Intramolecular carbonyl-ene reactions in the synthesis of peri-oxygenated hydroaromatics

Article abstract of DOI:10.1016/j.tet.2016.02.033

2-Methallyl aromatic aldehydes, synthesized by Suzuki coupling of 2-formylphenylboronic acids, are shown to provide cycloalkylidene ene products under acidic conditions. Susceptibility of the products to aromatization is manoeuvred by varying the reaction conditions and catalysts including binol-derived Br?nsted acid catalysts. A peri-effect is identified as a controlling factor for the aromatizations. Several oxidative transformations of an ene product are carried out as model studies of hydroaromatic polyketide natural products.

Full text of DOI:10.1016/j.tet.2016.02.033

Tetrahedron 72 (2016) 1758e1772
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Tetrahedron
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Intramolecular carbonyl-ene reactions in the synthesis of
peri-oxygenated hydroaromatics
*
Shyam Basak, Dipakranjan Mal
Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur 721302, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 January 2016
Received in revised form 12 February 2016
Accepted 15 February 2016
Available online 17 February 2016
2-Methallyl aromatic aldehydes, synthesized by Suzuki coupling of 2-formylphenylboronic acids, are
shown to provide cycloalkylidene ene products under acidic conditions. Susceptibility of the products to
aromatization is manoeuvred by varying the reaction conditions and catalysts including binol-derived
Brønsted acid catalysts. A peri-effect is identified as a controlling factor for the aromatizations. Several
oxidative transformations of an ene product are carried out as model studies of hydroaromatic poly-
ketide natural products.
Keywords:
Ó 2016 Elsevier Ltd. All rights reserved.
Intramolecular
Carbonyl-ene
Hydroaromatics
Anthracyclines
1. Introduction
The present report stems from the seminal work of Hauser and
Mal on carbonyl-ene reaction in the construction of hydroaromatic
The ene reaction is a fundamentally important carbonecarbon
single bond forming reaction.1 It has been a key step in many classic
syntheses including asymmetric syntheses.2 Studied in depth by
many researchers, it continues to attract attention of the organic
chemists due to its enormous applicability in organic synthesis.
Among the various subclasses of the ene reactions, type-II intra-
molecular carbonyl-ene reaction (ICE) (Scheme 1) is more elabo-
rately studied.1
ring A of anthracyclines. Treatment of a methallylanthraquinone
carboxaldehyde with SnCl4$5H2O in DCM resulted in the formation
of a tetracycle.5 It is presumably the first report of a type-II ICE
reaction in the formation of a hydroaromatic system. The applica-
tions of such reactions, however, are limited to few
methoxyanthraquinone-embedded precursors.6 In view of the
wide occurrence7 of hydroaromatics, especially the m-cresol unit in
natural products 1e9 (Fig. 1), we intended to validate the potential
of the reaction for
hydroaromatics.
a
general synthesis of oxygenated
H2C
H2C
H
n
n
Herein, we report regiocontrolled construction of oxygenated
hydroaromatics with naphthalene, anthracene and naphthacene
nuclei, as well as their ene precursors. Susceptibility of the ene
products to aromatization has been correlated with their struc-
tures.8 Oxidation chemistry of an ene product has been briefly
explored as models, for the terminal ring in the natural products.
OH
O
Scheme 1. Typical type-II carbonyl-ene reaction of an alicyclic compound.
Like the general ene reaction, type-II ICE reaction has facilitated
many total syntheses in atom-economic manner and made their
ways to the industries. Examples of the total syntheses are those of
natural products (þ)-cassiol, laulimalide, (þ)-azaspiracid-1 etc.3
The mechanistic aspects of the reaction have thoroughly been ex-
amined.4 However, its scope is largely confined to the alicyclic
compounds.1
2. Results and discussion
Synthesis of the aldehyde-ene precursors: The majority of the
ene-precursors of this study are not reported in the literature. In
general, the synthesis of methallylarenes is scarcely reported.9a The
Suzuki coupling9b,9c was adopted as the key step for the synthesis
of ene-precursors 10e16 (109b, 119d, 129e, 149feh) and boronic acids
17e26 (1810a,10b, 2210c) were employed for this coupling reactions
(Scheme 2). Initial attempt of the coupling of 17 with methallyl
bromide in presence of PdCl2(PPh3)2 gave the desired product 10 in
* Corresponding author. Fax: þ91 3222282252; e-mail address: dmal@chem.
iitkgp.ernet.in (D. Mal).
http://dx.doi.org/10.1016/j.tet.2016.02.033
0040-4020/Ó 2016 Elsevier Ltd. All rights reserved.

S. Basak, D. Mal / Tetrahedron 72 (2016) 1758e1772
1759
OH
O
O
OH
OH
O
OH
H3CO
H3CO
OH
OH
OH
O
OH
O
Balticol C (1)
6-Methylxanthopurpurin-
Altersolanol P (3)
3-O-methyl ether (2)
O
O
O
OH
O
OH
HO
OH
O
HO
HO
HO
O
O
OH OH
OH
OH
OH
O
OH
O
O
O
HO
HO
OH
Galtamycinone (4)
Nocatriones A (5)
Aranciamycin l (6)
O
HO
O
O
O
OH
O
O
OH
OH
OH
OH
O
HO
HO
O
OH OH
OH
O
O
Idarubicinone (7)
Aquayamycin (8)
Tetrangomycin (9)
Fig. 1. Structures of selected natural products with oxygenated tetralin skeletons.
R5
Br
R1
R1
R1
OH
2.5 mol% PdCl2(PPh3)2
aq. Na2CO3, THF
inert atmosphere
R2
R3
B(OH)2
CHO
R2
R3
R2
R3
B
R5
or
O
CHO
R4
17 R1 = R2 = R3 = R4 = H
18 R1 = R2 = R4 = H, R3 = OMe 21 R1 = R4 = OMe, R2 = R3 = H
20 R1 = R4 = OMe, R2 = R3 = H 24 R1, R2= , R3 = R4 = H
22 R1 = R4 = H, R2 = R3 = OMe 26 R1 = R2 = H, R3, R4
23 R1, R2 , R3 = R4 = H
25 R1 = R2 = H, R3, R4
R4
R4
OH
10 R1 = R2 = R3 = R4 = R5 = H; 71%
19 R1 = R2 = R4 = H, R3 = OMe
11 R1 = R2 = R3 = R4 = H, R5 = Me; 73%
12 R1 = R2 = R4 = R5 = H, R3 = OMe; 60%
13 R1 = R4 = OMe, R2 = R3 = R5 = H; 80%
14 R1 = R4 = R5 = H, R2 = R3 = OMe; 71%
=
=
15 R1, R2=
16 R1 = R2= R5 = H, R3, R4
Scheme 2. Synthesis of ene-precursors by Suzuki reaction.
, R3 = R4 = R5 = H; 50%
=
=
;68%
40% yield. However, the yield could be significantly improved i.e.
up to 71% by adding the boronic acid 17 portion wise as well as
increasing the amount of the methallyl bromide. This modification
was applied for the synthesis of all other compounds (11e16). This
modification allowed minimum formation of the biphenyl
dicarboxaldehyde.
Ene precursor 27 was synthesized in four steps from isovanillin
derivative 2811. It was reduced to 29 with NaBH4, which was ther-
mally rearranged to give 30. O-methylation of compound 30 fol-
lowed by MnO2 oxidation of 31 furnished aldehyde 27 (Scheme 3).
Keeping in the mind the structural features of altersolanol P7b
(3) as well as truncated anthracyclines12a, naphthaldehyde 32
was chosen as the model substrate. It was prepared in seven steps
as shown in Scheme 4. Hauser annulation12ced of cyanophthalide
3312e with methyl acrylate was performed to give 1,4-naph-
thoquinol 34, which was selectively monomethallylated to give 35.
After O-methylation of 35, the resulting ether 36 was subjected to
Claisen rearrangement in refluxing DMF followed by methylation
to give naphthalene derivative 37. LAH reduction of 37 to alcohol 38
followed by PCC oxidation of 38 provided ene precursor 32
(Scheme 4).
Alkylidene malonate 39 was prepared by Knoevenagel reaction
of 10 with dimethyl malonate in the presence of piperidine and
OR
O
O
MnO2
DCM
i) DMF, reflux
53%
O
O
O
ii) MeI, K2CO3
acetone
99%
95%
R
CHO
OH
30 R = H
31 R = Me
28 R = CHO
29 R = CH2OH
NaBH4, 79%
27
Scheme 3. Synthesis of metthallylbenzaldehyde 27.

