have also conducted the aza-Claisen
rearrangement using the –Ts substrates 3a, but we obtained a com-
plicated reaction mixture instead of the desired product.
a
All reactions were carried out with 1.2 g substrate in 4 ml solvent at 140 °C in a
sealed tube.
b
c
Isolated yield.
Optimized reaction conditions.
CM = complex reaction mixture.
d
Br
H
Br
i
NH2
+
N
ii
NR
Br
Me
Me
4a
6a
7
Scheme 2. Reagents and conditions: (i) acetone, K2CO3, NaI, 3.5 h, reflux. (ii)
Pd(OAc)2, TBAB, KOAc, DMF, 90 °C, 10–20 h.
To this end, the Heck precursor 7 was synthesized by the reac-
tion of C-allylaniline 4a and 2-bromobenzylbromide 6a in refluxing
acetone in the presence of anhydrous K2CO3 and a small amount of
sodium iodide15 (Finkelstein condition). When the Heck reaction
was carried out with the substrate 7 in the presence of Pd(OAc)2
as catalyst, tetrabutylammonium bromide (TBAB) as additive and
Me
NH
Pd
Br
Figure 1.
Ts
H
NH2
N
N
iii
i
R
R
R
R
fused KOAc as base in DMF under a nitrogen atmosphere at
90 °C, for 10–20 h, there was no indication for the formation of
the Heck reaction product. The starting material remained un-
changed (Scheme 2).
1a, R = 4-Me
1b, R = 2-F
1c, R = H
2(a-c)
3
X
ii
ii
Ts
NH
NH2
No further improvement was observed even by increasing the
reaction temperature. Therefore, we failed to carry out the Heck
reaction starting with the substrate 7. The reason for the failure
may be due to the fact that the catalyst Pd(OAc)2 loses its catalytic
activity16 by the formation of the following type of complex
(Fig. 1).17 This may be possible through palladium expanding its
R
4(a-c)
5
Scheme 1. Reagents and conditions: (i) allyl bromide, DMF, K2CO3, reflux, 8 h. (ii)
see optimization table 1. (iii) pyridine, TsCl, heat, 4 h.
R1
Br
Ts
N
NHTs
Br
i
+
R
R
Br
R1
6, R1 = H, OMe
5
8
8a, R = 4-Me, R1 = H, 89%
8b, R = 2-F, R1 = H, 81%
8c, R = R1 = H, 90%
8d, R = 4-Me, R1 = OMe, 84%
8e, R = 2-F, R1 = OMe, 88%
8f, R = H, R1 = OMe, 86%
Ts
N
Ts
Ts
N
N
ii
and or
8
9
Br
Me
Me
Me
8a
9a
10
Scheme 3. Reagents and conditions: (i) acetone, K2CO3, NaI, 3.5 h, reflux. (ii) Pd(OAc)2, TBAB, KOAc, DMF, N2 atms, 90 °C, 6 h.

3180
K. C. Majumdar et al. / Tetrahedron Letters 50 (2009) 3178–3181
Table 2
ing acetone–K2CO3 in the presence of a small amount of NaI (Fin-
Optimization of the Heck reaction.a
kelstein condition).15 The intramolecular Heck reaction was
conducted with substrate 8a19 by applying the concept of Jeffery’s
two-phase protocol in the presence of Pd(OAc)2, KOAc and tetrabu-
tylammonium bromide (TBAB) in dry DMF under a nitrogen atmo-
sphere for 6 h. The eight-membered exo-Heck product (9a)20 was
obtained in 72% yield without any contamination of the endo-Heck
product 10 (Scheme 3).
Entries
Catalyst
Solvent
Base
Yieldsc (%)
1b
2
3
4
5
6
7
8
9
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(PPh3)2Cl2
PdCl2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
DMF
DMA
DMF
DMF
DMF
Toluene
Et3N
THF
Dioxane
CH3CN
DMF
KOAc
KOAc
NaOAc
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
72
70
66
54
NRd
NRd
NRd
25
The resulting exo-Heck product was easily characterized from
its 1H NMR spectrum, 13C NMR spectrum, HRMS and other analyt-
ical data. During the course of optimization of the exo-Heck reac-
tion, we observed that the catalyst, base, solvent, additive and
temperature also have profound effects on the reaction yield. The
optimized results for the synthesis of 9a are presented in Table 2.
From Table 2, it is seen that though the catalyst Pd(OAc)2 is
effective, PdCl2 is totally ineffective for the reaction in DMF. Among
the various catalysts used in this reaction to produce the dibenzo-
azocine derivative, Pd(OAc)2 gave the best results. The reaction
afforded no desired product under the reaction conditions de-
scribed in Table 2 (entries 5–7, 9, 11, and 12). All the reactions
were performed in the presence of TBAB as additive, since without
TBAB no cyclized product was obtained.
