A new route to pyranocoumarins and their benzannulated derivatives

Article abstract of DOI:10.1055/s-0034-1379141

A new protocol based on sequential applications of three atom-economic processes viz. Claisen rearrangement, olefin isomerisation, and ring-closing diene metathesis has been developed to access a range of linear and angularly fused pyranocoumarin derivatives. Incorporation of enyne (in place of diene) metathesis and Diels-Alder reaction in the sequence has allowed the corresponding benzannulated derivatives to be prepared in good yields.

Full text of DOI:10.1055/s-0034-1379141

PAPER
▌3331
paper
A New Route to Pyranocoumarins and Their Benzannulated Derivatives
Synthesis of Pyranocoumarins and Benzopyranocoumarins
Shital K. Chattopadhyay,* Poulomi Mondal, Debalina Ghosh
Department of Chemistry, University of Kalyani, Kalyani-741235, West Bengal, India
Fax +91(33)25828282; E-mail: skchatto@yahoo.com
Received: 29.06.2014; Accepted after revision: 20.08.2014
ophile followed by aromatisation of the cycloadduct,
would constitute a general synthesis of benzannulated
pyranocoumarin derivatives of the type IX.
Abstract: A new protocol based on sequential applications of three
atom-economic processes viz. Claisen rearrangement, olefin isom-
erisation, and ring-closing diene metathesis has been developed to
access a range of linear and angularly fused pyranocoumarin deriv-
atives. Incorporation of enyne (in place of diene) metathesis and
Diels–Alder reaction in the sequence has allowed the corresponding
benzannulated derivatives to be prepared in good yields.
O
O
O
O
O
O
Key words: heterocycle, metathesis, rearrangement, Diels–Alder
reaction, isomerization
xanthetin (2)
O
i-Bu
OAc
O
OCam
suksdorfin (1)
Coumarins are widely distributed in nature and are found
in all parts of plants.1 Several heteroannulated coumarins
of both the linear and angular type display interesting bi-
ological activities.2 Among them, pyranocoumarins are of
special importance because of their broad spectrum of bi-
ological activities.3–5 Compounds 1–3 (Figure 1) are good
examples in this regard, and a great number of methodol-
ogies have been developed to access such targets.
Amongst them, Trost’s palladium-catalysed addition of
activated phenols to alkynoates,6 Nicolaou’s Knoevenagel
transesterification on solid phase,7 Liu’s gold-catalysed
annulation,8 Yadav’s domino Knoevenagel/hetero-Diels–
Alder protocol,9 and multi-component protocols10 are no-
table, among others.11 Moreover, fusion of a benzene ring
onto pyranocoumarins has been reported to impart signif-
icant changes to the biological and material properties.12
Therefore, the synthesis of benzo-fused pyranocoumarins
continue to be developed.13 Nevertheless, the develop-
ment of a common route to angular- and linearly fused
pyranocoumarins and their benzo-fused analogues re-
mains important. Several years ago, we reported a se-
quence of Claisen rearrangement and ring-closing
metathesis (RCM) reaction to prepare various medium-
ring-sized oxacycle-fused coumarin derivatives I–IV
(Scheme 1).14 The methodology has found application in
the preparation of related systems.15 We realised that in-
corporation of an isomerisation step in the sequence
would lead to a general and simple synthesis of pyrano-
coumarin derivatives in a similar fashion; that is, the con-
version II → V → VI.
OCam
O
O
O
DCK (3)
Figure 1 Representative pyran ring fused biologically active couma-
rins; Cam = camphanoyl
Claisen
rearrangement
O
OH
O
O-alkylation
coum-
arin
coum-
arin
n
coum-
arin
III
II
I
RCM
O
O
OH
O-allylation
RCM
n
coum-
arin
coum-
arin
coum-
arin
VI
IV
V
CO2R
O-propargylation
O
O
O
CO2R
coum-
arin
RCEYM
coum-
arin
coum-
arin
aromati-
sation
RO2C
CO2R
VII
VIII
IX
Scheme 1 Synthetic plan
Additionally, the propargyl ether VII, derived from the
isomerised phenol V, on ring-closing enyne metathesis
(RCEYM) may lead to the formation of dienes of type
VIII, which, on Diels–Alder reaction with a suitable dien-
Our synthesis started with the Claisen rearrangement of
allyl ether 4 (Scheme 2), obtained by O-allylation of 4-
methyl-7-hydroxycoumarin. Claisen rearrangement of 4
was previously carried out16 by either heating neat or to
reflux in N,N-diethylaniline. We found that the rearrange-
ment also proceeded well upon heating diphenyl ether to
reflux, and product isolation was less tedious under the
developed conditions. Moreover, the rearranged phenol 5
SYNTHESIS 2014, 46, 3331–3340
Advanced online publication: 15.09.2014
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
DOI: 10.1055/s-0034-1379141; Art ID: ss-2014-t0401-op
© Georg Thieme Verlag Stuttgart · New York

3332
S. K. Chattopadhyay et al.
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many isomerisation/RCM sequences for the synthesis of
carbocyclic and heterocyclic systems.18 We were pleased
to observe that when a solution of 5 in anhydrous benzene
was heated to reflux in the presence of 2 mol% of the said
ruthenium catalyst for 24 hours under a nitrogen atmo-
sphere, the expected isomerised product 6 was formed in
83% yield and as a single isomer. The isomer was identi-
fied as E from the coupling constant in the NMR spec-
trum, in which the required proton appeared at δ =
6.62 ppm (d, J = 16 Hz, 1 H). Subsequent O-allylation of
the isomerised product 6 with allyl bromide afforded 7 in
75% yield. Ring-closing metathesis of 7 with Grubbs
ii
i
HO
O
O
O
O
O
HO
O
O
4 (82%)
5 (80%)
iii
iv
HO
v
O
O
O
O
O
O
O
O
first-generation catalyst
9
[bis(tricyclohexylphos-
phine)benzylidine-ruthenium(II)] in benzene heated to
reflux proceeded well to provide the desired pyranocou-
marin 10 in 85% yield. Similarly, O-allylation of 6 with
methallyl chloride afforded the O-tethered diene 8. How-
ever, RCM of the latter with catalyst 9 was problematic.
Switching to the Grubbs second-generation catalyst 11
[benzylidene [1,3-bis(2,4,6-trimethylphenyl)-2-imidazo-
lidinylidene]dichloro (tricyclohexylphosphine)rutheni-
um] resolved the problem and the desired product 12 was
obtained in a overall yield of 35% over a linear sequence
of five steps.
R
R
10, R = H (85%)
12, R = Me (84%)
7, R = H (75%)
8, R = Me (77%)
6 (83%)
Scheme 2 Reagents and conditions: (i) allyl bromide, acetone,
K2CO3, reflux; (ii) diphenyl ether, reflux; (iii) RuClH(CO)(PPh3)3 (2
mol%), benzene, reflux; (iv) allyl bromide/3-chloro-2-methyl-pro-
pene, K2CO3, acetone, reflux; (v) catalyst 9/catalyst 11 (5 mol%), an-
hydrous benzene, reflux.
was obtained as the only regioisomer in 80% yield.