1760
S. Basak, D. Mal / Tetrahedron 72 (2016) 1758e1772
Br
i) LiOBu-t, THF
-78 °C,
OH
OH
O
CN
O
K2CO3, acetone,
0 °C_rt
NaH, Me2SO4,
THF
ii) H3O+
95%
55%
85%
COOCH3
CO2CH3
CO2CH3
O
O
O
O
OH
33
34
35
i) DMF, reflux,12 h
ii) Me2SO4, K2CO3,
acetone
O
O
O
O
O
LAH, THF, rt
30 h, 86%
70%
CO2CH3
CO2CH3
R
O
O
O
O
PCC
DCM, rt
88%
36
37
38 R = CH2OH
32 R = CHO
Scheme 4. Model studies on the synthesis of altersolanol-p.
acetic acid in benzene. Ene substrate 40 was prepared from 10 by
Wittig reaction with carbethoxymethylenetriphenylphosphorane.
Ene substrate 41 was prepared from 2-bromobenzaldehyde fol-
lowing literature procedure (Fig. 2).13
involving dry ethyl acetate (EA) containing 50 mol% SnCl4$5H2O
were most effective. The isolated yields of the ene products 42 and
43 were 82% and 9% respectively under these conditions (Table 3).
2.3. Scope of substrates
Following the optimization study, we examined substrates 11,
12, 15, 16 for the ICE as detailed in Table 3. Our primary goal was to
intercept hydroaromatic products of the reactions. From the in-
spection of the results in Table 3, it is apparent that such objectives
are achievable to great extent by changing the reaction conditions.
Application of the optimized conditions (SnCl4$5H2O in EA) to
ethyl analogue of 10 i.e. 11 also delivered nonaromatized desired
CHO
MeO2C
CO2Me
CO2Et
39
40
Fig. 2. Ene precursors 39e41.
41
2.1. Preliminary studies with SnCl4$5H2O
Table 1
ICE reaction of selected substrates with SnCl4$5H2O, DCM at rt (Hauser protocol)a
Preliminary studies were conducted with 109b under Hauser
conditions (SnCl4$5H2O in DCM). When it was treated with 50 mol%
SnCl4$5H2O5, the desired methylidene tetrahydronaphthol 42 was
obtained in 39% yield along with 2-methylnaphthalene (43)14 in
50% yield. The structure of 42 was established by its characteristic
Substrates
Non-aromatized ene
products (%yield)
Aromatized ene
products (%yield)
1H NMR signals at
d 4.99 (s, 1H) and 4.92 (s, 1H) due to exocyclic
olefinic protons. The generation of a double bond exocyclic to the
new ring in 42 suggests that the ene cyclization is a concerted one
as shown in the proposed T.S. (Fig. 3). For the corresponding
stepwise process, a product with an endocyclic double bond is
expected due to conjugative stability of the product. Ene precursors
12, 13, 16 were also employed for the ICE reaction under same re-
action conditions, and in all the cases aromatized products (44, 45,
46) were exclusively obtained (Table 1).
d
2.2. Model studies
In order to optimize the conditions, precursor 10 was chosen. To
minimize the formation of aromatized product 43, the reaction
conditions were optimized as shown in Table 2. Conditions
d
d
Half chair
conformation
H
O
H
Chair
conformation
LA or BA
a
All reactions were carried out for 1e2 h.
Fig. 3. Proposed T.S.

S. Basak, D. Mal / Tetrahedron 72 (2016) 1758e1772
1761
Table 2
other methoxy substituted ene-precursors. Under the optimized
conditions i.e. SnCl4$5H2O in EA, compound 13 exclusively fur-
nished aromatized product (45) (Table 4). Others Lewis acids such
as Sc(OTf).3xH2O, CuCl2. 2H2O, InCl3 also led to the aromatized
product in major amounts (see SI). This susceptibility of aromati-
zation may be due to the presence of activating methoxy groups
attached to the benzene ring. As an alternative, we tried with
BINOL-derived Brønsted acids as catalysts in view of their appli-
cability in asymmetric reactions.17 After an extensive optimization
study (see SI), 10 mol% BINOL-derived phosphoric acid (BINOL-
PO2H) in CHCl3 at rt was found to be the best for 13 affording ene
product 53 in 80% yield, although it took 5 days for completion of
the reaction (Table 4). Like 13, the ene reactions of substrates 14 and
27 in the presence of SnCl4$5H2O in EA resulted in exclusive for-
mation of aromatized products 54 and 55. On contrary, under the
influence of BINOL-derived phosphoramide (BINOL-PONHTf) the
reaction afforded some nonaromatized products. However, these
products 56 and 57 appeared to form from dimerization of the
initial ene products as proposed in the mechanism (vide SI) (Table
4).
Optimization studies for intramolecular-ene reaction of 10e42a,b
Solvent
Ratio of 42: 43
Time
%yield
Toluene
Chloroform
DCM
Diethyl ether
Ethyl acetate
1,4-Dioxane
Acetone
0: 100
81: 19
45: 55
85: 15
90: 10
0: 100
50: 17
1.5 d
3.5 h
2 h
91
85
89
89
91
83
55c
4 d
1.5 d
3.5 d
3 dc
a
Ratio of the products was determined by 1H NMR analysis.
All reactions were carried out with 50 mol% SnCl4$5H2O at rt.
33% starting aldehyde recovered.
b
c
ene product 47 in 86% yield with a small amount of aromatized
product 4815 (7%). These conditions worked well with naphthalene
substrates 15 and 16 affording ene products 49 and 50 in 85% and
88% yield respectively along with aromatized products 51 and 46
respectively. Thus the above conditions are well-suited for unsub-
stituted aromatic aldehyde precursors 10, 11, 15, 16. Incorporation
of a single methoxy group in the benzene nucleus as in 12 did not
alter the course of the ene cyclization. When it was treated under
optimized conditions, the expected ene product 52 was obtained in
78% yield along with aromatized product 44 as the minor product
(Table 3).
Compounds 14 and 27 are more susceptible to aromatization
than 13. This can be explained by considering destabilaization of
incipient carbocation 58 due to peri-effect of the methoxy group
with the indicated hydrogen (Scheme 5).
When 32 was treated with SnCl4$5H2O in ethyl acetate, ex-
pected ene product 59 was not obtained. Instead, anthracene
derivatives 60 and 61 were obtained. The compound 60 seemed
Since peri-oxygenated hydroaromatics commonly occur in many
naturally occurring quinones,16 we evaluated ICE reaction of few
Table 3
ICE reaction of ortho propenyl aromatic carboxaldehydes with 50 mol% SnCl4$5H2O, EA at room temperature
Substrates Non-aromatized ene products (%yield) Aromatized ene products (%yield)
Time
1.5 d
1.5 d
1.5 d
1.5 d
2 d

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S. Basak, D. Mal / Tetrahedron 72 (2016) 1758e1772
Table 4
Optimized conditions of ICE reactions of substrates having aromatic methoxy groups
Our next objective was to evaluate the reactivity of a polar-
ized carbonecarbon double bond as an enophile in the ene re-
action. Treatment of the alkylidene malonate 39 with
SnCl4$5H2O, provided a 42:49 mixture of 43 and 65. It was inert
to BINOL-derived phosphoric acid. No reaction of 39 took place
even at elevated temperature (up to 100 ꢀC). However, BINOL-
PONHTf promoted the reaction, but it was very slow at room
temperature. When it was conducted at 80 ꢀC, the reaction was
complete in 3 d giving 65 in 94% yield. However, substrate 40
with an acrylate functionality, resisted cyclization with catalysts
like SnCl4$5H2O or BINOL-PO2H. With BF3$OEt2 in DCM, it un-
derwent intramolecular RauhuteCurrier like reaction resulting in
a mixture of products 66 (35%) and 67 (57%). This type of cycli-
zation has some resemblance with recent publication on for-
mation of five-membered ring.18a Formation of hydrolysed
product 67 was confirmed by transforming it into its methyl
ester derivative by DBU-MeI.18b
O
O
O
O
O
O
-H3O+
H
O
OH
O
H
O
13
53 (80%)
58
45 (15%)
Scheme 5. Explanation for the differential reactivities of 13, 14 and 27.
to form via aromatization of putative ICE product 59, which could
not be isolated. Formation of the anthraquinone 61 is interesting
and unprecedented (vide SI). It was obtained as the sole product
with 10 mol% BINOL-PO2H in CHCl3 at room temperature
(Table 5).
Formation of the abnormal product 61 can be explained by the
mechanism shown in Scheme 6. The aromaized ene product 60
acting as a photosensitizer forms singlet oxygen and then reacts
with it to form cycloaddition adduct 62. Fragmentation of 62 forms
a bisoxocarbenium ion 63, which upon reaction with moisture
furnishes 64. Elimination of methanol from 64 gives 61.
In view of extending scope of the ICE reaction to formation of
a five-membered ring, substrate 41 was treated under 10 mol%
BINOL-PONHTf.19 Within 1 d at room temperature, it gave indenol
68 in 96% yield (Table 6).

S. Basak, D. Mal / Tetrahedron 72 (2016) 1758e1772
1763
Table 5
ICE reaction of 32, an intermediate for the synthesis of Altersolanol-p
Substrates
Products (%yield)A,B
A: 50 mol% SnCl4$5H2O, ethyl acetate, rt, 1 d.; B: 10 mol% BINOL-PO2H, CHCl3, rt, 4 d.
Brønsted acid
catalyst
CHCl3, rt
O
O
O
*
O2 O2
hν
CHO
O
O
OH
O
O
O
O
32
59
60 (photosensitizer)
OH2
H
H
O
O
O
O
O
O
H
H
O
O
O
O
CH3OH
O
O
O
O
O
O2
OH2
62
63
64
61
Scheme 6. Proposed mechanism for the formation of 61.
Table 6
ICE reaction of ene precursors containing an olefinic double bond
2.4. Elaboration of ICE product 42
double bond of the ene products without aromatization of the new
cyclohexane ring was envisaged for facile entry to altersolanol P (3)
and aranciamycin I (6). Since 42 is readily aromatized in acidic
conditions, it was derivatized to its acetate 69 with Ac2O-pyridine.
However, the acetate 69 slowly decomposed on standing.
With a view to paving the synthetic route to altersolanol P (3),
galtamycinone (4) and aranciamycin I (6), few model elaborations
were briefly studied. Regioselective transposition of the exocyclic