NRd
20
10
11
12
Et3 N
Ag2CO3
K2CO3
NRd
NRd
DMF
a
All reactions were carried out using TBAB.
Optimized reaction condition.
Isolated yield.
b
c
d
No reaction
valence shell to accommodate the lone pair of electrons of the free
NH moiety of the substrate.
In order to circumvent the possible Pd–N complex, we decided
to protect the NH moiety. All the C-allylaniline derivatives 4(a–c)
were tosylated under the conditions used in scheme 1 to give Heck
precursors 8a–f. The precursors 5 were benzylated with 6 in reflux-
The effect of bases on the reaction was also examined. Conduct-
ing the reaction in the presence of organic bases such as Et3 N
Table 3
Synthesis of dibenzo-azocines by Heck reactiona
Entries
Starting
Products
Time (h)
Yieldsb (%)
Ts
N
Ts
N
Br
1
6
72
Me
Me
F
8a19
9a20
Ts
N
Ts
N
F
Br
Br
2
3
4
5
8
73
75
79
73
79
8b
8c
9b
Ts
N
Ts
N
6
9c
Ts
N
Ts
N
Br
OMe
7
Me
F
Me
8d
9d
OMe
Ts
N
Ts
N
Br
F
OMe
OMe
9
8e
9e
OMe
Br
Ts
N
Ts
N
6
7.5
8f
9f
OMe
a
All the reactions were carried out under optimized conditions.
Isolated yield.
b

K. C. Majumdar et al. / Tetrahedron Letters 50 (2009) 3178–3181
3181
9. (a) Park, C.-H.; Ryabova, V.; Seregin, I. V.; Sromek, A. W.; Gevorgyan, V. Org. Lett.
2004, 6, 1159; (b) David, E.; Perrin, J.; Pellet-Rostaing, S.; Chabert, J. F.; Lemaire,
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Tymoschenko, M. F. Org. Lett. 2003, 5, 301; (d) Sezen, B.; Sames, D. J. Am. Chem.
Soc. 2003, 125, 5274; (e) Sezen, B.; Sames, D. J. Am. Chem. Soc. 2003, 125, 10580;
(f) Sezen, B.; Sames, D. Org. Lett. 2003, 5, 3607; (g) Rieth, R. D.; Mankad, N. P.;
Calimano, E.; Sadighi, J. P. Org. Lett. 2004, 6, 3981; (h) Okazawa, T.; Satoh, T.;
Miura, M.; Nomura, M. J. Am. Chem. Soc. 2002, 124, 5286; (i) Yokooji, A.;
Okazawa, T.; Satoh, T.; Miura, M.; Nomura, M. Tetrahedron 2003, 59, 5685; (j)
Kalyani, D.; Deprez, N. R.; Desai, L. V.; Sanford, M. S. J. Am. Chem. Soc. 2005, 127,
7330; For a review: (k) Zificsak, C. A.; Hlasta, D. J. Tetrahedron 2004, 60, 8991.
10. Arnold, L. A.; Luo, W.; Guy, R. K. Org. Lett. 2004, 6, 3005.
11. For some recent reviews on Claisen rearrangement, see: (a) Majumdar, K. C.;
Alam, S.; Chattopadhyay, B. Tetrahedron 2008, 64, 597; (b) Castro, A. M. Chem.
Rev. 2004, 104, 2939; (c) Nubbemeyer, U. Synthesis 2003, 961.
12. Roe, J. M.; Webster, R. A. B.; Ganesan, A. Org. Lett. 2003, 5, 2825.
13. Nubbemeyer, U. Top. Curr. Chem. 2005, 244, 149.
changes the outcome of the reaction and only 20% of 9a was ob-
tained. Replacement of KOAc with NaOAc was also found to be
effective (entry 3). The effects of other bases were also studied,
and the use of Ag2CO3 was found to be ineffective.
A study of the solvent effect (DMF, MeCN, 1,4-dioxane, THF, tol-
uene, Et3 N) suggested that DMF is the best choice. After achieving
the optimized results, other substrates 8b–f were similarly treated
under optimized reaction conditions to afford the corresponding
exo-Heck cyclized products dibenzo-azocines derivatives 9b–f in
72–79% yields. The results are summarized in Table 3.
The formation of medium-sized exo-, and endo-Heck products is
quite difficult. The formation of the exo-Heck product is favoured be-
cause of the less steric as well as transannular interaction.18 The dib-
enzoazocines were obtained through a 8-exo-trig mode of cyclization.
