Synthesis of azepine- and azocine-annulated heterocycles by aromatic aza-Claisen rearrangement and ring-closing metathesis

Article abstract of DOI:10.1055/S-0029-1218620

Syntheses of hitherto unreported azepine- and azocine-annulated heterocycles have been developed in excellent yields via a catalyzed aromatic aza-Claisen rearrangement followed by ring-closing metathesis using Grubbs first-generation catalyst. Georg Thiem

Full text of DOI:10.1055/S-0029-1218620

PAPER
863
Synthesis of Azepine- and Azocine-Annulated Heterocycles by Aromatic
Aza-Claisen Rearrangement and Ring-Closing Metathesis
Synthesis of
A
zepi
.
ne- andAz
o
C
cine-AnnulatedH
.
eterocyclesMajumdar,* Srikanta Samanta, Buddhadeb Chattopadhyay, Raj Kumar Nandi
Department of Chemistry, University of Kalyani, Kalyani 741235, W.B., India
E-mail: kcm_ku@yahoo.co.in
Received 2 November 2009; revised 5 November 2009
compounds that possesses this type of moiety is the syn-
thetic benzofuroazocines, which, due to their structure
close to that of hypnoanalgesics, possess important activ-
ity in the central nervous system.9 Moreover, these com-
pounds have uses, for example D has been used as a site-
specific cocaine abuse treatment agent, natural product
supinine C E as been used as an anti-insectan, and F has
anti-exploratory behavior in mice. Despite their wide
range of biological activity, azepine- and azocine-fused
systems have not been sufficiently investigated. One pos-
sible barrier to this may be the lack of satisfactory synthet-
ic procedures.
Abstract: Syntheses of hitherto unreported azepine- and azocine-
annulated heterocycles have been developed in excellent yields via
a catalyzed aromatic aza-Claisen rearrangement followed by ring-
closing metathesis using Grubbs first-generation catalyst.
Key words: azepine, azocine, aza-Claisen rearrangement, ring-
closing metathesis
It is well documented that the thermal aza-Claisen rear-
rangement requires drastic1 conditions compared to the
corresponding oxy-Claisen rearrangement. However,
such rearrangements usually take place with a significant
rate enhancement when there is an additional alkyl group
on the substrate (i.e., N-alkyl, N-allyl). Recently, Alajarín
et al. reported2 the aromatic aza-Claisen rearrangement of
N-allyl-1-naphthylamines under thermal conditions by
utilization of the standard protocol of Marcinkiewicz et
al.3 and Inada and Kurata4 and the corresponding C-allyl
product was eventually obtained in only 50% yield togeth-
er with a considerable amount of starting material and cy-
clized product (Scheme 1). Therefore, it is evident that the
aromatic aza-Claisen rearrangement remains largely un-
explored under catalyzed conditions.
O
H
N
H
N
Cl
C
OMe
NH
NH
B
A
O
Ph
CO2Me
O
HN
NH
H
OH
HO
O
D
E
HN
NH2
HN
HN
H
N
+
+
O
N
Cl
HO
O
N
N
Scheme 1 Aza-Claisen rearrangement of Alajarin et al.
G
Me
F
Medium-sized nitrogen heterocycles,5 especially seven-
and eight-membered azepine and azocine derivatives6 are
important and are found in a number of natural and non-
natural products.7 These heterocyclic skeletons are
present in complex structures of many substances e.g. A–
J (Figure 1). Among non-natural products, the more com-
monly found azepines or azocines are substituted and ful-
ly or partly reduced. These compounds have attracted
great attention for application as therapeutic agents in
view of their biological activity, for example as antimalar-
ials, antitussives, nasal decongestants, antihypertensives,
and analgesics.8 Another large and much-studied class of
N
OMe
N
O
N
H
MeO
H
O
H
O
Br
O
I
O
OMe
R
N
N
Br
NHMe
R = H, Me
N
J
Figure 1 Some bioactive compounds possessing azepine and azo-
cine rings
SYNTHESIS 2010, No. 5, pp 0863–0869
Advanced online publication: 22.12.2009
x
x
.
x
x
.2
0
1
0
DOI: 10.1055/s-0029-1218620; Art ID: Z23309SS
© Georg Thieme Verlag Stuttgart · New York

864
K. C. Majumdar et al.
PAPER
Recently, we reported the synthesis of some interesting
medium-sized heterocycles by application of the intramo-
lecular Heck reaction sequence.10 Moreover, we also
reported11 the synthesis of some important oxepine and
oxocine derivatives in excellent yields by a new route that
involves tandem Claisen rearrangement followed by ring-
closing metathesis reaction.
Table 1 Optimization of the Aza-Claisen Rearrangement
Entry
Substrate
Catalyst
PhNEt2
ZnCl2
Solvent
neat
Yield (%)
1
2
3
4
5
6
7
2a
2a
2a
2a
2a
2a
2b
15a
b
CH2Cl2
CH2Cl2
xylene
toluene
xylene
xylene
–
b
AlCl3
–
c
AlCl3
–
R1
R1
iv
R2
BF3·OEt2
BF3·OEt2
BF3·OEt2
70
85
65
R2
4α, R1 = 1-NH-allyl, R2 = 2-allyl
4β, R1 = 2-NH-allyl, R2 = 1-allyl
5α, R1 = 1-NMe-allyl, R2 = 2-allyl
5β, R1 = 2-NMe-allyl, R2 = 1-allyl
iii
R1
R1
R1
a Plus deallylated product.
b No reaction.
i
ii
R2
c Complicated reaction mixture.
1α, R1 = 1-NH2
1β, R1 = 2-NH2
3α, R1 = 1-NH2, R2 = 2-allyl
3β, R1 = 2-NH2, R2 = 1-allyl
2α, R1 = 1-NH-allyl
2β, R1 = 2-NH-allyl
by the same reaction condition but replacing allyl bromide
by homoallyl bromide and propargyl bromide, respective-
ly.
v
R1
R1
vi
R2
R2
Attempts to carry out the metathesis reaction12 of the sub-
strate 4a with Grubbs first-generation catalyst in dichlo-
romethane–toluene or xylene at 25 °C was unsuccessful.