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S. Basak, D. Mal / Tetrahedron 72 (2016) 1758e1772
Alternatively, ene product 42 was silylated with TBSCl-imidazole to
give ether 70. Transposition of the double bond in 70 was initially
attempted with BF3$Et2O and TsOH. But, none were successful.
However, on reaction with [Rh(PPh3)3Cl] and DBU (10 equiv), 70
smoothly isomerized to 71 without any aromatization.20 For ep-
oxidation of 71 to 72, a few standard epoxidations with m-CPBA
were attempted. The best procedure was Oxone based method.21
When treated with Oxone, sodium bicarbonate in acetone, H2O,
EA (5:1:1), compound 71 delivered epoxide 72 in 70% yield. The
relative stereochemistry of the cyclohexane ring of 72 was estab-
lished by analysis of coupling constants and a NOESY experiment.
As a model study on the A ring formation of galtamycinone (4),
which features an m-cresol unit, tetralin 42 was submitted to PDC
FTIR instrument using a KBr pellet. The phrase ‘usual work-up’ or
‘worked up in the usual manner’ refers to washing of the organic
phase with water (2ꢁ1/4 of the volume of the organic phase) and
brine (1ꢁ1/4 of the volume of the organic phase), drying (Na2SO4),
filtration, and concentration under reduced pressure.
3.2. Preparation of the ene-precursors
3.2.1. General procedure to prepare ene-substrate from different 2-
formylphenylboronic acids.9b To a solution of methallyl bromide
(2 equiv) in THF (0.2 M) in a two neck round bottom flask were
added PdCl2(PPh3)2 (2.5 mol%) and aq Na2CO3 (1 M, 2 equiv). This
solution was degassed with inert gas. To this, a degassed solution of
2-formylphenylboronic acid (0.25 equiv) was added and the
resulting mixture was heated at reflux. After 1 h, the reaction
mixture was cooled to rt, and another 0.25 equiv degassed solution
of the boronic acid was added. After 6e7 h, the reaction mixture
was cooled and quenched with water (3 mL/mmol) and extracted
with DCM (3ꢁ10 mL/mmol). The combined organic layer was
washed with brine, dried over MgSO4, and concentrated under
vacuum. The residue was purified by flash column chromatography
on silica gel.
in DCM. The desired oxidized product a-naphthol 73 was obtained.
On the contrary, when it was treated with PCC in DCM, it gave
unexpectedly menadione (74), perhaps resulting from over-
oxidation of possible alkylidene ketone 75 (Scheme 7).22
Oxone, acetone,
water, ethyl acetate
rt, 45 min
RhCl(PPh3)3 (10 mol%)
DBU, EtOH, reflux
10 d
O
69%
73%
OTBS
OTBS
OR
69 R = COCH3
70 R = TBS
71
72
3.2.2. 2-(2-Methallyl)benzaldehyde (10).9b,9c General procedure A
was followed for coupling between 2-formylphenylboronic acid
(2.050 g,13.67 mmol) and methallyl bromide (3.663 g, 27.33 mmol).
The crude product was purified by flash column chromatography
on silica gel with hexane to afford the desired product 10 (1.554 g,
9.70 mmol) in 71% yield and unwanted yellowish, liquid [1,10-Bi-
phenyl]-2,20-dicarboxaldehyde (0.689 g, 3.28 mmol) in 24% yield.
PDC, DCM, rt
83%
OH
OH
42
73
PCC, DCM, rt
81%
O
O
O
74
3.2.3. Data for 10. Yellowish liquid; Rf (hexane) 0.5; 1H NMR
75
(400 MHz, CDCl3):
d
10.25 (s, 1H), 7.87 (dd, J¼1.0, 7.6 Hz, 1H), 7.53
Menadione (Vit K3)
(dt, J¼1.0, 7.6 Hz, 1H), 7.39 (t, J¼7.6, 1H), 7.28 (d, J¼7.6 Hz, 1H), 4.84
Scheme 7. Functional group modifications of ene product 42.
(s, 1H), 4.46 (s, 1H), 3.74 (s, 2H), 1.78 (s, 3H); 13C NMR (100 MHz,
CDCl3): d 192.3 (CH), 145.4,142.3,134.6,134.0 (CH), 131.8 (CH), 130.8
(CH), 127.2 (CH), 112.7 (CH2), 40.4 (CH2), 23.1 (CH3).
3. Conclusion
3.3. Preparation of ethallyl bromide23
We have successfully developed an efficient synthesis of o-
methallylbenzaldehyde and demonstrated their utilities in intra-
molecular carbonyl-ene reaction to provide a regiodefined syn-
thesis of oxygenated hydroaromatics. In this study, we have
reported synthesis of hydroaromatics containing anthracene,
phenanthrene and naphthacene nuclei. Isolation of the non-
aromatized ene products is delicately sensitive to the nature of
substituents, catalysts and reaction conditions. Peri-effects seem to
play important roles to prevent dehydrative aromatization of the
products. This fact will be under further scrutiny. Ene products are
amenable to useful functionalizations especially transposition of
the new double bond. Studies on the total synthesis of altersolanol
P (3), aranciamycin I (6) etc. are underway.
3.3.1. 2-Methylenebutyraldehyde. This was prepared according to
the literature procedure. 1H NMR (400 MHz, CDCl3):
d 9.46 (s, 1H),
6.17 (s, 1H), 5.91 (s, 1H), 2.17 (q, J¼7.6 Hz, 2H), 0.98 (t, J¼7.6 Hz, 3H);
13C NMR (100 MHz, CDCl3):
(CH2), 11.9(CH3).
d 194.8 (CH), 151.8, 133.2 (CH2), 20.9
3.3.2. 2-Methylenebutan-1-ol. To a stirred solution of 2-methylene-
butyraldehyde (3.7 g, 44 mmol) in MeOH (50 mL) was added
CeCl3$7H2O (19.7 g, 53 mmol). Then NaBH4 (2.01 g, 53 mmol) was
added portion wise and reaction mixture was stirred for 3.0 h.
MeOH was evaporated under vacuum. Usual work-up of the mix-
ture using diethyl ether afforded 2-methylenebutan-1-ol (2.70 g,
31.4 mmol) in 71% yield. Colourless liquid; 1H NMR (200 MHz,
3.1. Experimental section
CDCl3): d 4.97 (s, 1H), 4.83 (s, 1H), 4.03 (s, 2H), 2.37 (bs, 1H), 2.04 (q,
J¼7.4 Hz, 2H), 1.03 (t, J¼7.4 Hz, 3H); 13C NMR (50 MHz, CDCl3):
All reactions utilizing moisture-sensitive reagents were per-
formed under an inert atmosphere. All solvents namely DMF, DCM,
THF, MeOH etc. were dried prior to use, according to the standard
protocols. Melting points were determined in open capillary tubes
and are reported as uncorrected. TLC was carried out on precoated
plates (silica gel 60 F254), and the spots were visualized with UV and
fluorescent lights. Column chromatography was performed on sil-
ica gel (60e120 or 230e400 mesh). 1H and 13C NMR spectra for all
the compounds were recorded at 200/400/600 and 50/100/
150 MHz (Bruker AVANCE 200, Bruker UltrashieldÔ 400, AscendÔ
600), respectively. IR spectra were recorded with a PerkineElmer
d 150.8, 108.1 (CH2), 65.9 (CH2), 25.8 (CH2), 12.2 (CH3).
3.3.3. 2-Bromomethyl-but-1-ene. 2-Bromomethyl-but-1-ene was
prepared from 2-methylene-butan-1-ol following the reported
procedure. 1H NMR (200 MHz, CDCl3):
d 5.14 (s, 1H), 4.94 (s, 1H),
3.97 (s, 2H), 2.22 (q, J¼7.4 Hz, 2H), 1.06 (t, J¼7.4 Hz, 3H); 13C NMR
(50 MHz, CDCl3):
(CH3).
d 147.3, 114.0 (CH2), 37.1 (CH2), 26.4 (CH2), 12.1
3.3.4. 2-(2-Methylenebutyl)benzaldehyde (11). General procedure A
was followed for coupling between 2-formylphenylboronic acid