[Ru(CO)HCl(PPh3)3]17 is known to catalyse the isomeri-
sation of terminal double bonds and has found use in
iii
ii
RO
i
O
O
HO
O
O
HO
O
O
16 (83%)
13, R = H
15, R = CH2CH=CH2 (78%)
17 (85%)
R
v
iv
O
O
O
O
O
O
R
18, R = H (74%)
19, R = Me (82%)
20, R = H (87%)
21, R = Me (83%)
RO
HO
HO
iii
ii
O
O
O
O
O
O
24 (76%)
14, R = H
22, R = CH2CH=CH2 (84%)
23 (79%)
i
R
R
O
O
v
iv
O
O
O
O
25, R = H (80%)
26, R = Me (78%)
27, R = H (82%)
28, R = Me (81%)
Scheme 3 Reagents and conditions: (i) allyl bromide, acetone, K2CO3, reflux; (ii) diphenyl ether, reflux; (iii) RuClH(CO)(PPh3)3 (2 mol%),
benzene, reflux; (iv) allyl bromide/3-chloro-2-methyl-propene, K2CO3, acetone, reflux; (v) catalyst 9/11 (5 mol%), anhydrous benzene, reflux.
Synthesis 2014, 46, 3331–3340
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Synthesis of Pyranocoumarins and Benzopyranocoumarins
3333
With optimised conditions in hand, we then turned our at- step.20 We,21 and others22 have reported a sequential
tention to study the scope and generality of the methodol- Claisen rearrangement/RCEYM/Diels–Alder reaction as
ogy. Coumarin derivatives with angular- and linearly a cascade route to oxepin ring-fused heterocycles. We be-
fused heterocyclic motifs have attracted the attention of came interested in including the isomerisation step in this
both chemists and biologists. We therefore employed the sequence to prepare benzannulated pyranocoumarin de-
sequence of reactions on two other easily obtainable hy- rivatives. Thus, the phenolic OH group in 6 was reacted
droxycoumarin derivatives: 4,8-dimethyl-7-hydroxycou- with propargyl bromide under conventional conditions to
marin (13) and 6-hydroxycoumarin (14). Thus, O-allyl obtain the O-tethered enyne derivative 29 (Scheme 4).
ether 15, prepared by O-allylation of 13, underwent clean RCEYM reactions of olefins other than terminal olefins
rearrangement upon heating to reflux in diphenyl ether to have been less well documented compared with those of
provide the known rearranged phenol 16 (Scheme 3). terminal olefins. In the few instances studied, interesting
Isomerisation of the latter with [Ru(CO)HCl(PPh3)3] pro- mechanistic and stereochemical observations have been
ceeded smoothly and produced the isomerised olefin 17 made.23 However, heteroatom-tethered enynes have been
but as a mixture of E/Z-isomers in a ratio of approximately reported to show poor selectivity.24 It was observed that
3:1 in favour of the E-isomer. The E-isomer could be sep- RCEYM of 29 proceeded sluggishly in the presence of the
arated with difficulty, for characterisation. However, for second generation catalyst 11 under the optimised condi-
synthetic purposes, the mixture was carried through be- tions to provide diene 30 (70%), mostly as the E-isomer
cause the isomeric identity was lost in the subsequent but contaminated with the Z-isomer (5–10%), which
RCM reaction. Repetition of the sequences detailed for could not be separated. Similarly, enyne derivatives 31
the conversion 7→10 and 8→12 on 17; i.e., further O-al- and 33 provided the corresponding dienes 32 and 34 in
lylation leading to the dienes 18/19 followed by their similar yields and stereochemical identity.
RCM with catalysts 9 or 11, provided the linearly fused
pyranocoumarin derivatives 20 and 21 in good overall
Mechanistically, the reaction may follow either the ‘ene-
then-yne’ or ‘yne-then-ene’ pathways25 (Scheme 5). In
yields of 35.4 and 37.5%, respectively. Similarly, starting
path A, the ruthenium carbene complex may coordinate
with 6-allyloxycoumarin (22) the isomerised phenol 24
with the alkyne part of the substrate 29 to form a new in-
was prepared (mostly E) and converted into the angularly
termediate complex 35, which, on subsequent cyclisation,
fused pyranocoumarin derivatives 27 and 28 in compara-
will produce the product 30. In this case, the reaction will
be expected to exhibit stereoselectivity similar to that of a
ble yields.
Ruthenium-catalysed ring-closing enyne metathesis cross-enyne metathesis reaction.
(RCEYM) has become a powerful tool with which to con-
On the other hand, the carbene complex 36 will result if
the reaction occurs at the ene site (pathway B). The com-
plex 36 will cyclise to produce a new complex 37, which
struct heterocyclic derivatives.19 The efficacy of the pro-
cess has been increased by combining other synthetic
transformations either before or after the metathesis
Br
catalyst 11
6
benzene, reflux
O
O
O
O
O
O
Me2CO, K2CO3
reflux
29 (79%)
30 (70%)
Br
catalyst 11
17
benzene, reflux
O
O
O
Me2CO, K2CO3
reflux
O
O
O
32 (72%)
31 (65%)
Br
O
O
catalyst 11
24
benzene, reflux
Me2CO, K2CO3
reflux
O
O
O
O
34 (75%)
33 (78%)
Scheme 4 RCEYM of O-tethered enyne derivatives
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2014, 46, 3331–3340

3334
S. K. Chattopadhyay et al.
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tained as the major (90–95%) isomer, which has little pre-
cedence.
Having access to dienes 30, 32, and 34, we then focused
our attention on their Diels–Alder cycloaddition reaction
with a suitable dienophile, which would secure formation
of a benzene ring in our projected benzannulation reac-
tion. We observed that prolonged heating of diene 30 with
diethyl acetylenedicarboxylate (Scheme 6) in toluene at
reflux led to the formation of a single product in 71%
yield, which was identified as 39. The formation of the lat-
ter may be explained by initial formation of the cycload-
duct 38 (not isolated) followed by its aerial oxidation in
situ.
O
O
O
O
O
O
A
Ru
30
29
B
35
Ru
O
O
O
O
O
O
O
O
O
Similarly, diene 32, on reaction with dimethyl acety-
lenedicarboxylate under analogous conditions, provided
benzannulated product 41 in comparable yield. The same
sequence of reactions was then repeated with diene 34 to
obtain the angularly fused benzopyranocoumarin deriva-
tive 43. It is interesting to note that the angular- and lin-
early fused pyranocoumarin formed with similar facility
and rate.