Decomposition of the catalyst occurred when the reaction
was conducted under refluxing condition. The RCM reac-
tion of the substrate 5a also failed, perhaps due to the co-
ordination of the lone pair of the nitrogen atom of the
substrate with the Grubbs catalyst. We next decided to
carry out the reaction with the substrate 7aa having an
electron-withdrawing group at the nitrogen atom to shield
the availability of the lone pair. When the substrate was
allowed to react in the presence of Grubbs first-generation
catalyst under a nitrogen atmosphere at 25 °C, the corre-
sponding cyclized product 10aa was obtained in excellent
yield (96%) (Scheme 3 and Table 2, entry 1).
7αa, R1 = 1-NTs-allyl, R2 = 2-allyl
7αb, R1 = 1-NTs-homoallyl, R2 = 2-allyl
7αc, R1 = 1-NTs-propargyl, R2 = 2-allyl
7βa, R1 = 2-NTs-allyl, R2 = 1-allyl
6α, R1 = 1-NHTs, R2 = 2-allyl
6β, R1 = 2-NHTs, R2 = 1-allyl
7βb, R1 = 2-NTs-homoallyl, R2 = 1-allyl
Scheme 2 Reagent and conditions: (i) allyl bromide, K2CO3, ace-
tone, 2 h, reflux, 64–65%; (ii) BF3·OEt2, xylene, 140 °C, 7 h, 65–85%;
(iii) allyl bromide, K2CO3, acetone, 3 h, reflux, 59–60%; (iv) MeI,
K2CO3, EMK, NaI, 6 h, reflux, 61–62%; (v) pyridine, TsCl, heat, 4 h,
87–92%; (vi) allyl bromide, homoallyl bromide, or propargyl bro-
mide, K2CO3, acetone, NaI, 3/3.5/3.5 h, reflux, 93–95%.
All these reasons prompted us to undertake the synthesis
of potentially bioactive azepine and azocine derivatives
via aromatic aza-Claisen rearrangement followed by ring-
closing metathesis reaction. To this end, we prepared N-
allylnaphthylamines 2 from the reaction of 1 and allyl bro-
mide in refluxing acetone in the presence of anhydrous
potassium carbonate (Scheme 2). The aza-Claisen rear-
rangement of 2a was effectively carried out in xylene in
the presence of boron trifluoride–diethyl ether complex at
140 °C in a sealed tube within a reasonably short period of
time (7 h) delivering the corresponding rearrangement
product 3a as the sole product in 85% yield. We also stud-
ied different reaction conditions to optimize the yield us-
ing other high boiling solvents and by changing the
catalyst. As can be seen from Table 1, altering the condi-
tions did not result in an improvement in the yield of 2a,
instead side products were obtained at the expense of the
desired aza-Claisen product. Similarly, the aza-Claisen
rearrangements of other substrates were accomplished by
changing the substituent present in the aromatic ring and
utilizing the optimized reaction conditions.
R
N
TsN
RCM
RCM
i
no reaction
i
R = Ts
R = H
R = Me
10αa
4α R = H
5α R = Me
7αa R = Ts
Scheme 3 Reagents and conditions: (i) Grubbs I (5 mol%), CH2Cl2,
r.t., stirring, 30 min.
Similarly, the diallyl substrate 7ba derived from 2-naph-
thylamine gave the corresponding cyclized product 10ba
in 95% isolated yield under the RCM conditions (Table 2,
entry 4). We have also achieved the synthesis of the eight-
membered azocine derivatives 10ab and 10bb from the
substrates 7ab and 7bb, respectively, containing the ho-
moallyl moiety (entries 2 and 5). To test the scope and
generality of the protocol we also attempted the ring-
closing enyne metathesis reaction of the substrate 7ac.
The reaction did not occur when the ring-closing enyne
metathesis was conducted in dichloromethane using
Grubbs first-generation catalyst. However, when the reac-
The RCM precursors 4a and 7aa were prepared by the re-
action of C-allyl product 3a and 6a with allyl bromide in
refluxing acetone in the presence of anhydrous potassium
carbonate. Other precursors 7ab and 7ac were prepared
Synthesis 2010, No. 5, 863–869 © Thieme Stuttgart · New York

PAPER
Synthesis of Azepine- and Azocine-Annulated Heterocycles
865
Table 2 Synthesis of Medium-Sized Heterocycles by RCM Using Grubbs I Catalyst
Entry
1
Substrate
Conditions
Products
Yielda (%)
b
NR
RN
4a R = H
5a R = Me
7aa R = Ts
8a R = H
9a R = Me
10aa R = Ts
–
–
b
CH2Cl2, r.t., 30 min
96
NTs
TsN
2
3
7ab
7ac
CH2Cl2, r.t., 45 min
toluene, 110 °C, 10 h
10ab
10ac
94
TsN
TsN
61
4
5
7ba
7bb
CH2Cl2, r.t., 35 min
CH2Cl2, r.t., 50 min
10ba
10bb
95
89
NTs
NTs
NTs
NTs
b
R
13a R = H
13b R = Me
17a R = H
17b R = Me
–
N
6
7
CH2Cl2, r.t., 10 h
NR
35
O
O
O
O
O
O
O
b
16a R = H
16b R = Ts
18a R = H
18b R = Ts
–
CH2Cl2, r.t., 40 min
89
NR
O
N
R
a Isolated yield.
b No reaction.
tion was carried out in refluxing toluene at 110 °C for 10 (Table 2, entry 6). We then modified the substrate by re-
hours using the same catalyst we were pleased to obtain placing NH with NMe (electron-releasing). N-Methyl de-
the corresponding cyclized product 10ac in good yield rivative 13b was found to be an ineffective substrate; the
(61%) (entry 3).
azepine derivative 17b was obtained in only 35% yield
when the reaction was carried out with Grubbs first-
generation catalyst. The yield of the product could not be
improved by varying the reaction conditions. Finally, we
conducted the RCM with the precursor derived from 7-
aminocoumarin (entry 7). Here the substrate 16b contain-
ing an N-tosyl group afforded the RCM product 18b in ex-
cellent yield (89%). The results are summarized in
Table 2.
We then extended the RCM reaction to heterocyclic sub-
strates. The aza-Claisen rearrangement was accomplished
successfully under the aforesaid conditions and the rear-
ranged products were obtained in good yields. The precur-
sors 13a,b and 16a,b for the ring-closing metathesis were
synthesized using the aza-Claisen rearrangement products
12a,b and 15a,b as shown in Scheme 4.