S. Basak, D. Mal / Tetrahedron 72 (2016) 1758e1772
1765
(1.025 g, 6.80 mmol) and ethallylbromide (2.022 g, 13.66 mmol).
The crude was purified by flash column chromatography on silica
gel with hexane to afford the desired product 11 (1.120 g,
5.00 mmol) in 73% yield, unwanted yellowish liquid [1,10-Biphenyl]-
2,20-dicarboxaldehyde (0.214 g, 1.02 mmol) in 15% yield.
(CH3); Data for hemiacetal form 21. 1H NMR (400 MHz, DMSO-d6)
d
8.83 (s, 1H), 6.97 (d, J¼8.8 Hz, 1H), 6.82 (d, J¼8.8 Hz, 1H), 6.71 (d,
J¼8.4 Hz, 1H), 6.07 (d, J¼8.4 Hz, 1H), 3.71 (s, 3H).
3.3.10. 3,6-Dimethoxy-2-(2-methallyl)benzaldehyde (13). Coupling
reaction between mixture of boronic acid 20 and its hemiactal form
21 (0.420 g, 2.00 mmol) and methallyl bromide (0.535 g,
4.00 mmol) was performed following the general procedure A. The
crude product was purified by flash column chromatography on
silica gel with 1:20 EA/hexane solvent to afford the desired yel-
lowish liquid product 13 (0.352 g, 1.60 mmol) in 80% yield. Rf (1:20
3.3.5. Data for 11.9d Yellowish liquid; Rf (1:20 EA/hexane) 0.4; 1H
NMR (200 MHz, CDCl3):
d
10.23 (s, 1H), 7.77 (dd, J¼1.2, 7.4 Hz, 1H),
7.53 (dt, J¼1.6, 7.4 Hz, 1H), 7.39 (t, J¼7.4 Hz, 1H), 7.28 (d, J¼7.4 Hz,
1H), 4.85 (d, J¼1.2 Hz,1H), 4.41 (d, J¼1.2 Hz,1H), 3.75 (s, 2H), 2.10 (q,
J¼7.4 Hz, 2H), 1.08 (t, J¼7.4 Hz, 3H); 13C NMR (50 MHz, CDCl3):
d
192.3 (CH), 151.2, 142.5, 134.5, 134.0 (CH), 131.9 (CH), 130.6 (CH),
EA/hexane) 0.3; 1H NMR (200 MHz, CDCl3):
d 10.52 (s, 1H), 7.07 (d,
127.1 (CH), 110.7 (CH2), 39.0 (CH2), 29.5 (CH2), 12.4 (CH3); HRMS
(ESI): m/z calculated for C12H14O: requires: 175.1123 for [MþH]þ,
157.1017 for [MꢂH2OþH]þ; found: 175.1129, 157.1040.
J¼9.0 Hz, 1H), 6.84 (d, J¼9.0 Hz, 1H), 4.64 (q, J¼1.8 Hz, 1H),
4.31e3.98 (m, 1H), 3.86 (s, 3H), 3.79 (s, 3H), 3.71 (s, 2H), 1.90e1.65
(m, 3H); 13C NMR (50 MHz, CDCl3):
d 192.6 (CH), 157.0, 152.3, 145.5,
131.8,124.8,117.5 (CH),110.2 (CH),109.3 (CH), 57.0 (CH3), 56.4 (CH3),
32.8 (CH2), 23.8 (CH3); nmax (KBr, cmꢂ1): 2938, 1687, 1592, 1477,
1263, 1085, 887, 717; HRMS (ESI): m/z calculated for C13H16O3: re-
quires: 221.1178 for [MþH]þ; found: 221.1180.
3.3.6. 2-formyl-4-methoxyphenylboronic acid (18) and its hemiacetal
form 19.10a,10b Mixture of boronic acid 18 and its hemiacetal 19 was
prepared according to the literature procedure. Peaks of 18 were
only detectable from the spectra.
3.3.11. Boronic acid 22. 10cLiterature procedure was followed to
prepare the boronic acid 22. Dark brown crystal; mp 96e98 ꢀC; 1H
3.3.7. Data for 18. 1H NMR (400 MHz, DMSO-d6)
7.62 (d, J¼8.4 Hz, 1H), 7.38 (d, J¼2.8 Hz, 1H), 7.19 (dd, J¼2.8, 8.4 Hz),
3.81 (s, 3H); 13C NMR (100 MHz, DMSO-d6)
194.9 (CH), 160.7,
d 10.22 (s, 1H),
NMR (400 MHz, CDCl3) d 9.77 (s,1H), 8.22e7.86 (m, 2H), 7.81 (s,1H),
d
7.37 (s, 1H), 4.02 (d, J¼16.2 Hz, 6H); 13C NMR (100 MHz, CDCl3)
142.1, 136.3 (CH), 119.8 (CH), 113.2 (CH), 55.9 (CH3).
d 196.8 (CH), 153.5, 150.6, 133.8, 121.0 (CH), 120.9 (CH), 56.5 (CH3),
56.3 (CH3). 11B NMR (128 MHz, CDCl3):
d 28.2.
3.3.8. Data for 5-methoxy-2-(2-methallyl)benzaldehyde (12).9e
General procedure A was performed on mixture of boronic acid
18 and its hemiacetal 19 (0.567 g, 3.15 mmol) and methallyl bro-
mide (0.844 g, 6.30 mmol). The reaction mixture was purified by
flash column chromatography on silica gel (1:10 EA/hexane) to
afford the desired colourless product 12 (0.360 g, 1.89 mmol) in
60% yield along with the dimeric product [4,40-dimethox-
ybiphenyl]-2,20-dicarboxaldehyde24 (0.270 g, 0.54 mmol) in 17%
3.3.12. 4,5-Dimethoxy-2-(2-methallyl)benzaldehyde (14). General
procedure A was performed on 22 (0.577 g, 2.75 mmol) and
methallyl bromide (0.737 g, 5.50 mmol). The crude product was
purified by flash column chromatography on silica gel with 1:15 EA/
hexane to afford the desired product 14 (0.430 g, 1.95 mmol) in 71%
yield along with dimeric product [4,5,40,50-Tetramethoxybiphenyl]-
2,20-dicarboxaldehyde in (0.091 g, 0.28 mmol) 10% yield.
yield. Rf (1:10 EA/hexane) 0.4; 1H NMR (400 MHz, CDCl3):
d 10.22
(s, 1H), 7.39 (d, J¼2.8 Hz, 1H), 7.17 (d, J¼8.4 Hz, 1H), 7.08 (dd, J¼2.8,
3.3.13. Data for 14. Colourless liquid; Rf (1:15 EA/hexane) 0.45; 1H
8.4 Hz, 1H), 4.82 (s, 1H), 4.44 (s, 1H), 3.85 (s, 3H), 3.64 (s, 2H), 1.76
NMR (400 MHz, CDCl3):
(s, 1H), 4.49 (s, 1H), 3.93 (s, 3H), 3.92 (s, 3H), 3.65 (s, 2H), 1.76 (s,
3H); 13C NMR (50 MHz, CDCl3):
190.0 (CH), 154.0, 148.2, 145.5,
d 10.14 (s, 1H), 7.40 (s, 1H), 6.70 (s, 1H), 4.84
(s, 3H); 13C NMR (100 MHz, CDCl3):
d 191.7 (CH), 158.7, 145.8, 135.2,
134.9, 133.0 (CH), 121.3 (CH), 112.7 (CH), 112.6 (CH2), 55.7 (CH3),
39.5 (CH2), 23.0 (CH3).
d
137.6, 127.6, 113.6 (CH), 112.8 (CH2), 110.54 (CH), 56.3 (CH3), 56.2
~
(CH3), 39.7 (CH2), 22.9 (CH3); IR (KBr): v¼3447, 2931, 1676, 1597,
3.3.9. Boronic acid 20 and 21.25 2-(2,5-dimethoxy phenyl)-1,3-
dioxane (1.120 g, 5.00 mmol) was dissolved in hexane (34 mL)
and the reaction was cooled to ꢂ25 ꢀC. To the cooled solution was
added freshly distilled benzene (11 mL) followed by drop wise
addition of n-BuLi (1.6 M, 5.3 mL, 8.50 mmol). After 12 h, trime-
thylborate (2.2 mL, 9.35 mmol) in THF (11.2 mL) was added and the
reaction was stirred at the same temperature for 2 h. Then it was
allowed to warm to rt and stirred for 12 h. The reaction mixture was
quenched with 2 (M) HCl (7.5 mL) and stirred for 3 h. It was then
extracted with EA (3ꢁ50 mL). Solvent was evaporated. Crude ma-
terial was dissolved in 2 (M) NaOH (10 mL) and was thoroughly
washed with ether (3ꢁ10 mL). Aqueous part was acidified with
conc. HCl to pH 2e3. This was extracted with EA (3ꢁ25 mL). The
combined organic layers was dried over Na2SO4 and evaporated to
afford a mixture of 20 and its hemiacetal form 21 (4:1) (630 mg,
3.00 mmol) in 60% yield. Yellowish solid; mp 130e135 ꢀC; 11B NMR
~
1512, 1458, 1404, 1354, 1271, 1227, 1101, 1000, 882, 757 cmꢂ1; HRMS
(ESI): m/z calculated for
C13H16O3: requires: 203.1072 for
[MꢂH2OþH]þ, 221.1178 for [MþH]þ; found: 203.1099, 221.1249.
3.3.14. 2-Formyl-1-naphthylboronic acid 23 and its hemiacetal form
24. To a stirred solution of 2-(1-bromonaphthalen-2-yl)-[1,3]di-
oxane26, (10.9 g, 37.33 mmol) in dry THF (120 mL) was added n-BuLi
(2.5 (M) in hexane, 19.4 mL, 48.53 mmol) drop wise under inert
atmosphere at ꢂ78 ꢀC. The reaction mixture was stirred for 1 h.
Then B(OCH3)3 (6 mL, 53.4 mmol) was added and stirred for 2 h at
the same temperature. The resulting mixture was allowed to warm
to room temperature and stirred for 12 h. 2 M HCl (56 mL) was
added at 0 ꢀC and stirred for 3 h. The mixture was extracted with EA
(3ꢁ100 mL). Solvent was evaporated. Crude material was dissolved
in 2 M NaOH (80 mL) and was thoroughly washed with ether
(3ꢁ50 mL). The aqueous part was acidified with conc. HCl to pH
2e3. This was extracted with EA (3ꢁ10 mL). The combined organic
layers was dried over Na2SO4 and was evaporated to get mixture of
boronic acid 23 and its hemiacetal form 24 (2:1) (4.1 g, 20.5 mmol)
in 50% yield.
(128 MHz, CDCl3):
d
28.4. IR (KBr): v¼3527, 1657, 1426, 1382, 1326,
1289, 1249, 1193, 1062, 942, 714 cmꢂ1. HRMS (ESI): m/z calculated
for C9H11BO5: requires: 193.0672 for [MꢂH2OþH]þ, 233.0623 for
[MþNa]þ; found: 193.0720, 233.0623. 1H NMR signals of individual
components were predicted from 1H NMR spectrum of the mix-
ture; Data for boronic acid 20. 1H NMR (400 MHz, DMSO-d6)
3.3.15. Data for 2-(1-bromonaphthalen-2-yl)-[1,3]dioxane. 1H NMR
d
10.28 (s, 1H), 7.51 (s, 2H), 7.18 (d, J¼8.8 Hz, 1H), 7.04 (d, J¼8.8 Hz,
1H), 3.82 (s, 3H), 3.67 (s, 3H); 13C NMR (100 MHz, DMSO-d6)
190.6
(CH), 156.4, 155.4, 127.4, 119.0 (CH), 112.8 (CH), 56.7 (CH3), 56.6
(400 MHz, CDCl3):
7.52e7.62 (m, 2H), 6.12 (s, 1H), 4.30e4.34 (m, 2H), 4.07e4.14 (m,
2H), 2.25e2.37 (m, 1H), 1.46e1.50 (m, 1H); 13C NMR (100 MHz,
d
8.39 (d, J¼8.4 Hz, 1H), 7.82e7.87 (m, 3H),
d