Ru
36
Ru
37
30
Scheme 5 Representation of plausible catalytic pathways: ‘yne-
then-ene’ pathway (A) and ‘ene-then-yne’ pathway (B)
In conclusion, we have demonstrated that combined
Claisen rearrangement, olefin isomerisation and olefin
metathesis is an efficacious strategy for the preparation of
several linearly and angularly architectured pyranocou-
marin derivatives. This consecutive ruthenium-catalysed
may then react with the olefin part of a second substrate
molecule, leading to the 1,3-diene product 30. The stereo-
selectivity in this case will be similar to that of a cross-ene
metathesis. It is interesting to note that diene 30 is ob-
EtO2C
CO2Et
O
O
O
30
O
O
O
toluene, reflux
CO2Et
CO2Et
CO2Et
CO2Et
38 (not isolated)
39 (71%)
CO2Me
CO2Me
CO2Me
CO2Me
MeO2C
toluene, reflux
CO2Me
32
O
O
O
O
O
O
41 (61%)
40 (not isolated)
CO2Et
CO2Et
CO2Et
CO2Et
EtO2C
toluene, reflux
CO2Et
34
O
O
O
O
O
O
43 (75%)
42 (not isolated)
Scheme 6 One-pot Diels–Alder cycloaddition and aromatisation
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Synthesis of Pyranocoumarins and Benzopyranocoumarins
3335
1H NMR (400 MHz, CDCl3): δ = 7.40 (d, J = 8.8 Hz, 1 H), 6.82 (d,
J = 8.8 Hz, 1 H), 6.13 (s, 1 H), 6.12–6.03 (m, 1 H), 5.45 (td, J = 1.2,
19.2 Hz, 1 H), 5.32 (td, J = 1.2, 10.8 Hz, 1 H), 4.65–4.64 (m, 2 H),
2.39 (s, 3 H), 2.33 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 161.4, 159.2, 152.8, 152.5, 132.7,
122.4, 117.5, 114.1, 113.6, 111.7, 107.8, 69.1, 18.6, 8.2.
reaction protocol has been extended to the preparation of
three hitherto unknown benzannulated pyranocoumarins
by following the inclusion in the sequence of a Diels–
Alder reaction as another atom-economic process. It is in-
teresting to note that the ring-closing enyne metathesis of
the internal olefins proceeded with E-stereoselectivity,
which is not often documented. The advantage of the
methodology lies in its true atom-economic nature, oper-
ational simplicity (only heat in most steps), catalytic use
of reagents, predetermined mode of cyclisation, and high
level of stereocontrol in the isomerisation as well as in the
RCEYM steps. Moreover, the sequence proceeds with
good overall yields. The methodology developed may
complement the existing methodologies26 for the prepara-
tion of pyrano- and benzopyrano-coumarin derivatives
and it may also find use in the preparation of related com-
pounds.
6-Allyloxy-2H-chromen-2-one (22)
The product was purified by column chromatography (EtOAc–PE,
25%).
Yield: 1.67 g (84%); colourless solid; mp 92–93 °C (EtOAc–PE)
(Lit.28 92 °C).
IR (KBr): 3419, 2983, 2912, 2864, 1726, 1573, 1489, 1429, 1341,
1259, 1180, 1098, 1010, 959 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.65 (d, J = 9.6 Hz, 1 H), 7.27 (d,
J = 8.8 Hz, 1 H), 7.13 (dd, J = 2.8, 8.8 Hz, 1 H). 6.94 (d, J = 2.8 Hz,
1 H), 6.43 (d, J = 9.6 Hz, 1 H), 6.11–6.01 (m, 1 H), 5.44 (dd, J = 1.2,
17.2 Hz, 1 H), 5.33 (dd, J = 1.2, 10.8 Hz, 1 H), 4.58 (dd, J = 0.8,
4.8 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 160.9, 154.9, 148.4, 143.3, 132.7,
120.0, 119.1, 118.0, 117.6, 116.9, 111.2, 69.3.
Melting points were recorded in open capillaries and are uncorrect-
ed. Infrared spectra were recorded with a Perkin–Elmer Spectrum 1
spectrophotometer. 1H and 13C NMR spectra were recorded with a
Bruker Avance 400 spectrometer purchased through a DST-FIST
grant. Chemical shifts are recorded relative to residual solvent peak.
Mass spectra were recorded with a JEOL-JMS 600 instrument from
I. I. C. B., Kolkata or IACS, Kolkata. Petroleum ether (PE) refers to
the fraction boiling in the range 60–80 °C. Silica gel (120–200
mesh) for column chromatography was purchased from Spectro-
chem, India.
Claisen Rearrangement of Allyloxycoumarins; General Proce-
dure
A solution of allyl ether 4, 15, or 22 (5 mmol) in diphenyl ether
(12.5 mL) was heated at reflux for 2 h under a nitrogen atmosphere.
The mixture was allowed to cool to r.t., then diluted with PE (50
mL). The precipitated solid was filtered off and then purified by
chromatography over silica gel (PE–EtOAc) to give the product 5,
16 or 23.
8-Allyl-7-hydroxy-4-methyl-2H-chromen-2-one (5)
The product was purified by column chromatography (EtOAc–PE,
25%).
Allylation of Hydroxycoumarins; General Procedure
A mixture of the appropriate hydroxycoumarin (10.0 mmol), allyl
bromide (15.0 mmol, 1.3 mL) and anhydrous K2CO3 (30.0 mmol,
4.2 g) in anhydrous acetone (25 mL) was heated to reflux for 12 h.
The mixture was then cooled, filtered and the filtrate was concen-
trated under reduced pressure. The residue was diluted with H2O
(20 mL) and then extracted with EtOAc (2 × 20 mL). The combined
extract was washed successively with sat. aq NaHCO3 (2 × 20 mL),
H2O (2 × 20 mL) and brine (30 mL), then dried (Na2SO4), filtered
and the filtrate was concentrated under reduced pressure to leave a
crude product, which was purified by column chromatography over
silica gel using EtOAc–PE as eluent.
Yield: 864 mg (80%); colourless solid; mp 206–207 °C (EtOAc–
PE) (Lit.16 198–199 °C).
IR (KBr): 3214, 1888, 1687, 1569, 1387, 1366, 1318, 1054,
995 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.41 (d, J = 8.4 Hz, 1 H), 6.86 (d,
J = 8.8 Hz, 1 H), 6.15 (s, 1 H), 6.05–5.97 (m, 1 H), 5.21–5.13 (m,
2 H), 3.68 (d, J = 6.0 Hz, 2 H), 2.41 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 160.8, 159.2, 154.2, 153.0, 135.9,
124.3, 115.4, 113.1, 112.5, 112.4, 110.4, 27.0, 18.6.
7-Allyloxy-4-methyl-2H-chromen-2-one (4)
The product was purified by column chromatography (EtOAc–PE,
10%).
6-Allyl-7-hydroxy-4,8-dimethyl-2H-chromen-2-one (16)
The product was purified by column chromatography (EtOAc–PE,
15%).
Yield: 1.77 g (82%); colourless solid; mp 104–106 °C (EtOAc–PE)
(Lit.16 103–104 °C).