The starting materials 13a,b and 16a,b were synthesized
using the previous route and then the RCM reactions were
attempted. Reaction of free amine substrate 13a under
RCM conditions, as expected, gave no cyclized product
In conclusion, we have developed a suitable protocol for
the aza-Claisen rearrangement of both carbocyclic and
heterocyclic systems by the application boron trifluoride–
Synthesis 2010, No. 5, 863–869 © Thieme Stuttgart · New York

866
K. C. Majumdar et al.
PAPER
2a. Similarly compounds 2b,14 11a,15 11b,15 and 1416 were pre-
pared.
NH
i
NH
NH2
ii
2-Allyl-1-naphthylamine (3a);14 Typical Procedure
O
O
O
O
O
O
O
O
O
A mixture of 2a (1.2 g, 6.5 mmol) and BF3·OEt2 (1.64 mL, 13.1
mmol) in xylene (4 mL) was heated in a sealed tube at 140 °C for 7
h. After cooling the mixture was neutralized with sat. NaHCO3 soln
and extracted with EtOAc (3 × 20 mL), washed with H2O (2 × 10
mL) followed by brine (10 mL), and dried (Na2SO4). Removal of
EtOAc afforded a crude mass that was purified by column chroma-
tography (3% EtOAc–PE) to give 3a. Similarly, compounds 3b,14
12a, 12b, and 15a were prepared.
11a
12a
13a
NMe
NMe
NHMe
iv
iii
O
O
O
vi
O
11b
12b
13b
v
5-Allyl-6-amino-2H-1-benzopyran-2-one (12a)
Solid; yield: 87%; mp 92–93 °C.
IR (KBr): 3404, 3322, 1724, 1568 cm–1.
O
O
NH2
O
NH
O
O
N
H
14
15a
16a
1H NMR (400 MHz, CDCl3): d = 3.40 (d, J = 5.6 Hz, 2 H, CHCH2),
3.76 (br s, 2 H, NH2), 4.94 (d, J = 8.9 Hz, 1 H, =CHaHb), 5.14 (d,
J = 8.8 Hz, 1 H, =CHaHb), 5.94–5.99 (m, 1 H, CHCH2), 6.35 (d, J =
9.6 Hz, 1 H, H3coumarin), 6.88 (d, J = 8.8 Hz, 1 H, ArH), 7.07 (d, J =
8.8 Hz, 1 H, ArH), 7.93 (d, J = 9.6 Hz, 1 H, H4coumarin).
vii
viii
NHTs
O
O
15b
MS: m/z = 201 (M+).
O
O
N
Ts
Anal. Calcd for C12H11NO2: C, 71.63; H, 5.51; N, 6.96. Found: C,
71.50; H, 5.58; N, 7.04.
16b
Scheme 4 Reagent and conditions: (i) BF3·OEt2, xylene, 140 °C, 7
h, 87%; (ii) allyl bromide, K2CO3 acetone, 3 h, reflux, 75%; (iii)
BF3·OEt2, xylene, 140 °C, 5.5 h, 92%; (iv) allyl bromide, K2CO3,
EMK, NaI, 11 h, reflux, 75%; (v) BF3·OEt2, xylene, 140 °C, 8.5 h,
69%; (vi) TsCl, pyridine, heat, 4 h, 61%; (vii) allyl bromide, K2CO3,
acetone, NaI, reflux, 3 h, 90%; (viii) allyl bromide, K2CO3 acetone, 3
h, reflux, 94%.
5-Allyl-6-(methylamino)-2H-1-benzopyran-2-one (12b)
Solid; yield: 92%; mp 102–103 °C.
IR (KBr): 3370, 1710, 1627 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.88 (s, 3 H, CH3), 3.48–3.51 (m,
2 H, =CHCH2), 3.69 (s, 1 H, NH), 4.88–4.94 (m, 1 H, =CHaHb),
5.10–5.13 (m, 1 H, =CHaHb), 5.89–5.99 (m, 1 H, CHCH2), 6.40 (d,
J = 9.6 Hz, 1 H, H3coumarin), 6.92 (d, J = 8.8 Hz, 1 H, ArH), 7.21 (d,
J = 8.8 Hz, 1 H, ArH), 7.84 (d, J = 9.6 Hz, 1 H, H4coumarin).
diethyl ether complex, a Lewis acid catalyst for the prep-
aration of N-tethered diene and enyne precursors of the
corresponding azepine and azocine derivatives having di-
versity relevant to drug design. The methodology is sim-
ple, avoids hazardous steps, and uses easily available
starting materials and it is sufficiently flexible to permit to
the preparation of various ring sizes. This type of ring-
closing metathesis and its tolerance to both electron-
releasing and -withdrawing groups may make this process
complementary to those that exist in the literature.
MS: m/z = 215 (M+).
Anal. Calcd for C13H13NO2: C, 72.54; H, 6.09; N, 6.51. Found: C,
72.72; H, 6.01; N, 6.47.
8-Allyl-7-amino-4-methyl-2H-1-benzopyran-2-one (15a)
Solid; yield: 69%; mp 171–172 °C.
IR (KBr): 3343, 3226, 1703 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.37 (s, 3 H, CH3), 3.35 (d, J = 6
Hz, 1 H, CHCHaHb), 3.57–3.59 (m, 1 H, CHCHaHb), 3.88 (br s, 2 H,
NH2), 5.10–5.12 (m, 1 H, =CHaHb), 5.15–5.21 (m, 1 H, =CHaHb),
5.85–6.0 (m, 1 H, CHCH2), 6.04 (s, 1 H, H3coumarin), 6.62 (d, J = 8.4
Hz, 1 H, ArH), 7.32 (d, J = 8.8 Hz, 1 H, ArH).
Melting points were determined in open capillaries and are uncor-
rected. IR spectra were run for KBr discs (neat for liquid samples)
on a Perkin-Elmer 120-000A apparatus and NMR spectra were de-
termined for solns in CDCl3 with TMS as internal standard on a
Bruker DPX-300 and Bruker DPX-400. 13C NMR spectra were de-
termined for solns in CDCl3 on a Bruker DPX-300 and Bruker
DPX-400. HRMS were recorded on a Qtof Micro YA263 instru-
ment. Silica gel (60–120 mesh) was used for chromatographic sep-
aration. Silica gel G [E. Merck (India)] was used for TLC.
Petroleum ether (PE) refers to the fraction between 60 and 80 °C.
MS: m/z = 215 (M+).
Anal. Calcd for C13H13NO2: C, 72.54; H, 6.09; N, 6.51. Found: C,
72.73; H, 5.91; N, 6.47.