1766
S. Basak, D. Mal / Tetrahedron 72 (2016) 1758e1772
CDCl3):
d
135.7, 135.0,132.2, 128.3 (CH), 128.2 (CH), 127.9 (CH), 127.5
J¼8.4 Hz, 1H), 7.85 (d, J¼8.0 Hz, 1H), 7.61e7.65 (m, 1H), 7.51e7.54
(m, 1H), 7.36 (d, J¼8.4 Hz, 1H), 4.90 (s, 1H), 4.50 (s, 1H), 3.82 (s, 2H),
(CH), 127.2 (CH), 124.8 (CH), 123.1 (CH), 102.2 (CH), 67.8 (2 CH2),
26.0 (CH2); IR (KBr): v¼3446, 2963, 2854, 2370, 1654, 1560, 1542,
1.81 (s, 3H). 13C NMR (100 MHz, CDCl3):
d 193.8 (CH), 145.2, 144.2,
~
1507, 1459, 1375, 1342, 1275, 1231, 1148, 1103, 995, 958, 816,
745 cmꢂ1; HRMS (ESI): m/z calculated for C14H13BrO2: requires:
295.0157 for [MþH]þ; found: 295.0187.
134.5 (CH), 133.0, 131.3, 129.6 (CH), 129.3, 129.0 (CH), 128.5 (CH),
126.5 (CH), 125.3 (CH), 113.4 (CH2), 41.2 (CH2), 23.2 (CH3). IR (KBr):
v¼2919, 1685, 1428, 1220, 1062, 893, 812, 670 cmꢂ1; HRMS (ESI): m/
~
z calculated for C15H14O: requires: 193.1017 for [MꢂH2OþH]þ,
3.3.16. Data for mixture of boronic acid 23 and its hemiacetal form
211.1123 for [MþH]þ; found: 193.1013, 211.1130.
24. Yellow solid; 11B NMR (128 MHz, DMSO-d6):
d 30.9; IR (KBr):
~
v¼3367, 3048, 1520, 1500, 1472, 1452, 1394, 1372, 1337, 1270, 1220,
3.3.21. 4-Methoxy-3-(2-methallyloxy)benzaldehyde (28). 11To a stir-
red solution of isovanillin (8.8 g, 57.9 mmol) in dry acetone
(300 mL) was added solid K2CO3 (8.0 g, 57.9 mmol) at 0 ꢀC followed
by addition of methallyl bromide (8.8 mL, 86.9 mmol). The reaction
mixture was stirred for 24 h. Acetone was evaporated. The mixture
was extracted with EA (250 mL) and the organic layer was washed
with H2O (3ꢁ100 mL) and brine (100 mL). The combined organic
layer was dried over Na2SO4 and evaporated under vacuum to af-
ford the crude material. It was purified by performing flash column
chromatography on silica gel with 1:5 EA/hexane solvent to afford
28 (10.9 g, 52.7 mmol) in 91% yield. Yellow oil; Rf (1:5 EA/hexane)
1199, 1140, 1101, 1063, 944, 733 cmꢂ1; HRMS (ESI): m/z calculated
for
C
11H9O2B: requires: 183.0617 for [MꢂH2OþH]þ; found:
183.0640. 1H NMR peaks of individual components were predicted
from 1H NMR spectrum of the mixture; Data for boronic acid 23.
1H NMR (400 MHz, DMSO-d6):
d
10.18 (s, 1H), 8.34 (d, J¼8.0 Hz, 1H),
8.06e7.54 (m, 7H); 13C NMR (100 MHz, DMSO-d6):
d
194.2 (CH),
135.9, 135.8, 134.7, 130.9 (CH), 129.3 (CH), 128.9 (CH), 128.9 (CH),
127.4 (CH), 124.8 (CH); Data for hemiacetal form 24. 1H NMR
(400 MHz, DMSO-d6):
(100 MHz, DMSO-d6):
127.6 (CH), 127.5 (CH), 126.7 (CH), 121.4 (CH), 97.8 (CH).
d
8.06e7.54 (m, 8H), 6.31 (s, 1H). 13C NMR
d
155.8, 134.3, 133.6, 132.3 (CH), 129.0 (CH),
0.55; 1H NMR (200 MHz, CDCl3)
6.91 (d, J¼8.2 Hz, 1H), 5.06 (s, 1H), 4.94 (s, 1H), 4.49 (s, 2H), 3.88 (s,
3H),1.77 (s, 3H); 13C NMR (50 MHz, CDCl3)
190.8 (CH),154.9,148.7,
d 9.75 (s, 1H), 7.41e7.32 (m, 2H),
3.3.17. 1-(2-Methallyl)naphthalene-2-carboxaldehyde (15). General
procedure A was followed to perform coupling reaction between
mixture of boronic acid 23 and its hemiacetal form 24 (0.610 g,
3.05 mmol) and methallyl bromide (0.817 g, 6.10 mmol). Reaction
mixture was purified by flash column chromatography on silica gel
with 1:25 EA/hexane solvent to afford the desired product 15
(0.320 g, 1.53 mmol) in 50% yield. Yellowish liquid; Rf (1:25 EA/
d
140.1, 130.0, 126.7 (CH), 113.2 (CH2), 111.2, 110.8 (CH), 72.5 (CH2),
~
56.1 (CH3), 19.3 (CH3); IR (KBr): v¼3422, 2936, 1686, 1611, 1582,
1508, 1438, 1270, 1220, 1162, 1134, 1017, 905, 642 cmꢂ1
.
3.3.22. [4-Methoxy-3-(2-methyl-allyloxy)phenyl]methanol (29). To
a stirred solution of compound 28 (5.15 g, 25 mmol) in THF (50 mL)
and MeOH (16 mL) at 0 ꢀC was added NaBH4 (1.04 g, 27.5 mmol) in
portions. The resulting mixture was stirred at rt for overnight. Then
it was quenched with saturated NH4Cl. Extraction of the reaction
mixture with EA (3ꢁ75 mL) followed by drying over Na2SO4 and
removal of solvent gave a residue. Flash column chromatography of
the residue on silica gel with 1:5 EA/hexane solvent afforded
product 29 (4.1 g, 19.7 mmol) in 79% yield. Colourless liquid; Rf (1:5
hexane) 0.35; 1H NMR (400 MHz, CDCl3):
d 10.52 (s, 1H), 8.14 (d,
J¼8.2 Hz, 1H), 7.97 (d, J¼8.2 Hz, 1H), 7.82e7.88 (m, 2H), 7.55e7.62
(m, 2H), 4.86 (t, J¼1.2 Hz, 1H), 4.28 (s, 1H), 4.20 (s, 2H), 1.94 (s, 3H);
13C NMR (50 MHz, CDCl3):
d 192.2 (CH), 144.8, 141.7, 136.5, 132.8,
131.9, 129.0 (CH), 128.8 (CH), 127.9 (CH), 127.1 (CH), 125.7 (CH),
~
124.0 (CH), 113.2 (CH2), 34.6 (CH2), 23.7 (CH3); IR (KBr): v¼3458,
1678, 1649, 1452, 1345, 1227, 885, 810, 763, 747 cmꢂ1; HRMS (ESI):
m/z calculated for C15H14O: requires: 193.1017 for [MꢂH2OþH]þ,
211.1123 for [MþH]þ; found: 193.1058, 211.1142.
EA/hexane) 0.45; 1H NMR (400 MHz, CDCl3)
5.07 (s, 1H), 4.95 (s, 1H), 4.51 (d, J¼2.4 Hz, 2H), 4.54 (s, 2H), 3.81 (s,
3H), 2.50 (bs, 1H), 1.80 (s, 3H); 13C NMR (50 MHz, CDCl3)
149.0,
d 6.86e6.78 (m, 2H),
d
3.3.18. 2-(2-Methallyl)-naphthalene-1-carboxaldehyde (16). A mix-
ture of boronic acid 25 and its hemiacetal 26 was prepared from 2-
(2-bromonaphthalen-1-yl)-[1,3]dioxane26 (1.460 g, 5 mmol) fol-
lowing the same process as the preparation of mixture of boronic
acid 23 and its hemiacetal form 24 from 2-(2-bromonaphthalen-1-
yl)-[1,3]dioxane. The crude product (0.68 g, w3.4 mmol) was suf-
ficiently pure to carry out the Suzuki coupling reaction with
methallyl bromide (0.91 g, 6.8 mmol) following the general pro-
cedure A. The crude product was purified by flash column chro-
matography on silica gel with 1:10, EA/hexane to afford the desired
product 16 (0.48 g, 2.3 mmol) in 68% yield along with dimerized
product [1,20-binaphthalenyl]-2,10-dicarboxaldehyde27 (0.294 g,
0.95 mmol) in 19% yield.
148.3, 140.8, 133.7, 119.8 (CH), 112.9 (CH2), 112.7 (CH), 111.8 (CH),
~
72.6 (CH2), 65.0 (CH2), 56.1 (CH3), 19.4 (CH3); IR (KBr): v¼3411,
2920, 2847, 2361, 1592, 1515, 1427, 1261, 1157, 1136, 1021, 903,
807 cmꢂ1. HRMS (ESI): m/z calculated for C12H16O3: requires:
191.1072 for [MꢂH2OþH]þ; found: 191.1080.
3.3.23. 3-Hydroxymethyl-6-methoxy-2-(2-methallyl)phenol (30). A
solution of compound 29 (3.0 g, 14.4 mmol) in DMF (15 mL) was
heated at reflux for 28 h. DMF was evaporated under reduced
pressure. Flash column chromatography of the residue on silica gel
with 1:3 EA/hexane solvent afforded 30 (1.58 g, 7.6 mmol) in 53%
yield and its ether (1.33 g, 6.5 mmol) 45% yield. White crystalline
solid; Rf (1:3 EA/hexane) 0.5; mp 82e84 ꢀC; 1H NMR (400 MHz,
CDCl3)
4.76 (s, 1H), 4.55 (s, 2H), 4.44 (s, 1H), 3.87 (s, 3H), 3.48 (s, 2H), 2.04
(bs, 1H), 1.82 (s, 3H); 13C NMR (50 MHz, CDCl3)
146.2, 145.8, 144.1,
d
6.88 (d, J¼8.0 Hz, 1H), 6.74 (d, J¼8.0 Hz, 1H), 5.89 (s, 1H),
3.3.19. Data for 2-(2-bromonaphthalen-1-yl)-[1,3]dioxane. 1H NMR
(200 MHz, CDCl3):
d
9.03 (d, J¼8.2 Hz, 1H), 7.79 (d, J¼8.2 Hz, 1H),
d
7.47e7.69 (m, 4H), 6.55 (s, 1H), 4.39 (dd, J¼4.6, 11.2 Hz, 2H), 4.12 (t,
133.1, 123.9, 120.1 (CH), 110.2 (CH2), 108.5 (CH), 63.4 (CH2), 56.1
J¼11.6 Hz, 2H), 2.38e2.63 (m, 1H), 1.54 (d, J¼13.6, 1H); 13C NMR
(CH3), 33.5 (CH2), 23.1 (CH3); IR (KBr): v¼3434, 3185, 1618, 1491,
~
(50 MHz, CDCl3):
d
133.7, 132.3, 132.0, 131.1 (CH), 130.0 (CH), 128.3
1440, 1272, 1090, 890, 792 cmꢂ1; HRMS (ESI): m/z calculated for
(CH), 126.9 (CH), 126.7 (CH), 126.3 (CH), 122.0, 105.0 (CH), 68.3 (2
C
12H16O3: requires: 191.1072 for [MꢂH2OþH]þ, 381.2066 for
~
CH2), 26.2 (CH2). IR (KBr): v¼3458, 2967, 2852, 1636, 1413, 1370,
[(MꢂH2O)2þH]þ; found: 191.1080, 381.2052.
1144, 1120, 1104, 997, 947, 809, 776, 745, 469 cmꢂ1. HRMS (ESI): m/z
calculated for
C
15H14O: requires: 193.1017 for [MꢂH2OþH]þ,
3.3.24. [3,4-Dimethoxy-2-(2-methyl-allyl)-phenyl]methanol (31). To
a stirred solution of compound 30 (0.370 mg, 1.78 mmol) in acetone
(20 mL) were added potassium carbonate (1.23 g, 8.9 mmol) and
MeI (0.34 mL, 5.34 mmol). The reaction mixture was stirred for
48 h. Usual work-up was done with EA. Flash column
211.1123 for [MþH]þ; found: 193.1058, 211.1142.
3.3.20. Data for 16. Yellowish liquid; Rf (1:10 EA/hexane) 0.4; 1H
NMR (400 MHz, CDCl3):
d
10.80 (s, 1H), 9.04 (d, J¼8.8, 1H), 7.98 (d,