In conclusion, we have developed an efficient synthetic strategy
for the selective aromatic aza-Claisen rearrangement of free NH-
allylated aniline derivatives for the preparation of N-tethered Heck
precursors possessing diversity relevant to drug design and drug
discovery. The protocol is simple, straightforward and interesting.
A synthetic route for the construction of the dibenzoazocine from
unactivated allylic substrates by the intramolecular Heck reaction
has been developed.
14. Correa, A.; Tellitu, I.; Dominguez, E.; Sanmartin, R. J. Org. Chem. 2006, 71, 8316.
15. (a) Gazith, M.; Noys, R. M. J. Am. Chem. Soc. 1955, 77, 6091; (b) Gardner, I. J.;
Noys, R. M. J. Am. Chem. Soc. 1961, 83, 2409.
16. Majumdar, K. C.; Chattopadhyay, B.; Nath, S. Tetrahedron Lett. 2008, 49, 1609.
17. Tsuji, J.. Palladium Reagents and Catalysts. In New Perspective for the 21st
Century; Wiley, 2004. 2nd Chapter.
18. (a) Illuminati, G.; Mandolini, L. Acc. Chem. Res. 1981, 14, 95; (b) Beletskaya, I. P.;
Cheprakov, A. V. Chem. Rev. 2000, 100, 3009.
19. Some selected spectral data: Synthesis of Heck precursors 8a: A mixture of the
compounds 5a (210 mg, 0.697 mmol) and 2-bromobenzylbromide 6a
(191.9 mg, 0.767 mmol) and dry K2CO3 (1.0 gm) in dry acetone (50 ml) in the
presence of sodium iodide was refluxed for 3.5 h. The reaction mixture was
cooled and filtered, and the solvent was removed. The residual mass was
extracted with chloroform (3 Â 30 ml), washed with water followed by brine-
water and dried (Na2SO4). Removal of chloroform gave a crude product, which
was chromatographed over silica gel (60–120 mesh). Elution of the column
with pet. ether–ethyl acetate (5%) gave compounds 8a.Compound 8a: Yield
89%.; solid; mp 79–80 °C.IR (KBr, cmÀ1): 1149, 1338, 2852, 2911.1H NMR
(CDCl3, 400 MHz): dH = 2.24 (s, 3H, CH3), 2.45 (s, 3H, CH3), 3.18 (d, 2H,
J = 6.6 Hz, @CH–CH2), 4.48 (d, 1H, J = 13.7 Hz, N–CHaHb), 4.89 (dd, 1H,
J = 11.2 Hz, J = 3.0 Hz, @CHaHb), 4.93 (dd, 1H, J = 17.2 Hz, J = 3.0 Hz, @CHaHb),
5.09 (d, 1H, J = 13.7 Hz, N–CHaHb), 5.36–5.46 (m, 1H, @CH), 6.58 (d, 1H,
J = 8.1 Hz, ArH), 6.82 (d, 1H, J = 8.1 Hz, ArH), 6.91 (s, 1H, ArH), 7.04 (t, 1H,
J = 7.6 Hz, ArH), 7.17 (t, 1H, J = 7.6 Hz, ArH), 7.30 (d, 2H, J = 7.9 Hz, ArH), 7.39 (d,
2H, J = 7.8 Hz, ArH), 7.60 (d, 2H, J = 7.9 Hz, ArH).13C NMR (CDCl3, 75 MHz):
dC = 21.1, 21.6, 34.8, 55.1, 116.1, 124.4, 127.1, 127.3, 128.0, 128.1, 129.3, 129.5,
130.7, 131.9, 132.7, 134.2, 134.9, 135.5, 136.8, 138.2, 141.2, 143.6.HRMS:
Calculated for C24H24BrNO2S: 492.0609 (M+), 494.0609 (M+2). Found:
492.0609 (M+), 494.0591 (M+2).Anal. Calcd for C24H24BrNO2S: C, 61.28; H,
5.14; N, 2.98. Found: C, 61.58; H, 4.89; N, 3.11.
Acknowledgements
We thank the CSIR (New Delhi) and the DST (New Delhi) for
financial assistance. Two of us (B.C. and S.S.) are grateful to the CSIR
(New Delhi) for
respectively.
a senior and a junior research fellowship,
References and notes
1. Bertha, C. M.; Ellis, M.; Filippen-Anderson, J. L.; Porreca, F.; Rothman, R. B.;
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4. Gil, L.; Gil, R. P. d. F.; dos Santos, D. C.; Marazano, C. Tetrahedron Lett. 2000, 41,
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5. (a) Gulias, M.; Garcia, R.; Delgado, A.; Castedo, L.; Mascarenas, J. L. J. Am. Chem.