2-Allyl-N-tosyl-1-naphthylamine (6a); Typical Procedure
A mixture of 3a (1.2 g, 6.5 mmol) and TsCl (1.87 g, 9.8 mmol) in
pyridine (5 mL) was heated on a water bath for 4 h and then cooled
in an ice bath and left overnight. It was then extracted with EtOAc
(3 × 20 mL), washed with dil HCl (2 × 10 mL) and brine (5 mL),
and dried (Na2SO4). EtOAc was evaporated to give a crude mass
which was purified by column chromatography (silica gel, 5%
EtOAc–PE) to give 6a. Similarly, compounds 6b and 15b were pre-
pared.
N-Allyl-1-naphthylamine (2a);14 Typical Procedure
A mixture of 1-naphthylamine (1a (2 g, 13.9 mmol), allyl bromide
(1.01 g, 8.3 mmol), and dry K2CO3 (2.89 g, 20.9 mmol) in anhyd
acetone (50 mL) were refluxed for a period of 2 h. After cooling the
mixture was filtered and the solvent was removed in vacuo. The re-
sidual mass was extracted with EtOAc, washed with H2O and brine,
and dried (Na2SO4). Removal of EtOAc gave the crude product,
which was chromatographed (silica gel, 60–120 mesh, PE) to give
2-Allyl-N-tosyl-1-naphthylamine (6a)
Solid; yield: 92%; mp 134–135 °C.
IR (KBr): 3241, 1595, 1162 cm–1.
Synthesis 2010, No. 5, 863–869 © Thieme Stuttgart · New York

PAPER
Synthesis of Azepine- and Azocine-Annulated Heterocycles
867
1H NMR (400 MHz, CDCl3): d = 2.40 (s, 3 H, CH3), 3.26 (d, J = 6.4
Hz, 2 H, CHCH2), 4.93–4.99 (m, 1 H, =CHaHb), 5.06–5.09 (m, 1 H,
=CHaHb), 5.79–5.85 (m, 1 H, CHCH2), 6.41 (s, 1 H, NH), 7.20 (d,
J = 8.0 Hz, 2 H, ArH), 7.28–7.35 (m, 2 H, ArH), 7.39–7.43 (m, 1 H,
ArH), 7.54 (d, J = 8.4 Hz, 2 H, ArH), 7.74–7.77 (m, 2 H, ArH), 7.88
(d, J = 8.8 Hz, 1 H, ArH).
2-Allyl-N-but-3-enyl-N-tosyl-1-naphthylamine (7ab)
Gummy liquid; yield: 95%.
IR (neat): 2925, 2858, 1346, 1160 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.28–2.35 (m, 2 H, CH2), 2.42 (s,
3 H, CH3), 3.48 (d, J = 6.2 Hz, 2 H, =CHCH2), 3.62 (dt, J = 4.9 Hz,
J = 10.5 Hz, 1 H, NCHaHb), 3.72 (dt, J = 5.3 Hz, J = 10.5 Hz, 1 H,
NCHaHb), 4.93–4.97 (m, 2 H, =CH2), 5.07–5.13 (m, 2 H, =CH2),
5.48–5.72 (m, 1 H, =CH), 5.81–5.92 (m, 1 H, =CH), 7.21–7.25 (m,
3 H, ArH), 7.35–7.42 (m, 3 H, ArH), 7.62 (d, J = 7.8 Hz, 2 H, ArH),
7.76–7.79 (m, 2 H, ArH).
MS: m/z = 337 (M+).
Anal. Calcd for C20H19NO2S: C,71.19; H, 5.68; N, 4.15. Found: C,
71.38; H, 5.52; N, 4.01.
1-Allyl-N-tosyl-2-naphthylamine (6b)
Solid; yield: 87%; mp 116–117 °C.
MS: m/z = 391 (M+).
Anal. Calcd for C24H25NO2S: C, 73.62; H, 6.44; N, 3.58. Found: C,
73.88; H, 6.27; N, 3.66.
IR (KBr): 3288, 1595, 1155 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.36 (s, 3 H, CH3), 3.42–3.44 (m,
2 H, CHCH2), 4.79 (dd, J = 1.2, 17.2 Hz, 1 H, =CHaHb), 5.05 (dd,
J = 1.2, 10.4 Hz, 1 H, =CHaHb), 5.82–5.92 (m, 1 H, CH-CH2), 6.63
(s, 1 H, NH), 7.19 (d, J = 8.0 Hz, 2 H, ArH), 7.32 (d, J = 8.4 Hz, 1
H, ArH), 7.42–7.53 (m, 2 H, ArH), 7.62 (d, J = 9.2 Hz, 2 H, ArH),
7.73 (d, J = 9.2 Hz, 1 H, ArH), 7.80–7.85 (m, 2 H, ArH).
2-Allyl-N-propargyl-N-tosyl-1-naphthylamine (7ac)
Solid; yield: 93%; mp 94–95 °C.
IR (KBr): 2977, 2923, 1350, 1160 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.17 (s, 1 H, ≡CH), 2.44 (s, 3 H,
CH3), 3.52 (dd, J = 6.6 Hz, J = 15.6 Hz, 1 H, CHaHb), 3.63 (dd,
J = 6.3 Hz, J = 15.6 Hz, 1 H, CHaHb), 4.42 (dd, J = 2.0 Hz, J = 17.9
Hz, 1 H, NCHaHb), 4.62 (dd, J = 2.0 Hz, J = 17.9 Hz, 1 H,
NCHaHb), 5.11–5.15 (m, 2 H, =CH2), 5.90–5.97 (m, 1 H, =CH),
7.25 (d, J = 7.7 Hz, 2 H, ArH), 7.37–7.47 (m, 4 H, ArH), 7.68 (d,
J = 8.0 Hz, 2 H, ArH), 7.79 (d, J = 8.3 Hz, 2 H, ArH).
MS: m/z = 337 (M+).
Anal. Calcd for C20H19NO2S: C,71.19; H, 5.68; N, 4.15. Found: C,
71.35; H, 5.45; N, 4.09.
8-Allyl-7-(tosylamino)-4-methyl-2H-1-benzopyran-2-one (15b)
Solid; yield: 90%; mp 130–131 °C.
IR (KBr): 3379, 2926, 1727, 1614 cm–1.
MS: m/z = 375 (M+).
Anal. Calcd for C23H21NO2S: C, 73.57; H, 5.64; N, 3.73. Found: C,
73.86; H, 5.77; N, 3.89.