S. Basak, D. Mal / Tetrahedron 72 (2016) 1758e1772
1767
chromatography of the crude product on silica gel with 1:5 EA/
hexane solvent afforded product 31 (0.392 g, 1.88 mmol) in 99%
yield. White solid; Rf (1:5 EA/hexane) 0.4; mp 46e48 ꢀC; 1H NMR
NMR (400 MHz, CDCl3):
d
12.18 (s, 1H), 7.88 (d, J¼8.4 Hz, 1H), 7.52
(d, J¼8.4 Hz, 1H), 7.12 (s, 1H), 6.94 (d, J¼7.6 Hz, 1H), 5.20 (s, 1H),
5.04 (s, 1H), 4.54 (s, 2H), 4.03 (s, 3H), 3.97 (s, 3H), 1.91 (s, 3H); 13C
(400 MHz, CDCl3)
(s, 1H), 4.50 (s, 2H), 4.31 (s, 1H), 3.83 (s, 3H), 3.76 (s, 3H), 3.42 (s,
2H), 2.21 (bs, 1H), 1.81 (s, 3H); 13C NMR (50 MHz, CDCl3)
152.3,
d
7.07 (d, J¼8.4 Hz,1H), 6.78 (d, J¼8.4 Hz,1H), 4.73
NMR (100 MHz, CDCl3): d 171.3, 159.0, 157.1, 146.2, 141.2, 132.8,
129.7 (CH), 116.9, 114.9 (CH), 112.9 (CH2), 107.5 (CH), 105.2, 103.9
(CH), 72.4 (CH2), 56.6 (CH3), 52.5 (CH3), 19.9 (CH3); IR (KBr):
d
v¼3380, 2936, 1654, 1364, 1253, 1070, 772 cmꢂ1; HRMS (ESI): m/z
~
147.5, 146.2, 132.7, 131.9, 124.4 (CH), 110.5 (CH2), 110.3 (CH), 63.1
(CH2), 60.8 (CH3), 55.7 (CH3), 33.6 (CH2), 22.4 (CH3); IR (KBr):
calculated for C17H18O5: requires: 303.1232 for [MþH]þ; found:
v¼3393, 2935, 1490, 1452, 1274, 1220, 1084, 1023, 889 cmꢂ1; HRMS
303.1238.
~
(ESI): m/z calculated for
C13H17O2: requires: 205.1229 for
[MꢂH2OþH]þ; found: 205.1205.
3.3.28. Methyl 1,8-dimethoxy-4-(2-methyl-allyloxy)-naphthalene-2-
carboxylate (36). To a stirred solution of compound 35 (190 mg,
0.63 mmol) in THF (5 mL) was added NaH (60% in oil, 75.6 mg,
1.83 mmol) at 0 ꢀC followed by addition of Me2SO4 (0.5 mL,
5.04 mmol). The reaction mixture was stirred for 12 h. Then it
was quenched with H2O and the reaction mixture was extracted
with ethyl acetate (3ꢁ25 mL). Combined organic layers was
washed with H2O (2ꢁ25 mL) and brine (1ꢁ25 mL). Organic layer
was dried over Na2SO4. Triethylamine (0.44 mL, 3.15 mmol) was
added to it and stirred for 30 min. Then this solution was washed
with 1 (N) HCl solution (1ꢁ25 mL) followed by washing with
(1ꢁ25 mL) brine solution. Organic layer was dried over Na2SO4
and evaporated under vacuum to afford the crude product. Flash
column chromatography was done on silica gel with 1:10 (EA/
hexane) solvent to afford 36 (169 mg, 0.54 mmol) in 85% yield.
Colourless liquid; Rf (1:10 EA/hexane) 0.45; 1H NMR (600 MHz,
3.3.25. Preparation of 3,4-dimethoxy-2-(2-methallyl)benzaldehyde
(27). To a stirred solution of 31 (0.353 g, 1.6 mmol) in dry DCM
(10 mL) was added activated MnO2 (0.910 g, 16.0 mmol). The re-
action mixture was stirred for 4 d and filtered. Removal of the
solvent followed by flash column chromatography on silica gel with
1:10 EA/haxane afforded 27 (0.335 g, 1.52 mmol) in 95% yield. Rf
(1:10 EA/hexane) 0.5; 1H NMR (400 MHz, CDCl3)
d 9.98 (s, 1H), 7.65
(d, J¼8.4 Hz,1H), 6.70 (d, J¼8.4 Hz,1H), 4.74 (t, J¼1.2 Hz,1H), 4.24 (s,
1H), 3.91 (s, 3H), 3.77 (s, 3H), 3.73 (s, 2H), 1.83 (s, 3H); 13C NMR
(50 MHz, CDCl3)
d 190.9 (CH), 157.6, 147.5, 145.8, 136.3, 128.4, 128.0
(CH), 111.2 (CH2), 110.1 (CH), 61.1 (CH3), 55.9 (CH3), 32.3 (CH2), 23.6
~
(CH3); IR (KBr): v¼2919, 2849, 1686, 1589, 1490, 1456, 1282, 1258,
1078, 890, 809 cmꢂ1; HRMS (ESI): m/z calculated for C13H16O3:
requires: 221.1178 for [MþH]þ; found: 221.1168.
CDCl3):
d
7.93 (dd, J¼1.1, 8.4 Hz, 1H), 7.47 (t, J¼8.1 Hz, 1H), 7.10 (s,
3.3.26. Methyl 1,4-dihydroxy-8-methoxynaphthalene-2-carboxylate
(34). A solution of 3-cyanophthalide 33 (189 mg, 1 mmol) in
dry THF (5 mL) was added to stirred suspension of LTB (240 mg,
3 mmol) in dry THF (15 mL) at ꢂ60 ꢀC under an inert atmosphere.
The resulting solution was stirred at ꢂ60 ꢀC for 30 min after
which a solution of methyl acrylate (0.18 mL, 2 mmol) in dry THF
(5 mL) was added. The reaction mixture was stirred for another
30 min at ꢂ60 ꢀC followed by 6e8 h stirring at room tempera-
ture. The reaction was then quenched with saturated ammonium
chloride solution and THF was evaporated under reduced pres-
sure. The residue was then extracted with ethyl acetate
(3ꢁ20 mL). The combined extracts were washed with brine (3ꢁ1/
3 vol), dried (Na2SO4) and concentrated to afford crude product.
This crude product was purified by column chromatography on
silica gel with ethyl acetateepetroleum ether (1:3) as solvent to
obtain pure compound 34 in 95% yield (236 mg, 0.95 mmol).
Yellow solid; Rf (1:3 EA/hexane) 0.55; mp 175e176 ꢀC; 1H NMR
1H), 6.95 (d, J¼7.7 Hz, 1H), 5.20 (s, 1H), 5.05 (s, 1H), 4.59 (s, 2H),
4.00 (s, 3H), 3.95 (s, 3H), 3.88 (s, 3H), 1.91 (s, 3H); 13C NMR
(100 MHz, CDCl3):
d 167.8, 157.4, 151.9, 150.2, 140.9, 131.2, 128.1
(CH), 121.1, 121.0, 115.0 (CH), 113.0 (CH2), 107.9 (CH), 105.7 (CH),
72.4 (CH2), 63.7 (CH3), 56.5 (CH3), 52.5 (CH3), 19.8 (CH3); IR (KBr):
~
v¼2926, 2853, 2369, 1724, 1586, 1364, 1220, 1178, 1070, 1009, 902,
667 cmꢂ1; HRMS (ESI): m/z calculated for C18H20O5: requires:
317.1389 for [MþH]þ, 285.1127 for [MꢂCH3OHþH]þ; found:
317.1392, 285.1117.
3.3.29. Methyl 1,4,8-trimethoxy-3-(2-methallyl)naphthalene-2-
carboxylate (37). 33Stirred solution of compound 36 (150 mg,
0.47 mmol) in 2.5 mL DMF was refluxed for 12 h at 180 ꢀC. DMF was
evaporated under vacuum and dissolved in ethyl acetate (100 mL).
It was then washed with brine solution (5ꢁ20 mL). Combined or-
ganic layers were washed with brine solution and dried over
Na2SO4. Solvent was evaporated under vacuum to afford the crude
product. Without purification, crude material was dissolved in dry
acetone (5 mL). K2CO3 (324 mg, 2.35 mmol) was added to it at 0 ꢀC
followed by addition of Me2SO4 (0.13 mL, 1.41 mmol). The reaction
mixture was refluxed for 12 h. Acetone was evaporated reaction
mixture was extracted with ethyl acetate (3ꢁ25 mL). Combined
organic layers was washed with H2O (2ꢁ25 mL) and brine
(1ꢁ25 mL). Organic layer was dried over Na2SO4. Triethylamine
(0.33 mL, 2.35 mmol) was added to it and stirred for 30 min. Then
this solution was washed with 1 (N) HCl solution (1ꢁ25 mL) fol-
lowed by washing with (1ꢁ25 mL) brine solution. Organic layer was
dried over Na2SO4. Crude product was obtained after evaporation of
ethyl acetate under vaccum. Flash column chromatography was
done on silica gel with 1:10 EA/hexane solvent to afford 37 (108 mg,
0.33 mmol) in 70% yield. Colourless liquid; Rf (1:10 EA/hexane) 0.5;
(400 MHz, DMSO-d6):
d 11.45 (s, 1H), 9.70 (bs, 1H), 7.67 (d,
J¼8.4 Hz, 1H), 7.51 (t, J¼8.4 Hz, 1H), 7.12 (s, 1H), 7.01 (d, J¼7.6 Hz,
1H), 3.91 (s, 3H), 3.88 (s, 3H); 13C NMR (100 MHz, DMSO-d6):
d
170.7, 158.9, 154.7, 145.0, 131.8, 129.8 (CH), 116.5, 115.1 (CH),
107.9 (CH), 106.4 (CH), 106.3, 56.7 (CH3), 53.0 (CH3); IR (KBr):
~
v¼3414, 1636, 1438, 1364, 1289, 1251, 1192, 1114, 1042, 984, 806,
750 cmꢂ1; HRMS (ESI): m/z calculated for C13H13O5: requires:
249.0763 for [MþH]þ, 217.0486 for [MꢂCH3OHþH]þ; found:
249.0747, 217.0486.
3.3.27. Methyl
1-hydroxy-8-methoxy-4-(2-methyl-allyloxy)naph-
thalene-2-carboxylate (35). To a stirred solution of compound 34
(0.496 g, 2 mmol) in acetone (15 mL) was added K2CO3 (1.38 g,
10 mmol) at 0 ꢀC and stirred for 5 min followed by addition of
methallyl bromide (0.4 mL, 4 mmol) at 0 ꢀC. The reaction mixture
was warmed to rt and stirred for overnight. Acetone was evapo-
rated. The reaction mixture was extracted with 100 mL ethyl ac-
etate and was successively washed with (3ꢁ25 mL) H2O and brine
(1ꢁ50 mL). Organic layer was dried over Na2SO4 and evaporated to
afford crude product. Flash column chromatography on silica gel
was carried out with 1:5 EA/hexane solvent to furnish 35 (0.332 g,
1.10 mmol) in 55% yield. Yellow oil; Rf (1:5 EA/hexane) 0.35; 1H
1H NMR (400 MHz, CDCl3):
d
7.69 (d, J¼8.4 Hz, 1H), 7.46 (t, J¼8.0 Hz,
1H), 6.89 (d, J¼7.6 Hz, 1H), 4.81 (s, 1H), 4.55 (s, 1H), 4.00 (s, 3H),
3.87e3.83 (m, 9H), 3.54 (s, 2H), 1.74 (s, 3H); 13C NMR (100 MHz,
CDCl3):
d 168.7, 156.9, 150.6, 150.4, 143.9, 131.9, 127.6 (CH), 127.3,
126.2, 119.7, 115.3 (CH), 112.1 (CH2), 106.5 (CH), 64.1 (CH3), 62.3
(CH3), 56.3 (CH3), 52.2 (CH3), 35.2 (CH2), 22.9 (CH3); IR (KBr):
~
v¼2933, 2842, 1726, 1573, 1448, 1371, 1341, 1272, 1251, 1190, 1072,
1048, 891 cmꢂ1; HRMS (ESI): m/z calculated for C19H22O5: requires:

1768
S. Basak, D. Mal / Tetrahedron 72 (2016) 1758e1772
331.1546 for [MþH]þ, 353.1365 for [MþNa]þ, 299.1283
[MꢂMeOHþH]þ; found: 331.1543, 353.1367, 299.1283.
chromatography with silica gel and 2% EA in pet ether solvent
afforded compound 40 (350 mg,1.52 mmol) in 87% yield. Colourless
liquid; Rf (1:50 EA/hexane) 0.3; 1H NMR (400 MHz, CDCl3)
d 7.98 (d,
3.3.30. 1,4,8-Trimethoxy-3-(2-methallyl)-naphthalen-2-yl-methanol
(38). Compound 37 (100 mg, 0.30 mmol) in THF (3 mL) was added
drop wise to a stirred suspension of LAH (34.2 mg, 0.9 mmol) in THF
(5 mL) at rt. Reaction mixture was stirred at rt for 30 h. When the
reaction is complete, excess LAH was quenched with saturated
Na2SO4 solution. Then it was filtered through Celite pad. Residue
part was thoroughly washed with ethyl acetate. Crude product was
obtained after removal of solvent. Flash column chromatography
was done on silica gel with 1:1 EA/hexane to afford 38 (77.9 mg,
0.26 mmol) in 86% yield. Yellowish oil; Rf (1:1 EA/hexane) 0.45; 1H
J¼15.8 Hz, 1H), 7.58 (dd, J¼1.4, 7.8 Hz, 1H), 7.32 (dt, J¼1.4, 7.5 Hz,
1H), 7.27e7.22 (m, 1H), 7.21 (dd, J¼1.4, 7.6 Hz, 1H), 6.34 (d,
J¼15.8 Hz, 1H), 4.86e4.81 (m, 1H), 4.54 (dd, J¼1.1, 2.1 Hz, 1H), 4.26
(q, J¼7.1 Hz, 2H), 3.45 (s, 2H), 1.74 (t, J¼1.1 Hz, 3H), 1.33 (t, J¼7.1 Hz,
3H); 13C NMR (100 MHz, CDCl3)
d 167.2, 144.5, 142.6 (CH), 139.3,
134.0, 131.1 (CH), 130.1 (CH), 127.0 (CH), 126.7 (CH), 119.6 (CH), 112.8
(CH2), 60.7 (CH2), 41.8 (CH2), 22.9 (CH3), 14.5 (CH3); IR (KBr):
~
v¼2923, 2853, 1718, 1459, 1311, 1268, 1175, 1038, 979, 891, 768;
HRMS (ESI): m/z calculated for C15H18O2: requires: 231.1385 for
[MþH]þ, 157.1017 for [MꢂC3H4O2þH]þ; found: 231.1387, 157.1017.
NMR (400 MHz, CDCl3):
d
7.70 (d, J¼8.4 Hz, 1H), 7.42 (t, J¼8.4 Hz,
1H), 6.89 (d, J¼7.6 Hz,1H), 4.82 (d, J¼1.2 Hz,1H), 4.76 (s, 2H), 4.32 (s,
1H), 4.03 (s, 3H), 3.90 (s, 3H), 3.85 (s, 3H), 3.64 (s, 2H), 2.37 (bs, 1H),
3.4. 2-Isopropenylbenzaldehyde (41)13
1.91 (s, 3H); 13C NMR (100 MHz, CDCl3):
d 156.4, 152.1, 150.6, 146.5,
131.3, 131.0, 128.7, 126.7 (CH), 120.0, 115.4 (CH), 111.2 (CH2), 106.2
(CH), 63.4 (CH3), 62.3 (CH3), 58.2 (CH2), 56.3 (CH3), 34.5 (CH2), 23.8
Compound 41 was prepared following the literature procedure.
Only modification was quenching of last Grignard reaction with
saturated NH4Cl solution (5 mL/mmol). Colourless liquid; 1H NMR
~
(CH3); IR (KBr): v¼2919, 2848, 1638, 1566, 1443, 1220, 1069,
681 cmꢂ1; HRMS (ESI): m/z calculated for C18H22O4: requires:
(400 MHz, CDCl3)
(m, 1H), 7.33e7.25 (m, 2H), 5.34 (S, 1H), 4.83 (s, 1H), 2.09 (s, 3H); 13
NMR (50 MHz, CDCl3) 192.4 (CH), 147.8, 141.9, 133.6 (CH), 133.6,
d
10.13 (s, 1H), 7.84 (d, J¼7.6 Hz, 1H), 7.48e7.44
325.1416 for [MþNa]þ; found: 325.1417.
C
d
3.3.31. 1,4,8-Trimethoxy-3-(2-methallyl)-naphthalene-2-
carboxaldehyde (32). To a stirred solution of compound 38 (130 mg,
0.43 mmol) in 10 mL DCM was added PCC (185 mg, 0.86 mmol) at
0 ꢀC and stirred at rt for 3 h. Reaction mixture was passed through
basic alumina to remove PCC. Then flash column chromatography
was done on silica gel with 1:10 EA/hexane solvent to afford 32
(113.5 mg, 0.38 mmol) in 88% yield. Yellow liquid; Rf (1:10 EA/
128.7 (CH), 128.0 (CH), 127.6 (CH), 119.1 (CH2), 25.2 (CH3).
General procedures to perform the ene reactions:
3.4.1. With SnCl4$5H2O. A stirred solution of an O-propenyl arene
aldehyde (1 equiv) in dry solvent (10 mL/mmol) was stirred with
SnCl4$5H2O (50 mol%) in stoppered reaction flask. After completion
of the reaction, as monitored by TLC, it was quenched with satu-
rated solution of sodium bicarbonate (5 mL/mmol). Usual work-up
of the reaction mixture with EA or DCM furnished the mixture of
products. Products were purified by column chromatography on
basic alumina.
hexane) 0.35; 1H NMR (600 MHz, CDCl3)
d 10.62 (s, 1H), 7.72 (dd,
J¼1.0, 8.4 Hz, 1H), 7.59e7.53 (m, 1H), 6.94 (dd, J¼0.9, 7.8 Hz, 1H),
4.68e4.63 (m, 1H), 4.11 (m, 1H), 4.06 (s, 3H), 3.92 (s, 3H), 3.86 (d,
J¼0.8 Hz, 2H), 3.85 (s, 3H), 1.96e1.86 (m, 3H); 13C NMR (150 MHz,
CDCl3)
d 193.0, 160.5, 157.5, 151.0, 146.5, 134.3, 129.8 (CH), 128.6,
126.1, 119.5, 115.5 (CH), 109.5 (CH2), 106.8 (CH), 65.3 (CH3), 62.4
3.4.2. With BINOL-PO2H. A particular mol% of BINOL-PO2H was
added to a stirred solution of O-propenyl arene aldehyde (1 equiv)
in dry solvent (10 mL/mmol) in a stoppered reaction flask. Reaction
was monitored by TLC. After completion of reaction, it was slurried
with basic alumina and products were purified by column chro-
matography on basic alumina.
~
(CH3), 56.4 (CH3), 33.3 (CH2), 24.2 (CH3); IR (KBr): v¼2922, 2851,
1685, 1366, 1265, 1063, 913, 744 cmꢂ1; HRMS (ESI): m/z calculated
for C18H20O4: requires: 301.1440 for [MþH]þ; found: 301.1424.
3.3.32. Dimethyl 2-[2-(2-methallyl)-benzylidene]malonate (39).28
A
stirred solution of 10 (330 mg, 2.06 mmol), dimethyl malonate
(300 mg, 2.26 mmol), piperidine (0.02 mL, 0.206 mmol), and acetic
acid (0.012 mL, 0.206 mmol) in 10 mL benzene was heated at reflux
with a DeaneStark attachment for 9 h until no water was extracted.
The reaction mixture was diluted with EA and washed with HCl (5%
in water, 3ꢁ10 mL) and NaHCO3 (5% in water, 3ꢁ10 mL). The organic
layer was dried over Na2SO4, and the solvent was removed under
vacuum. Column chromatography of the residue with flash silica
gel and 2% EA in hexane afforded product 39 (395 mg, 1.44 mmol)
70% yield. Colourless oil; Rf (1:50 EA/hexane) 0.25; 1H NMR
3.4.3. With BINOL-PONHTf. A stirred solution of O-propenyl arene
aldehyde (1 equiv) in dry solvent (10 mL/mmol) was stirred with
a particular mol% of BINOL-PONHTf in a stoppered reaction flask. By
TLC reaction was monitored. After completion of reaction, it was
slurried with basic alumina and products were purified by column
chromatography.
3.4.4. 3-Methylene-1,2,3,4-tetrahydronaphthalen-1-ol (42) and 2-
methylnaphthalene (43). General procedure A was followed to
perform the ene-reaction on 10 (0.600 g, 3.75 mmol) with
SnCl4$5H2O (0.657 g, 1.87 mmol) in 37 mL dry EA at rt for 1.5 d.
Compound 43 (0.048 g, 0.34 mmol) was obtained as a white solid in
9% yield after column chromatography on basic alumina with
hexane. More polar product was eluted with 1:3 EA/n-hexane
solvent to give 42 (0.492 g, 3.08 mmol) as a white solid in 82% yield.
(400 MHz, CDCl3)
2H), 4.84 (s, 1H), 4.57 (s, 1H), 3.84 (s, 3H), 3.70 (s, 3H), 3.38 (s, 2H),
1.71 (s, 3H). 13C NMR (100 MHz, CDCl3)
167.0, 164.6, 143.9, 143.0
d 8.04 (s, 1H), 7.32e7.30 (m, 2H), 7.23e7.20 (m,
d
(CH), 139.3, 133.2, 130.8 (CH), 130.4 (CH), 128.1 (CH), 127.2, 126.8
(CH), 112.9 (CH2), 52.8 (CH3), 52.6 (CH3), 42.2 (CH2), 22.7 (CH3). IR
(KBr): v¼2923, 1735, 1612, 1435, 1261, 1219, 1068 cmꢂ1. HRMS (ESI):
~
m/z calculated for C16H18O4: requires: 297.1103 for [MþNa]þ,
275.1283 for [MþH]þ; found: 297.1100, 275.1264.
3.4.5. Data for 42. White solid; Rf (1:3 EA/hexane) 0.4; mp
43e45 ꢀC; 1H NMR (600 MHz, CDCl3)
d
7.42 (dd, J¼1.8, 7.3 Hz, 1H),
3.3.33. Ethyl 3-[2-(2-methallyl)phenyl]acrylate (40). To a stirred
solution of aldehyde 10 (280 mg, 1.75 mmol) in DCM (7 mL) was
added (carbethoxymethylene)triphenylphosphorane (822 mg,
2.4 mmol) at 0 ꢀC under inert atmosphere. This mixture was
allowed to warm to rt and stirred at the same temperature for 24 h.
The mixture was concentrated and slurried with silica gel. Column
7.26e7.19 (m, 2H), 7.13 (dd, J¼1.4, 7.4 Hz, 1H), 5.07 (t, J¼1.5 Hz, 1H),
5.00 (q, J¼1.4 Hz, 1H), 4.83 (dt, J¼4.6, 8.6 Hz, 1H), 3.57 (s, 2H), 2.73
(dd, J¼4.3, 13.2 Hz, 1H), 2.61 (dd, J¼4.8, 13.2 Hz, 1H), 1.89 (d,
J¼8.5 Hz, 1H); 13C NMR (150 MHz, CDCl3):
d 141.1, 138.6, 136.2, 129.1
(CH), 128.8 (CH), 128.2 (CH), 126.5 (CH), 112.3 (CH2), 69.8 (CH), 41.2
(CH2), 37.2 (CH2); IR (KBr): v¼3448, 2067, 1637, 673 cmꢂ1; HRMS
~