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Tommasi, S.; Bonchi, A. U. J. Am. Chem. Soc. 2006, 128, 1424; (c) Yip, K. T.; Yang,
M.; Law, K. L.; Zhu, N. Y.; Yang, D. J. Am. Chem. Soc. 2006, 128, 3130; (d) Kamijo,
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Chattopadhyay, B.; Sinha, B. Tetrahedron Lett. 2008, 49, 1319; (d) Majumdar, K.
C.; Sinha, B.; Chattopadhyay, B.; Ray, K. Tetrahedron Lett. 2008, 49, 4405; (e)
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Majumdar, K. C.; Mondal, S.; De, N. Synlett 2008, 2851.
20. General procedure for the synthesis of the compounds 9 by Heck reaction: A
mixture of 8a (100 mg, 0.212 mmol), tetrabutylammonium bromide
(82.41 mg, 0.255 mmol) and dry potassium acetate (52.12 mg, 0.531 mmol)
was taken in dry N,N-dimethylformamide (DMF) (10 mL) under nitrogen
atmosphere. Pd(OAc)2 (10 mol %, 4.76 mg) was added, and the reaction
mixture was stirred at 90 °C for 6 h. The reaction mixture was cooled, water
(20 mL) was added, extracted with ethyl acetate (3 Â 30 mL) and the ethyl
acetate extract was washed with water (2 Â 40 mL), followed by brine (30 mL).
The organic layer was dried (Na2SO4), and the solvent was distilled off to
furnish a viscous mass, which was purified by column chromatography over
silica gel. Elution of the column with 4% ethyl acetate-petroleum ether afforded
the product 9a.
Compound 9a: Yield 72%; solid; mp 138–139 °C. IR (KBr, cmÀ1): 1147, 1330.1H
NMR (CDCl3, 400 MHz): dH = 2.18 (s, 3H, CH3), 2.42 (s, 3H, CH3), 3.20 (s, 2H,
CH2), 4.97 (br s, 1H, N–CHaHb), 4.99 (br s, 1H, N-CHaHb), 5.00 (d, 1H, J = 1.1 Hz,
@CHaHb), 5.13 (d, 1H, J = 1.1 Hz, @CHaHb), 6.74–6.78 (m, 2H, ArH), 6.83 (s, 1H,
ArH), 7.01 (d, 2H, J = 6.9 Hz, ArH), 7.10–7.16 (m, 3H, ArH), 7.32–7.35 (m, 1H,
ArH), 7.38-7.45 (m, 2H, ArH).
7. (a)Gibson,S. E.; Guillo, N.; Jones, J. O.;Buck, I. M.; Kalindjian, S. B.; Roberts, S.;Tozer,
M. J. Eur. J. Med. Chem. 2002, 37, 379; (b) Gibson, S. E.; Guillo, N.; Middleton, R. J.;
Thuilliez, A.; Tozer, M. J. J. Chem. Soc., Perkin Trans. 1 1997, 447; (c) Gibson, S. E.;
Middleton,R.J.J. Chem.Soc., Chem.Commun. 1995,1743;(d)Gibson,S.E.;Jones,J.O.;
McCague, R.;Tozer,M.J.;Whitcombe,N.J. Synlett1999, 954;(e)Gibson, S. E.;Guillo,
N.; Kalindjian, S. B.; Tozer, M. J. Bioorg. Med. Chem. Lett. 1997, 7, 1289; (f) Gibson, S.
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Arnold, L. A.; Guy, R. K. Bioorg. Med. Chem. Lett. 2006, 16, 5360.
13C NMR (CDCl3, 75 MHz): dC = 20.9, 21.5, 54.9, 126.3, 126.6, 127.2, 127.3,
127.5, 127.8, 127.9, 128.1, 128.6, 128.8, 128.9, 129.2, 129.5, 130.2, 130.5, 130.9,
131.8, 132.4, 138.1, 143.2, 147.8.
HRMS: Calculated for C24H23NO2S: 412.1347 (M+Na)+. Found: 412.1347
(M+Na)+.
Anal. Calcd for C24H23NO2S: C, 74.00; H, 5.95; N, 3.60. Found: C, 74.19; H, 5.77;
N, 3.71.
8. (a) Alcaide, B.; Almendros, P.; Rodriguez-Acebes, R. J. Org. Chem. 2005, 70, 2713;
(b) Molander, G. A.; Dehmel, F. J. Am. Chem. Soc. 2004, 126, 10313.