1H NMR (400 MHz, CDCl3): d = 2.36 (s, 3 H, CH3), 2.41 (s, 3 H,
CH3), 2.71 (dd, J = 3.2, 16.8 Hz, 1 H, CHCHaHb), 3.01–3.08 (m, 1
H, CHCHaHb), 4.11–4.14 (m, 1 H, =CHaHb), 4.27–4.30 (m, 1 H,
=CHaHb), 4.44–4.48 (m, 1 H, CHCH2), 6.15 (s, 1 H, H3coumarin), 7.20
(d, J = 8 Hz, 2 H, ArH), 7.48 (d, J = 8.4 Hz, 1 H, ArH), 7.59–7.64
(m, 3 H, ArH).
N,1-Diallyl-N-tosyl-2-naphthylamine (7ba)
Solid; yield; 95%; mp 102–103 °C.
IR (KBr): 2921, 1345, 1163 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.45 (s, 3 H, CH3), 3.91–4.02 (m,
2 H, =CHCH2), 4.12 (dd, J = 6 Hz, J = 16.0 Hz, 1 H, NCHaHb), 4.38
(dd, J = 6.1 Hz, J = 14.2 Hz, 1 H, NCHaHb), 4.90–5.07 (m, 4 H,
=CH2), 5.73–5.80 (m, 1 H, CH=CH2), 5.98–6.04 (m, 1 H,
CH=CH2), 6.72 (d, J = 8.7 Hz, 1 H, ArH), 7.28 (d, J = 7.9 Hz, 2 H,
ArH), 7.46–7.51 (m, 2 H, ArH), 7.59 (t, J = 8.4 Hz, 3 H, ArH), 7.78
(d, J = 8.4 Hz, 1 H, ArH), 8.08 (d, J = 8.4 Hz, 1 H, ArH).
MS: m/z = 369 (M+).
Anal. Calcd for C20H19NO4S: C, 65.02; H, 5.18; N, 3.79. Found: C,
64.91; H, 5.21; N, 3.85.
N,2-Diallyl-N-tosyl-1-naphthylamine (7aa); Typical Procedure
A mixture of 6a (0.50 g, 1.5 mmol), allyl bromide (0.27 g, 2.2
mmol), and dry K2CO3 (1.0 g) in acetone (50 mL) in the presence of
NaI13 (Finkelstein condition) was refluxed for 3 h. The mixture was
cooled and filtered and the solvent was removed. The residual mass
was extracted with CHCl3 (3 × 20 mL), washed with H2O (2 × 10
mL) followed by brine (5 mL) and dried (Na2SO4). Removal of
CHCl3 gave the crude product which was chromatographed (silica
gel, 60–120 mesh, 3% EtOAc–PE) to give 7aa as a solid; yield:
94%; mp 65–66 °C. Accordingly, compounds 7ab, 7ac, 7ba, 7bb,
13b, and 16b were prepared.
MS: m/z = 377 (M+).
Anal. Calcd for C23H23NO2S: C, 73.18; H, 6.14; N, 3.71. Found: C,
72.98; H, 5.89; N, 3.57.
1-Allyl-N-but-3-enyl-N-tosyl-2-naphthylamine (7bb)
Solid; yield: 95%; mp 95–96 °C.
IR (KBr): 2925, 2857, 1344, 1160 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.08–2.11 (m, 1 H, NCH2CHaHb),
2.26–2.29 (m, 1 H, NCH2CHaHb), 2.44 (s, 3 H, CH3), 3.33–3.41 (m,
1 H, NCHaHb), 3.80–3.88 (m, 1 H, NCHaHb), 3.96 (dd, J = 4.5 Hz,
J = 16.5 Hz, 1 H, CHaHb), 4.08 (dd, J = 5.9 Hz, J = 16.2 Hz, 1 H,
CHaHb), 4.96–5.08 (m, 4 H, =CH2), 5.63–5.69 (m, 1 H, CH=CH2),
5.99–6.06 (m, 1 H, CH=CH2), 6.74 (d, J = 8.7 Hz, 1 H, ArH), 7.26
(t, J = 7.8 Hz, 2 H, ArH), 7.47–7.53 (m, 2 H, ArH), 7.56–7.61 (m, 3
H, ArH), 7.79 (d, J = 8.8 Hz, 1 H, ArH), 8.10 (d, J = 8.4 Hz, 1 H,
ArH).
IR (KBr: 2923, 2854, 1347, 1162 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.44 (s, 3 H, CH3), 3.52 (d, J = 6.4
Hz, 2 H, =CHCH2), 4.13 (dd, J = 7.6 Hz, J = 14.6 Hz, 1 H, NCHaH-
bCH=), 4.41 (dd, J = 6.3 Hz, J = 14.6 Hz, 1 H, NCHaHbCH=), 4.88–
4.97 (m, 2 H, =CH2), 5.11–5.14 (m, 2 H, =CH2), 5.88–5.93 (m, 2 H,
=CH), 7.22–7.26 (m, 2 H, ArH), 7.36–7.42 (m, 4 H, ArH), 7.66 (d,
J = 7.9 Hz, 2 H, ArH), 7.78 (t, J = 8.3 Hz, 2 H, ArH).
13C NMR (75 MHz, CDCl3): d = 21.5, 36.5, 54.7, 116.7, 119.2,
124.2, 125.4, 126.2, 127.6, 127.8, 128.1, 128.7, 129.5, 132.0, 132.9,
133.0, 133.5, 136.9, 137.7, 139.4, 143.4.
MS: m/z = 391 (M+).
Anal. Calcd for C24H25NO2S: C, 73.62; H, 6.44; N, 3.58. Found: C,
73.45; H, 6.59; N, 3.81.
HRMS: m/z [M + H]+ calcd for C23H24NO2S: 378.1522; found:
378.1484.
5-Allyl-6-[allyl(methyl)amino]-2H-1-benzopyran-2-one (13b)
Gummy liquid; yield: 75%.
IR (neat): 1732, 1120 cm–1.
Anal. Calcd for C23H23NO2S: C, 73.18; H, 6.14; N, 3.71. Found: C,
73.01; H, 5.87; N, 3.66.