Yield: 955 mg (83%); colourless solid; mp 172–174 °C (EtOAc–
PE) (Lit.27 168–170 °C).
IR (KBr): 3362, 2855, 1707, 1611, 1400, 1191, 1114, 902 cm–1.
IR (KBr): 2953, 2400, 1885, 1725, 1610, 1391, 1284, 1262, 1155,
1069, 994 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.50 (d, J = 8.8 Hz, 1 H), 6.88 (dd,
J = 2.4, 8.8 Hz, 1 H), 6.82 (d, J = 2.4 Hz, 1 H), 6.13 (s, 1 H), 6.08–
6.01 (m, 1 H), 5.45 (d, J = 17.2 Hz, 1 H), 5.34 (d, J = 10.8 Hz, 1 H),
4.60 (dd, J = 1.2, 5.2 Hz, 2 H), 2.40 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 161.5, 161.2, 155.1, 152.6, 132.2,
125.6, 118.4, 113.6, 112.7, 111.9, 101.7, 69.2, 18.6.
1H NMR (400 MHz, CDCl3): δ = 7.21 (s, 1 H), 6.14 (s, 1 H), 6.08–
6.00 (m, 1 H), 5.64 (s, 1 H,), 5.25–5.20 (m, 2 H,), 3.49 (d, J =
6.0 Hz, 2 H), 2.40 (s, 3 H), 2.34 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 161.9, 155.8, 153.1, 151.9, 135.8,
122.8, 121.8, 117.4, 113.4, 112.1, 111.7, 35.4, 18.8, 8.3.
5-Allyl-6-hydroxy-2H-chromen-2-one (23)
The product was purified by column chromatography (EtOAc–PE,
30%).
7-Allyloxy-4,8-dimethyl-2H-chromen-2-one (15)
The product was purified by column chromatography (EtOAc–PE,
15%).
Yield: 798 mg (79%); colourless solid; mp 164–165 °C (EtOAc–
PE) (Lit.28 159 °C).
Yield: 1.80 g (78%); colourless needles; mp 105–106 °C (EtOAc–
PE) (Lit.27 108 °C).
IR (KBr): 3404, 2755, 1878, 1709, 1605, 1373, 1286, 1129 cm–1.
IR (KBr): 3159, 1902, 1858, 1682, 1612, 1567, 1471, 1403, 1273,
1190, 825 cm–1.
© Georg Thieme Verlag Stuttgart · New York
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3336
S. K. Chattopadhyay et al.
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1H NMR (400 MHz, DMSO-d6): δ = 9.69 (s, 1 H), 8.08 (d, J =
10 Hz, 1 H), 7.13–7.08 (m, 2 H), 6.32 (d, J = 10.0 Hz, 1 H), 5.93–
5.85 (m, 1 H), 5.00–4.89 (m, 2 H), 3.57 (d, J = 5.6 Hz, 2 H).
13C NMR (100 MHz, DMSO-d6): δ = 160.4, 151.8, 147.8, 141.9,
136.9, 122.4, 119.8, 118.4, 116.2, 115.8, 115.4, 29.0.
Preparation of the Dienes 7, 18, 25, 8, 19 and 26
The title dienes were prepared by following the general procedure
described for the preparation of 4, 15 and 22 by using allyl bromide
as alkylating agent to obtain 7, 18 and 25, but using methallyl chlo-
ride in place of allyl bromide in case of compounds 8, 19 and 26.
7-Allyloxy-4-methyl-8-(prop-1-enyl)-2H-chromen-2-one (7)
The product was purified by column chromatography (EtOAc–PE,
15%).
Isomerisation of the 2-Allyl Hydroxycoumarins; General Pro-
cedure
To a stirred solution of the appropriate rearranged phenol 5, 16 or
23 (2.5 mmol) in benzene (20 mL), was added Ru(CO)ClH(PPh3)3
(40 mg, 2 mol%) under a nitrogen atmosphere and the mixture was
heated to reflux for 24 h. The solvent was removed under vacuum
and the resulting crude residue was subjected to column chromatog-
raphy on silica gel (EtOAc–PE). The product 6, 17 or 24 was ob-
tained as a colourless solid.
Yield: 768 mg (75%); colourless solid; mp 80–85 °C (EtOAc–PE).
IR (KBr): 3402, 2917, 1854, 1716, 1591, 1384, 1272, 1107,
1068 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.59 (d, J = 8.8 Hz, 1 H), 7.08 (d,
J = 9.2 Hz, 1 H), 6.75–6.69 (m, 1 H), 6.62 (d, J = 16.4 Hz, 1 H),
6.23 (s, 1 H,), 6.13–6.06 (m, 1 H,), 5.42 (dd, J = 1.6, 17.6 Hz, 1 H),
5.31 (d, J = 10.8 Hz, 1 H), 4.74–4.73 (m, 2 H), 2.39 (s, 3 H), 1.93
(d, J = 6.4 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 161.2, 158.7, 152.8, 151.8, 133.4,
132.6, 122.8, 119.4, 118.0, 114.8, 114.0, 112.0, 108.5, 69.6, 20.2,
18.9.
7-Hydroxy-4-methyl-8-(prop-1-enyl)-2H-chromen-2-one (6)
The product was purified by column chromatography (EtOAc–PE,
25%).
Yield: 448 mg (83%); colourless solid; mp 208–210 °C (EtOAc–
PE).
HRMS (TOF, ES+): m/z [M + H]+ calcd for C16H16O3: 257.1178;
found: 257.1184.
IR (KBr): 3256, 2913, 1698, 1595, 1563, 1438, 1367, 1356, 1388,
1312, 1286, 1058, 977 cm–1.
1H NMR (400 MHz, DMSO-d6): δ = 10.72 (s, 1 H), 7.46 (d, J =
8.4 Hz, 1 H), 6.89 (d, J = 8.8 Hz, 1 H), 6.80–6.71 (m, 1 H), 6.62 (d,
J = 16.0 Hz, 1 H), 6.16 (s, 1 H), 2.37 (s, 3 H), 1.92 (d, J = 6.4 Hz,
3 H).
13C NMR (100 MHz, DMSO-d6): δ = 160.6, 159.0, 154.3, 152.2,
131.6, 124.3, 120.4, 112.9, 112.5, 111.7, 110.5, 20.3, 18.8.
4-Methyl-7-(2-methylallyloxy)-8-(prop-1-enyl)-2H-chromen-2-
one (8)
The product was purified by column chromatography (EtOAc–PE,
20%).
Yield: 416 mg (77%); colourless solid; mp 78–80 °C (EtOAc–PE).
IR (KBr): 3404, 3062, 2850, 2911, 2762, 1888, 1728, 1699, 1595,
1558, 1448, 1431, 1370, 1386, 1284, 1083, 1118, 966 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.38 (d, J = 8.8 Hz, 1 H), 6.87–
6.75 (m, 3 H), 6.16 (s, 1 H), 5.08 (d, J = 8.4 Hz, 2 H), 4.57 (s, 2 H),
2.40 (d, J = 0.8 Hz, 3 H), 1.98 (d, J = 6.0 Hz, 3 H), 1.87 (s, 3 H).