Synthesis 2010, No. 5, 863–869 © Thieme Stuttgart · New York

868
K. C. Majumdar et al.
PAPER
1H NMR (400 MHz, CDCl3): d = 2.57 (s, 3 H, NCH3), 3.38 (d, J = 6
Hz, 2 H, CH2), 3.73–3.75 (m, 2 H, NCH2), 4.76 (dd, J = 1.6 Hz,
J = 15.6 Hz, 1 H, =CH2), 4.79–5.16 (m, 3 H, =CH2), 5.69–5.79 (m,
1 H, CH=CH2), 5.91–6.01 (m, 1 H, CH=CH2), 6.32 (d, J = 10 Hz, 1
H, H3coumarin), 7.13 (d, J = 9.2 Hz, 1 H, ArH), 7.28 (d, J = 8.8 Hz, 1
H, ArH), 7.80 (d, J = 10 Hz, 1 H, H4coumarin).
ArH), 7.34–7.39 (m, 2 H, ArH), 7.43 (d, J = 8.4 Hz, 1 H, ArH), 7.66
(d, J = 7.8 Hz, 2 H, ArH), 7.78 (t, J = 9.3 Hz, 2 H, ArH).
13C NMR (75 MHz, CDCl3): d = 21.5, 27.3, 34.4, 49.2, 123.5,
125.3, 126.3, 126.5, 127.5, 127.7, 128.1, 129.1, 129.5, 132.5, 132.6,
133.2, 133.6, 138.6, 142.5, 143.2.
MS: m/z = 363 (M+).
MS: m/z = 255 (M+).
Anal. Calcd for C22H21NO2S: C, 72.70; H, 5.82; N, 3.85. Found: C,
72.51; H, 5.67; N, 4.11.
Anal. Calcd for C16H17NO2: C, 75.27; H, 6.71; N, 5.49. Found: C,
75.39; H, 6.57; N, 5.33.
1-Tosyl-3-vinyl-2,5-dihydro-1H-naphtho[1,2-b]azepine (10ac)
8-Allyl-7-[allyl(tosyl)amino]-4-methyl-2H-1-benzopyran-2-one
(16b)
Gummy liquid; yield: 94%.
Solid; yield: 61%; mp 145–146 °C.
IR (KBr): 2922, 2852, 1351, 1159 cm–1.
1H NMR (300 MHz, CDCl3): d = 2.43 (s, 3 H, CH3.), 2.94 (dd,
J = 8.7 Hz, J = 18.0 Hz, 1 H, CHaHb), 3.27 (dd, J = 8.2 Hz, J = 18.0
Hz, 1 H, CHaHb), 4.02 (d, J = 18.0 Hz, 1 H, NCHaHb), 4.94–5.09
(m, 2 H, =CH2), 5.19 (d, J = 18.0 Hz, 1 H, NCHaHb), 5.68 (d, J = 8.4
Hz, 1 H, =CH), 6.17–6.27 (m, 1 H, =CH), 7.17 (d, J = 8.4 Hz, 1 H,
ArH), 7.19–7.23 (m, 2 H, ArH), 7.49 (t, J = 8.4 Hz, J = 8.1 Hz, 2 H,
two triplets overlap, ArH), 7.66 (d, J = 7.8 Hz, 2 H, ArH), 7.75 (d,
J = 8.4 Hz, 1 H, ArH), 7.82 (d, J = 7.8 Hz, 1 H, ArH), 8.11 (d,
J = 8.1 Hz, 1 H, ArH).
IR (neat): 2920, 2854, 1734, 1121 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.40 (s, 3 H, CH3), 2.45 (s, 3 H,
CH3), 3.65 (d, J = 6.5 Hz, 2 H, =CHCH2), 4.04 (dd, J = 7.4 Hz,
J = 14.5 Hz, 1 H, NCHaHb), 4.21 (dd, J = 6.8 Hz, J = 14.5 Hz, 1 H,
NCHaHb), 4.91–5.07 (m, 4 H, =CH2), 5.69–5.76 (m, 1 H, CH=CH2),
5.93–6.00 (m, 1 H, CH=CH2), 6.29 (s, 1 H, H3coumarin), 6.71 (d,
J = 8.6 Hz, 1 H, ArH), 7.30 (d, J = 7.9 Hz, 2 H, ArH), 7.35 (d,
J = 8.3 Hz, 1 H, ArH), 7.60 (d, J = 7.9 Hz, 2 H, ArH).
MS: m/z = 409 (M+).
13C NMR (100 MHz, CDCl3): d = 21.7, 36.5, 47.9, 117.2, 123.9,
125.3, 125.8, 126.3, 127.3, 127.6, 127.7, 129.1, 129.4, 129.5, 130.4,
133.1, 133.7, 136.3, 136.5, 140.9, 145.3.
Anal. Calcd for C23H23NO4S: C, 67.46; H, 5.66; N, 3.42. Found: C,
67.69; H, 5.83; N, 3.61.
MS: m/z = 375 (M+).
1-Tosyl-2,5-dihydro-1H-naphtho[1,2-b]azepine (10aa); Typical
Procedure
Anal. Calcd for C23H21NO2S: C,73.57; H, 5.64; N, 3.73. Found: C,
73.41; H, 5.45; N, 3.99.
Compound 7aa (100 mg, 0.26 mmol) was taken up in anhyd CH2Cl2
(5 mL) in a small flask and the mixture was degassed for 5 min with
dry N2. Grubbs I (10.7 mg, 5 mol%) was also dissolved in anhyd
CH2Cl2 and was degassed for 5 min. The catalyst soln was injected
to the soln of compound 7aa and the mixture was stirred at 25 °C
for 30 min. The solvent was removed under reduced pressure to give
a dark mass that after column chromatography (silica gel, 4%
EtOAc–PE) gave 10aa as a solid; yield: 96%; mp 154–155 °C. Oth-
er substrates were similarly treated to give the products, except in
case of substrate 7bc where the solvent for the reaction was toluene
and the mixture was refluxed for nearly 10 h.
5-Tosyl-4,5-dihydro-1H-naphtho[2,1-b]azepine (10ba)
Solid; yield: 95%; mp 158–159 °C.
IR (KBr): 2923, 2851, 1339, 1156 cm–1.
1H NMR (300 MHz, CDCl3): d = 2.43 (s, 3 H, CH3), 3.50 (br s, 2 H,
CH2), 4.41 (br s, 2 H, NCH2), 5.50 (d, J = 11.1 Hz, 1 H, =CHaHb),
5.81–5.84 (m, 1 H, =CHaHb), 7.27 (d, J = 6.3 Hz, 2 H, ArH), 7.40
(d, J = 8.7 Hz, 1 H, ArH), 7.48–7.50 (m, 2 H, ArH), 7.68–7.71 (m,
3 H, ArH), 7.84 (dd, J = 2.3 Hz, J = 8.1 Hz, 1 H, ArH), 8.02 (d,
J = 7.2 Hz, 1 H, ArH).
13C NMR (100 MHz, CDCl3): d = 21.6, 24.6, 48.8, 123.8, 125.0,
126.1, 126.3, 126.7, 127.0, 127.1, 127.6, 128.7, 129.6, 131.2, 133.3,
136.4, 138.0, 138.8, 143.3.
IR (KBr): 2922, 2851, 1334, 1157 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.36 (s, 3 H, CH3), 2.77 (dd, J = 8
Hz, J = 17.6 Hz, 1 H, CHaHb), 3.14 (d, J = 17.6 Hz, 1 H, CHaHb),
3.84–3.89 (m, 1 H, NCHaHb), 4.84–4.89 (m, 1 H, NCHaHb), 5.37–
5.42 (m, 1 H, =CHa), 5.52–5.56 (m, 1 H, =CHb), 7.10 (d, J = 8.4 Hz,
1 H, ArH), 7.17 (d, J = 7.6 Hz, 2 H, ArH), 7.35–7.43 (m, 2 H, ArH),
7.61 (d, J = 8.4 Hz, 2 H, ArH), 7.66 (d, J = 8.4 Hz, 1 H, ArH), 7.75
(d, J = 6.8 Hz, 1 H, ArH), 7.99 (d, J = 8.2 Hz, 1 H, ArH).
MS: m/z = 349 (M+).
Anal. Calcd for C21H19NO2S: C,72.18; H, 5.48; N, 4.01. Found: C,
72.31; H, 5.27; N, 3.87.
6-Tosyl-1,4,5,6-dihydronaphtho[2,1-b]azocine (10bb)
13C NMR (75 MHz, CDCl3): d = 21.5, 32.8, 48.4, 124.0, 125.0,
125.7, 125.9, 126.7, 127.4, 127.5, 127.7, 128.9, 129.4, 132.5, 133.6,
134.5, 138.9, 139.5, 143.3.
Solid; yield: 89%; mp 112–113 °C.
IR (KBr): 2922, 2852, 1345, 1158 cm–1.
1H NMR (300 MHz, CDCl3): d = 2.20–2.27 (m, 1 H, CHaHb), 2.44
(s, 3 H, CH3), 2.78–2.85 (m, 2 H, CH2), 3.62–3.69 (m, 1 H, CHaHb),
3.86–3.93 (m, 1 H, NCHaHb), 4.37–4.41 (m, 1 H, NCHaHb), 5.55–
5.62 (m, 1 H, =CH), 6.02–6.11 (m, 1 H, =CH), 7.00 (d, J = 8.7 Hz,
1 H, ArH), 7.30 (d, J = 7.8 Hz, 2 H, ArH), 7.46–7.62 (m, 3 H, ArH),
7.73 (d, J = 8.1 Hz, 2 H, ArH), 7.80 (d, J = 7.8 Hz, 1 H, ArH), 8.13
(d, J = 8.4 Hz, 1 H, ArH).
13C NMR (100 MHz, CDCl3): d = 21.6, 27.6, 29.3, 51.6, 124.7,
126.3, 126.5, 126.8, 127.4, 127.5, 128.3, 128.5, 129.7, 131.7, 132.4,
133.4, 136.0, 138.4, 140.9, 143.4.
HRMS: m/z [M + Na]+ calcd for C21H19NNaO2S: 372.1034; found:
372.1034.
Anal. Calcd for C21H19NO2S: C, 72.18; H, 5.48; N, 4.01. Found: C,
72.30; H, 5.71; N, 3.85.
1-Tosyl-1,2,3,6-dihydronaphtho[1,2-b]azocine (10ab)
Solid; yield: 94%; mp 144–145 °C.
IR (KBr): 2930, 2868, 1342, 1157 cm–1.
1H NMR (300 MHz, CDCl3): d = 2.03–2.13 (m, 1 H, CHaHb), 2.43
(s, 3 H, CH3), 2.52–2.59 (m, 1 H, CHaHb), 3.05 (dd, J = 6.9 Hz,
J = 14.4 Hz, 2 H, =CHCH2), 3.88 (dd, J = 6.9 Hz, J = 14.7 Hz, 1 H,
N-CHaHb), 4.36 (dd, J = 7.5 Hz, J = 14.7 Hz, 1 H, NCHaHb), 5.46–
5.55 (m, 1 H, =CH), 5.75–5.83 (m, 1 H, =CH), 7.17–7.26 (m, 3 H,
MS: m/z = 363 (M+).
Anal. Calcd for C22H21NO2S: C, 72.70; H, 5.82; N, 3.85. Found: C,
72.48; H, 5.89; N, 3.99.
Synthesis 2010, No. 5, 863–869 © Thieme Stuttgart · New York

PAPER
Synthesis of Azepine- and Azocine-Annulated Heterocycles
869
7-Methyl-8,11-dihydro[1]benzopyrano[6,5-b]azepin-3(7H)-one
(17b)
Gummy liquid; yield: 35%.
IR (neat): 1734, 1122 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.82 (s, 3 H, NCH3), 3.50 (br s, 2
H, CH2), 3.65 (d, J = 5.3 Hz, 2 H, NCH2), 5.42 (d, J = 11 Hz, 1 H,
=CH), 5.81–5.87 (m, 1 H, =CH), 6.39 (d, J = 9.8 Hz, 1 H,
H3coumarin), 7.18 (d, J = 8.8 Hz, 1 H, ArH), 7.26 (d, J = 9 Hz, 1 H,
ArH), 7.98 (d, J = 9.8 Hz, 1 H, H4coumarin).
13C NMR (100 MHz, CDCl3): d = 29.7, 43.4, 57.7, 114.7, 115.6,
116.1, 122.3, 124.3, 128.7, 136.2, 140.4, 147.8, 150.1, 160.8.
(5) For recent review on medium-sized heterocycles, see:
(a) Majumdar, K. C.; Chattopadhyay, B. Curr. Org. Chem.
2009, 13, 731. (b) Chattopadhyay, S. K.; Karmakar, S.;
Biswas, T.; Majumdar, K. C.; Rahman, H.; Roy, B.