HRMS (TOF, ES+): m/z [M + H]+ calcd for C13H12O3: 217.0865;
found: 217.0867.
7-Hydroxy-4,8-dimethyl-6-(prop-1-enyl)-2H-chromen-2-one
(17)
The product was purified by column chromatography (EtOAc–PE,
15%).
13C NMR (100 MHz, CDCl3): δ = 161.2, 158.7, 152.8, 151.7, 140.1,
133.3, 122.8, 119.4, 114.7, 113.9, 113.2, 111.9, 108.5, 72.5, 20.2,
19.5, 18.9.
HRMS (TOF, ES+): m/z [M + H]+ calcd for C17H18O3: 271.1334;
found: 271.1339.
Yield: 489 mg (85%); colourless solid; mp 142–144 °C (EtOAc–
PE).
IR (KBr): 3368, 2957, 1723, 1610, 1398, 1192, 1112 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.33 (s, 1 H), 6.57 (d, J = 16.0 Hz,
1 H), 6.24–6.17 (m, 1 H), 6.14 (s, 1 H), 5.65 (s, 1 H), 2.41 (s, 3 H),
2.34 (s, 3 H), 1.96 (dd, J = 1.6, 6.4 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 161.6, 154.1, 153.0, 151.8, 130.3,
124.8, 121.9, 120.3, 113.5, 111.8, 111.5, 18.9, 18.8, 8.4.
7-Allyloxy-4,8-dimethyl-6-(prop-1-enyl)-2H-chromen-2-one
(18)
The product was purified by column chromatography (EtOAc–PE,
10%).
Yield: 400 mg (74%); colourless solid; mp 114–116 °C (EtOAc–
PE).
HRMS (TOF, ES+): m/z [M + Na]+ calcd for C14H14O3: 253.0841;
found: 253.0864.
IR (KBr): 3403, 3057, 2977, 2852, 2341, 1716, 1652, 1603,
1422 cm–1.
6-Hydroxy-5-(prop-1-enyl)-2H-chromen-2-one (24)
The product was purified by column chromatography (EtOAc–PE,
30%).
1H NMR (400 MHz, CDCl3): δ = 7.48 (s, 1 H), 6.64 (dd, J = 1.2,
15.6 Hz, 1 H), 6.31–6.23 (m, 1 H), 6.21 (s, 1 H), 6.13–6.05 (m,
1 H), 5.43 (dd, J = 1.2, 16.8 Hz, 1 H), 5.30 (d, J = 10.4 Hz, 1 H),
4.35 (d, J = 5.6 Hz, 2 H), 2.43 (s, 3 H), 2.36 (s, 3 H), 1.94 (dd, J =
1.2, 6.4 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 161.2, 157.2, 152.6, 151.7, 133.2,
128.2, 127.8, 125.2, 119.8, 119.1, 118.0, 116.4, 113.5, 74.5, 18.9
(two signals), 9.3.
Yield: 384 mg (76%); colourless solid; mp 126–130 °C (EtOAc–
PE).
IR (KBr): 3181, 1893, 1678, 1599, 1567, 1468, 1400, 1293, 1267,
1191, 947, 826 cm–1.
1H NMR (400 MHz, DMSO-d6): δ = 9.81 (s, 1 H), 8.23 (d, J =
9.6 Hz, 1 H), 7.14–7.08 (m, 2 H), 6.59 (dd, J = 1.2, 15.6 Hz, 1 H),
6.41 (d, J = 10.0 Hz, 1 H), 6.16 (qd, J = 6.8, 16.0 Hz, 1 H), 1.93 (d,
J = 6.4 Hz, 3 H).
HRMS (TOF, ES+): m/z [M + Na]+ calcd for C17H18O3: 293.1154;
found: 293.1161.
13C NMR (100 MHz, DMSO-d6): δ = 160.4, 151.7, 148.0, 142.4,
133.9, 123.2, 122.1, 119.8, 117.2, 115.9, 115.5, 19.7.
HRMS (TOF, ES+): m/z [M + H]+ calcd for C12H10O3: 203.0708;
found: 203.0710.
4,8-Dimethyl-7-(2-methylallyloxy)-6-(prop-1-enyl)-2H-
chromen-2-one (19)
The product was purified by column chromatography (EtOAc–PE,
15%).
Yield: 466 mg (82%); colourless solid; mp 98–99 °C (EtOAc–PE).
IR (KBr): 3413, 3020, 2919, 1714, 1216, 1108, 761 cm–1.
Synthesis 2014, 46, 3331–3340
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Synthesis of Pyranocoumarins and Benzopyranocoumarins
3337
1H NMR (400 MHz, CDCl3): δ = 7.48 (s, 1 H), 6.66 (d, J = 16.0 Hz,
1 H), 6.31–6.23 (m, 1 H), 6.21 (s, 1 H), 5.18 (s, 1 H), 5.04 (s, 1 H),
4.20 (s, 2 H), 2.44 (s, 3 H), 2.37 (s, 3 H), 1.94 (d, J = 1.6 Hz, 3 H),
1.92 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 161.2, 157.3, 152.6, 151.7, 140.9,
128.2, 127.7, 125.1, 119.8, 119.1, 116.4, 113.5, 113.1, 77.1, 19.7,
18.9 (two signals), 9.1.
1H NMR (400 MHz, CDCl3): δ = 7.35 (d, J = 8.8 Hz, 1 H), 6.99 (d,
J = 10.0 Hz, 1 H), 6.74 (d, J = 8.4 Hz, 1 H), 6.14 (s, 1 H), 5.89–5.85
(m, 1 H), 4.94 (dd, J = 2.0, 3.2 Hz, 2 H), 2.39 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 160.9, 156.9, 152.9, 149.3, 124.6,
121.8, 117.6, 114.0, 112.5, 111.8, 110.2, 66.0, 18.8.
HRMS (TOF, ES+): m/z [M + Na]+ calcd for C13H10O3: 237.0528;
found: 237.0529.
HRMS (TOF, ES+): m/z [M + H]+ calcd for C18H20O3: 285.1491;
found: 285.1495.
4,9-Dimethyl-8H-pyrano[2,3-h]chromen-2-one (12)
The product was purified by column chromatography (EtOAc–PE,
15%).
6-Allyloxy-5-(prop-1-enyl)-2H-chromen-2-one (25)
The product was purified by column chromatography (EtOAc–PE,
25%).
Yield: 172 mg (84%); colourless solid; mp 128–130 °C (EtOAc–
PE).
Yield: 387 mg (80%); colourless solid; mp 70–75 °C (EtOAc–PE).