Tetrahedron 2007, 63, 3919. (c) Majumdar, K. C.;
Chattopadhyay, B.; Ansary, I. Can. J. Chem. 2009, 87, 472.
(6) (a) Brennan, P.; Whitlock, G. A.; Ho, D. K. H.; Conlon, K.;
McMurray, G. Bioorg. Med. Chem. Lett. 2009, 19, 4999.
(b) Neelamkavil, S. F.; Boyle, C. D.; Chackalamannil, S.;
Greenlee, W. J. Bioorg. Med. Chem. Lett. 2009, 19, 4563.
(c) Coleman, R. S.; Campbell, E. L.; Carper, D. J. Org. Lett.
2009, 11, 2133. (d) de la Fuente, M. C.; Dominguez, D.
Tetrahedron 2009, 65, 3653. (e) Raw, S. A.; Taylor, R. J. K.
Tetrahedron Lett. 2004, 45, 8607.
MS: m/z = 227 (M+).
Anal. Calcd for C14H13NO2: C, 73.99; H, 5.77; N, 6.16. Found: C,
74.16; H, 5.56; N, 5.98.
(7) (a) Akhter, L.; Brown, R. T.; Moorcroft, D. Tetrahedron
Lett. 1978, 19, 4137. (b) Valencia, E.; Fajardo, V.; Freyer,
A. J.; Shamma, M. Tetrahedron Lett. 1985, 26, 993.
(c) Sakai, R.; Higa, T.; Jeffod, C. W.; Bernardinelli, G.
J. Am. Chem. Soc. 1986, 108, 6404. (d) Trindade, A. C. L.
B.; dos Santos, D. C.; Gil, L.; Marazano, C.; de Freitas Gil,
R. P. Eur. J. Org. Chem. 2005, 1052.
4-Methyl-7-tosyl-8,11-dihydro[1]benzopyrano[7,8-b]azepin-
2(7H)-one (18b)
Solid; yield: 89%; mp 130–131 °C.
IR (KBr): 2923, 2853, 1735, 1159 cm–1.
(8) Evans, P. A.; Holmes, A. B. Tetrahedron 1991, 47, 9131.
(9) Trindade, A. C. L. B.; dos Santos, D. C.; Gil, L.; Marazano,
C.; Gil, S. P. de F. Eur. J. Org. Chem. 2005, 1052.
(10) (a) Majumdar, K. C.; Chattopadhyay, B. Synlett 2008, 979.
(b) Majumdar, K. C.; Chattopadhyay, B.; Ray, K.
Tetrahedron Lett. 2007, 48, 7633. (c) Majumdar, K. C.;
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) Majumdar,
K. C.; Chattopadhyay, B.; Sinha, B. Synthesis 2008, 3857.
(f) Majumdar, K. C.; Mondal, S. Synlett 2008, 2851.
(g) Majumdar, K. C.; Chattopadhyay, B. Synthesis 2009,
2385.
1H NMR (300 MHz, CDCl3): d = 2.43 (s, 6 H, CH3), 3.19 (br s, 2 H,
CH2), 4.39 (br s, 2 H, NCH2), 5.47 (d, J = 11.1 Hz, 1 H, =CH), 5.51–
5.69 (m, 1 H, =CH), 6.29 (s, 1 H, H3coumarin), 7.27–7.33 (m, 2 H,
ArH), 7.36 (d, J = 8.4 Hz, 1 H, ArH), 7.49 (d, J = 8.4 Hz, 1 H, ArH),
7.64 (d, J = 7.8 Hz, 2 H, ArH).
13C NMR (100 MHz, CDCl3): d = 18.9, 21.5, 32.9, 48.9, 112.5,
113.0, 118.2, 119.1, 125.0, 126.8, 127.0, 129.4, 129.8, 134.9, 144.4,
145.2, 150.4, 152.7, 160.6.
MS: m/z = 381 (M+).
Anal. Calcd for C21H19NO4S: C, 66.12; H, 5.02; N, 3.67. Found: C,
66.29; H, 5.27; N, 3.44.
(11) Majumdar, K. C.; Chattopadhyay, B.; Chakravorty, S.
Synthesis 2009, 674.
Acknowledgment
(12) (a) Fu, G. C.; Grubbs, R. H. J. Am. Chem. Soc. 1992, 114,
5426. (b) Fu, G. C.; Nguyen, S. T.; Grubbs, R. H. J. Am.
Chem. Soc. 1993, 115, 9856. (c) Herisson, J.-L.; Chauvin,
Y. Makromol. Chem. 1971, 141, 161. (d) Grubbs, R. H.;
Carr, D. D.; Hoppin, C.; Burk, P. L. J. Am. Chem. Soc. 1976,
98, 3478. (e) Lloyd-Jones, G. C.; Margue, R. G.; de Vries, J.
G. Angew. Chem. Int. Ed. 2005, 44, 7442. (f) Majumdar, K.
C.; Rahaman, H.; Islam, R.; Roy, B. Org. Biomol. Chem.
2006, 4, 2393.
We thank the CSIR (New Delhi) for financial assistance and three
of us (S.S., B.C. and R.N.) are grateful to the CSIR (New Delhi) for
our fellowships.
References
(1) For some recent reviews on Claisen rearrangement, see:
(a) Majumdar, K. C.; Bhattacharyya, T.; Chattopadhyay, B.;
Sinha, B. Synthesis 2009, 2117. (b) Majumdar, K. C.; Alam,
S.; Chattopadhyay, B. Tetrahedron 2008, 64, 597.
(c) Castro, A. M. Chem. Rev. 2004, 104, 2939.
(d) Nubbemeyer, U. Synthesis 2003, 961.
(13) (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.
(14) Von Schmid, M.; Hansen, H.-J.; Schmid, H. Helv. Chim.
Acta 1973, 56, 105.
(15) Majumdar, K. C.; Chakravorty, S.; Shyam, P. K.; Taher, A.
Synthesis 2009, 403.
(16) Reddy, A. R.; Prasad, D. V.; Darbarwar, M. J. Photochem.
1986, 32, 69.
(2) Alajarín, M.; Vidal, A.; Ortín, M.-M. Tetrahedron 2005, 61,
7613.
(3) Marcinkiewicz, S.; Green, J.; Mamalis, P. Tetrahedron
1961, 14, 208.
(4) Inada, S.; Kurata, R.-i. Bull. Chem. Soc. Jpn. 1981, 54, 1581.
Synthesis 2010, No. 5, 863–869 © Thieme Stuttgart · New York