IR (KBr): 3402, 3058, 2852, 2920, 1844, 1728, 1596, 1496, 1450,
1366, 1380, 1261, 1162, 1074, 999 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.29 (d, J = 8.4 Hz, 1 H), 6.74 (d,
J = 3.2 Hz, 1 H), 6.71 (s, 1 H), 6.12 (s, 1 H), 4.78 (s, 2 H), 2.37 (s,
3 H), 1.85 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 161.2, 155.5, 153.0, 148.7, 131.5,
123.4, 114.0, 112.3, 112.1, 111.7, 110.7, 69.5, 19.2, 18.8.
HRMS (TOF, ES+): m/z [M + Na]+ calcd for C14H12O3: 251.0684;
IR (KBr): 3085, 2970, 1863, 1725, 1592, 1565, 1450, 1442, 1278,
1267, 1109, 917 cm–1.
1H NMR (400 MHz, CDCl3): δ = 8.09 (d, J = 9.6 Hz, 1 H), 7.15 (d,
J = 8.8 Hz, 1 H), 7.06 (d, J = 9.2 Hz, 1 H), 6.56 (dd, J = 1.2,
16.0 Hz, 1 H), 6.38 (d, J = 10.0 Hz, 1 H), 6.10–5.95 (m, 2 H), 5.41
(dd, J = 1.2, 17.2 Hz, 1 H), 5.30 (dd, J = 0.8, 10.4 Hz, 1 H), 4.59–
4.57 (m, 2 H), 2.00 (dd, J = 1.6, 6.8 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 160.9, 152.1, 149.0, 141.8, 134.7,
133.0, 126.0, 122.6, 117.7, 117.5, 116.3, 116.1, 115.2, 70.0, 19.3.
found: 251.0685.
HRMS (TOF, ES+): m/z [M + H]+ calcd for C15H14O3: 243.1021;
found: 243.1027.
4,10-Dimethylpyrano[3,2-g]chromen-2-(8H)-one (20)
The product was purified by column chromatography (EtOAc–PE,
10%).
6-(2-Methylallyloxy)-5-(prop-1-enyl)-2H-chromen-2-one (26)
The product was purified by column chromatography (EtOAc–PE,
20%).
Yield: 178 mg (87%); colourless solid; mp 178–180 °C (EtOAc–
PE) (Lit.29 176–179 °C).
IR (KBr): 3393, 2925, 2864, 2328, 1704, 1654, 1616, 1574 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.01 (s, 1 H), 6.45 (dt, J = 1.6,
10.0 Hz, 1 H), 6.11 (d, J = 1.0 Hz, 1 H), 5.82 (dt, J = 3.6, 10.0 Hz,
1 H), 4.95 (dd, J = 2.0, 3.2 Hz, 2 H), 2.37 (s, 3 H), 2.24 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 161.4, 155.1, 152.9, 152.7, 123.6,
121.8, 119.2, 118.2, 113.6, 113.1, 111.7, 66.2, 18.8, 7.9.
Yield: 400 mg (78%); colourless gummy liquid.
IR (CHCl3): 3083, 2916, 1730, 1567, 1448, 1266, 1085 cm–1.
1H NMR (400 MHz, CDCl3): δ = 8.09 (d, J = 9.6 Hz, 1 H), [7.76 (d,
J = 9.6 Hz, 0.3 H)], 7.15 (d, J = 0.8 Hz, 1 H), [7.20 (d, J = 8.8 Hz,
0.3 H)], 7.09–7.04 (m, 1.3 H), 6.57 (d, J = 16.0 Hz, 1 H), 6.44–6.37
(m, 1.6 H), 6.03–5.96 (m, 1.3 H), 5.05–5.00 (two singlets, 2.6 H),
4.47 (s, 2.6 H), 2.00 (d, J = 6.0 Hz, 3 H), [1.53 (d, J = 6.4 Hz,
0.99 H)], 1.82 (d, J = 7.6 Hz, 3 H).
HRMS (TOF, ES+): m/z [M + H]+ calcd for C14H12O3: 229.0865;
found: 229.0870.
13C NMR (100 MHz, CDCl3): δ = 160.8, 152.2, 152.1, 148.9, 148.4,
142.0, 141.7, 140.5, 134.5, 131.0, 125.7, 124.3, 122.5, 122.0, 117.7,
117.3, 116.3, 116.1, 116.0, 115.6, 115.1, 112.7, 112.6, 72.7, 72.6,
19.4, 19.3, 15.0.
HRMS (TOF, ES+): m/z [M + H]+ calcd for C16H16O3: 257.1178;
found: 257.1187.
4,7,10-Trimethylpyrano[3,2-g]chromen-2-(8H)-one (21)
The product was purified by column chromatography (EtOAc–PE,
20%).
Yield: 181 mg (83%); colourless solid; mp 106–107 °C (EtOAc–
PE).
IR (KBr): 3394, 3279, 2921, 2346, 1714, 1610, 1575, 1405, 1381,
1190, 1113 cm–1.
1H NMR (400 MHz, CDCl3): δ = 6.94 (s, 1 H), 6.18 (s, 1 H), 6.10
(s, 1 H), 4.80 (s, 2 H), 2.36 (s, 3 H), 2.24 (s, 3 H), 1.82 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 161.6, 153.8, 152.8, 152.4, 131.0,
118.8, 118.5, 118.0, 113.5, 112.6, 111.6, 69.6, 18.8 (two signals),
8.0.
Preparation of Pyranocoumarins 10, 12, 20, 21, 27 and 28 by
RCM Reaction; General Procedure
Grubbs’ catalyst 9 (5 mol%) was added to a stirred solution of the
appropriate diene 7, 18 or 25 (0.9 mmol) in anhydrous, degassed
benzene (35 mL) under argon and the mixture was heated to reflux
for 24 h until the disappearance of starting material was observed.
The reaction mixture was then concentrated under reduced pressure
and the residual mass was purified by chromatography over silica
gel (EtOAc–PE) to afford the desired cyclic compound 10, 20 or 27.
Compounds 12, 21 and 28 were prepared similarly by following the
above procedure but using the Grubbs second-generation catalyst
11.
HRMS (TOF, ES+): m/z [M + H]+ calcd for C15H14O3: 243.1021;
found: 243.1026.
Pyrano[3,2-f]chromen-3(8H)-one (27)
The product was purified by column chromatography (EtOAc–PE,
30%).
4-Methyl-8H-pyrano[2,3-h]chromen-2-one (10)
The product was purified by column chromatography (EtOAc–PE,
15%).
Yield: 147 mg (82%); colourless solid; mp 138–140 °C (EtOAc–
PE) (Lit.30 140 °C).
IR (KBr): 3386, 3079, 2924, 2854, 1719, 1588, 1569, 1462, 1254,
1184 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.88 (d, J = 9.6 Hz, 1 H), 7.10 (d,
J = 8.8 Hz, 1 H), 6.99 (d, J = 9.2 Hz, 1 H), 6.80 (d, J = 9.6 Hz, 1 H),
Yield: 163 mg (85%); colourless solid; mp 180–182 °C (EtOAc–
PE) (Lit.29 184 °C).
IR (KBr): 3403, 3055, 2924, 2854, 1714, 1598, 1398, 1380, 1240,
1268, 1099, 997 cm–1.
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2014, 46, 3331–3340

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S. K. Chattopadhyay et al.
PAPER
5-(Prop-1-enyl)-6-(prop-2-ynyloxy)-2H-chromen-2-one (33)
6.44 (d, J = 10.0 Hz, 1 H), 6.05–6.01 (m, 1 H), 4.83 (dd, J = 2.0,
The product was purified by column chromatography (EtOAc–PE,
25%).
3.6 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 160.7, 150.3, 149.0, 138.5, 124.8,
120.0, 119.1, 118.3, 116.8, 116.7, 114.4, 65.2.
Yield: 374 mg (78%); colourless solid; mp 88–90 °C (EtOAc–PE).
HRMS (TOF, ES+): m/z [M + Na]+ calcd for C12H8O3: 223.0371;
found: 223.0371.
IR (KBr): 3434, 3246, 2119, 1737, 1565, 1450, 1269, 1119, 1071,
802 cm–1.
1H NMR (400 MHz, CDCl3): δ = 8.08 (d, J = 9.6 Hz, 1 H), 7.26–
7.18 (m, 2 H), 6.55 (d, J = 16.0 Hz, 1 H), 6.43–6.38 (m, 1 H), 6.03–
5.96 (m, 1 H), 4.74 (d, J = 2.0 Hz, 2 H), 2.53–2.51 (m, 1 H), 2.00
(dd, J = 1.6, 6.4 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 160.8, 151.0, 149.6, 141.7, 135.1,
122.3, 117.6, 117.1, 116.6, 116.2, 115.2, 78.3, 76.1, 57.1, 19.3.
9-Methylpyrano[3,2-f]chromen-3(8H)-one (28)
The product was purified by column chromatography (EtOAc–PE,
20%).
Yield: 156 mg (81%); light-yellow solid; mp 84–85 °C (EtOAc–
PE).
IR (KBr): 3371, 3086, 2965, 2921, 2851, 1713, 1593, 1567, 1464,
1348, 1248, 1120, 826 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.91 (d, J = 10.0 Hz, 1 H), 7.05 (d,
J = 8.8 Hz, 1 H), 6.97 (d, J = 8.8 Hz, 1 H), 6.53 (s, 1 H), 6.42 (d, J =
10.0 Hz, 1 H), 4.70 (d, J = 0.4 Hz, 2 H), 1.92 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 160.8, 149.1, 148.7, 138.6, 135.0,
119.5, 119.0, 116.3, 115.6, 113.9, 113.8, 68.9, 19.6.
HRMS (TOF, ES+): m/z [M+] calcd for C13H10O3: 214.0630; found:
HRMS (TOF, ES+): m/z [M + Na]+ calcd for C15H12O3: 263.0684;
found: 263.0698.
RCEYM Reaction of 29, 31 and 33; General Procedure
Grubbs’ catalyst 11 (5 mol%) was added to a stirred solution of the
appropriate enyne derivative 29, 31 or 33 (1 mmol), in anhydrous
degassed benzene (30 mL) under an argon atmosphere, and the re-
action mixture was heated at reflux for 24 h. After removal of the
solvent in vacuo, the crude product was purified by column chroma-
tography over silica gel (EtOAc–PE) to afford diene 30, 32 or 34.
214.0651.
Preparation of Propargyl Ethers 29, 31 and 33
Prepared by following the general procedure described for the
preparation of 4, 15 and 22, but using propargyl bromide in place of
allyl bromide.
(E,Z)-4-Methyl-9-(prop-1-enyl)-pyrano[2,3-h]chromen-2(8H)-
one (30)
The product was purified by column chromatography (EtOAc–PE,
20%). The product was obtained as a mixture of two geometric iso-
mers in which the E-isomer was enriched. NMR data for the major
isomer is given below.
4-Methyl-8-(prop-1-enyl)-7-(prop-2-ynyloxy)-2H-chromen-2-
one (29)
The product was purified by column chromatography (EtOAc–PE,
20%).
Yield: 178 mg (70%); colourless solid; mp 132–134 °C (EtOAc–
PE).
IR (KBr): 3423, 2925, 2853, 1717, 1598, 1373, 1174, 1083 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.32–7.26 (m, 1 H), 6.86–6.72 (m,
2 H), 6.20 (d, J = 16.0 Hz, 1 H), 6.12 (s, 1 H), 5.78–5.63 (m, 1 H),
5.01 (d, J = 5.2 Hz, 2 H), 2.37 (s, 3 H), 1.86 (d, J = 6.4 Hz, 3 H).
Yield: 404 mg (79%); colourless solid; mp 140–142 °C (EtOAc–
PE).
IR (KBr): 3381, 3231, 2931, 2122, 1867, 1695, 1591, 1382, 1368,
1273, 1250, 1117, 1075, 984 cm–1.
13C NMR (100 MHz, CDCl3): δ = 161.1, 156.1, 153.0, 149.3, 130.7,
129.3, 127.0, 123.7, 114.0, 113.5, 112.1, 111.8, 110.9, 66.2, 18.8
(two signals).
1H NMR (400 MHz, CDCl3): δ = 7.41 (d, J = 8.8 Hz, 1 H), 6.99 (d,
J = 8.8 Hz, 1 H), 6.85–6.78 (m, 1 H), 6.72 (d, J = 16.0 Hz, 1 H),
6.16 (s, 1 H), 4.83 (d, J = 2.0 Hz, 2 H), 2.57 (t, J = 2.0 Hz, 1 H), 2.40
(s, 3 H), 1.98 (d, J = 6.4 Hz, 3 H).
HRMS (TOF, ES+): m/z [M + H]+ calcd for C16H14O3: 255.1021;
13C NMR (100 MHz, CDCl3): δ = 161.0, 157.5, 152.7, 151.7, 133.8,
122.7, 119.1, 115.2, 114.6, 112.4, 108.7, 77.9, 76.3, 56.5, 20.2,
18.9.
HRMS (TOF, ES+): m/z [M + H]+ calcd for C16H14O3: 255.1021;
found: 255.1027.
found: 255.1026.
(E)-4,10-Dimethyl-6-(prop-1-enyl)-pyrano[3,2-g]chromen-
2(8H)-one (32)
The product was purified by column chromatography (EtOAc–PE,
6%).
Yield: 192 mg (72%); colourless solid; mp 128–129 °C (EtOAc–
PE).
IR (KBr): 2964, 2350, 1714, 1614, 1574, 1408, 1388 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.36 (s, 1 H), 7.02 (s, 1 H), 6.28
(s, 1 H), 6.11 (s, 1 H), 5.65 (m, 1 H), 5.04 (s, 2 H), 2.37 (s, 3 H),
2.26 (s, 3 H), 1.86 (d, J = 6.0 Hz, 3 H).
4,8-Dimethyl-6-(prop-1-enyl)-7-(prop-2-ynyloxy)-2H-chromen-
2-one (31)
The product was purified by column chromatography (EtOAc–PE,
10%).
Yield: 348 mg (65%); colourless solid; mp 125–127 °C (EtOAc–
PE).
13C NMR (100 MHz, CDCl3): δ = 161.4, 154.4, 152.7, 152.6, 130.6,
128.9, 126.4, 121.7, 119.8, 118.8, 113.8, 112.7, 111.7, 66.2, 18.8
(two signals), 8.0.
HRMS (TOF, ES+): m/z [M + Na]+ calcd for C17H16O3: 291.0997;
found: 291.0986.
IR (KBr): 3738, 3236, 2966, 2325, 2122, 1706, 1621, 1571,
1603 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.47 (s, 1 H), 6.67 (d, J = 15.6 Hz,
1 H), 6.30–6.23 (m, 2 H), 4.57 (d, J = 2.4 Hz, 2 H), 2.52 (t, J =
2.4 Hz, 1 H), 2.43 (s, 3 H), 2.41 (s, 3 H), 1.95 (dd, J = 1.6, 6.4 Hz,
3 H).
(E)-9-(Prop-1-enyl)pyrano[3,2-f]chromen-3(8H)-one (34)
The product was purified by column chromatography (EtOAc–PE,
20%).
13C NMR (100 MHz, CDCl3): δ = 161.1, 156.2, 152.5, 151.6, 128.3,
128.2, 125.1, 120.4, 119.4, 116.8, 113.8, 78.4, 75.8, 60.9, 18.9 (two
signals), 9.6.
Yield: 180 mg (75%); colourless solid; mp 126–127 °C (EtOAc–
PE).
HRMS (TOF, ES+): m/z [M + Na]+ calcd for C17H16O3: 291.0997;
found: 291.0986.
IR (KBr): 3402, 3075, 2923, 2851, 1727, 1564, 1464, 1443, 1251,
1023 cm–1.
Synthesis 2014, 46, 3331–3340
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Synthesis of Pyranocoumarins and Benzopyranocoumarins
3339
1H NMR (400 MHz, CDCl3): δ = 7.92 (d, J = 9.6 Hz, 1 H), 7.06 (d,
J = 8.8 Hz, 1 H), 7.00 (d, J = 9.2 Hz, 1 H), 6.60 (s, 1 H), 6.44 (d, J =
10.0 Hz, 1 H), 6.24 (d, J = 16.0 Hz, 1 H), 5.84–5.77 (m, 1 H), 4.95
(s, 2 H), 1.90 (d, J = 6.8 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 160.8, 149.6, 149.2, 138.5, 133.8,
129.2, 128.4, 119.5, 119.2, 116.3, 115.9, 114.8, 114.2, 65.4, 18.8.
HRMS (TOF, ES+): m/z [M + Na]+ calcd for C23H20O7: 431.1107;
found: 431.1107.
Acknowledgment
Financial assistance from DST, New Delhi (Grant No. SR/S1/OC-
92/2012), and CSIR, Govt. of India (02/0164/12/EMR-II) are grate-
fully acknowledged. We are also thankful to the University of Ka-
lyani for a fellowship to P.M. Assistance from the DST- PURSE
program is also thankfully acknowledged.
HRMS (TOF, ES+): m/z [M + Na]+ calcd for C15H12O3: 263.0684;
found: 263.0683.
Diels–Alder Reaction of Dienes 30, 32 and 34; General Proce-
dure
To a stirred solution of the appropriate diene 30, 32 or 34 (0.3
mmol) in anhydrous toluene (5 mL), dimethyl acetylenedicarboxyl-
ate or diethyl acetylenedicarboxylate (0.75 mmol, 2.5 equiv) was
added and the mixture was heated to reflux for 48 h. The solvent
was evaporated under reduced pressure and the residual mass was
purified by column chromatography over silica gel (EtOAc–PE) to
give the corresponding aromatised cycloadduct 39, 41 or 43.
Supporting Information for this article is available online
at
http://www.thieme-connect.com/products/ejournals/journal/
10.1055/s-00000084.SunogIpimrfiantoSuIpg
n
fonirtat
ori
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Compound 39
The product was purified by column chromatography (EtOAc–PE,
30%).
Yield: 90 mg (71%); colourless solid; mp 150–152 °C (EtOAc–PE).
IR (KBr): 3431, 2923, 2986, 1736, 1594, 1376, 1316, 1206,
1078 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.52 (d, J = 8.4 Hz, 1 H), 7.21 (s,
1 H), 7.05 (d, J = 8.8 Hz, 1 H), 6.15 (s, 1 H), 4.95 (s, 2 H), 4.38 (q,
J = 7.2 Hz, 2 H), 4.15 (q, J = 7.0 Hz, 2 H), 2.42 (d, J = 4.0 Hz, 6 H),
1.38 (t, J =7.2 Hz, 3 H), 1.29 (t, J = 7.2 Hz, 3 H).
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13C NMR (100 MHz, CDCl3): δ = 168.3, 167.5, 165.9, 159.9, 159.7,
152.8, 151.2, 136.6, 135.5, 134.8, 129.5, 128.5, 125.4, 114.9, 114.0,
112.3, 111.9, 69.8, 61.9, 61.5, 19.7, 19.1, 14.1, 13.5.
HRMS (TOF, ES+): m/z [M + Na]+ calcd for C24H22O7: 445.1263;
found: 445.1262
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Compound 41
The product was purified by column chromatography (EtOAc–PE,
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Yield: 75 mg (61%); colourless solid; mp 115–116 °C (EtOAc–PE).
IR (KBr): 3438, 3006, 2957, 1724, 1611, 1578 cm–1.
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1H NMR (400 MHz, CDCl3): δ = 7.54 (s, 1 H), 7.18 (s, 1 H), 6.19
(s, 1 H), 5.05 (s, 2 H), 3.92 (s, 3 H), 3.84 (s, 3 H), 2.45 (s, 3 H), 2.38
(s, 3 H), 2.37 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 170.0, 167.9, 160.9, 152.8, 152.3,
136.5, 136.3, 132.3, 129.2, 128.6, 128.3, 125.5, 119.1, 117.9, 115.3,
114.6, 113.0, 69.0, 52.8, 52.6, 20.1, 18.7, 8.4.
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HRMS (TOF, ES+): m/z [M + Na]+ calcd for C23H20O7: 431.1107;
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Compound 43
The product was purified by column chromatography (EtOAc–PE,
25%).
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Yield: 92 mg (75%); colourless solid; mp 120–122 °C (EtOAc–PE).
IR (KBr): 3431, 2927, 1731, 1570, 1466, 1231, 1103, 1029,
757 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.85 (d, J = 9.6 Hz, 1 H), 7.31–
7.26 (m, 3 H), 6.37 (d, J = 9.6 Hz, 1 H), 5.10 (d, J = 12.8 Hz, 1 H),
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Synthesis 2014, 46, 3331–3340

3340
S. K. Chattopadhyay et al.
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