S. Basak, D. Mal / Tetrahedron 72 (2016) 1758e1772
1769
(ESI): m/z calculated for C11H12O: requires: 143.0861 for
[MꢂH2OþH]þ; found: 143.0832.
J¼7.6 Hz, 1H), 7.22 (d, J¼8.4 Hz, 1H), 5.57 (s, 1H), 5.14 (s, 1H), 5.09 (s,
1H), 3.69 (ABq, J¼18.8 Hz, 2H), 2.66 (ABq, J¼13.2 Hz, 2H), 1.92 (bs,
1H). 13C NMR (100 MHz, CDCl3):
d 140.7, 134.3, 132.7, 132.5, 132.5,
14
3.4.6. Data for 43. White solid; Rf (hexane) 0.55; mp 35e40 ꢀC;
128.9 (CH),128.7 (CH), 127.3 (CH),127.0 (CH),125.5 (CH),123.7 (CH),
1H NMR (200 MHz, CDCl3):
d
7.73e7.82 (m, 3H), 7.62 (s, 1H),
112.3 (CH2), 65.5 (CH), 41.0 (CH2), 38.3 (CH2). IR (KBr): v¼2922,
~
7.23e7.48 (m, 3H), 2.52 (s, 3H).
2065, 1634, 675 cmꢂ1. HRMS (ESI): m/z calculated for C15H14O: re-
quires: 193.1017 for [MꢂH2OþH]þ; found: 193.1011.
3.4.7. 3-Ethylidene-1,2,3,4-tetrahydronaphthalen-1-ol (47) and 2-
ethylnaphthalene (48). General procedure A was followed to per-
form ene-reaction of 11 (0.200 g, 1.15 mmol) with SnCl4$5H2O in
dry EA (6 mL) for 1.5 d. Two products formed. The less polar product
4815 (0.012 g, 0.08 mmol) was separated after column chroma-
tography on basic alumina with hexane in 7% yield. More polar
product 47 (0.172 g, 0.99 mmol) was eluted with 1:3 EA/hexane
solvent in 86% yield.
3.4.14. Data for 46.29 White solid; Rf (hexane) 0.55; mp 55e57 ꢀC.
1H NMR (400 MHz, CDCl3):
d
8.65 (d, J¼8.4 Hz, 1H), 8.58 (d,
J¼8.4 Hz, 1H), 7.87 (d, J¼8.4 Hz, 1H), 7.55e7.73 (m, 5H), 7.49 (d,
J¼8.4 Hz, 1H), 2.57 (s, 3H).
3.4.15. 7-Methoxy-3-methylene-1,2,3,4-tetrahydronaphthalen-1-ol
(52) and 2-methoxy-6-methylnaphthalene (44). General procedure
A was followed for the ICE of 12 (0.190 g, 1.00 mmol) with
SnCl4$5H2O (0.175 g, 0.50 mmol) at rt in 10 mL dry EA for 2 d.
Column chromatography on basic alumina afforded 52 (0.150 g,
0.78 mmol) in 78% yield and 44 (0.026 g, 0.15 mmol) in 15% yield.
3.4.8. Data for 47. Colourless liquid; Rf (1:3 EA/hexane) 0.45; 1H
NMR (400 MHz, CDCl3):
d 7.41e7.40 (m, 1H), 7.26e7.11 (m, 3H),
5.64e5.50 (m, 1H), 4.84e4.77 (m, 1H), 3.70e3.42 (m, 2H),
2.77e2.50 (m, 2H), 1.89 (bs, 1H), 1.71 (t, J¼5.0 Hz, 3H); 13C NMR
(100 MHz, CDCl3):
d
139.2,139.2,137.0,136.0,131.6,131.1,129.1 (CH),
3.4.16. Data for 52. Yellow oil; Rf (1:2 EA/hexane) 0.45; 1H NMR
128.8 (CH),128.3 (CH),128.1 (CH),128.1 (CH),128.0 (CH),126.3 (CH),
126.3 (CH), 121.6 (CH), 120.7 (CH), 69.8 (CH), 69.6 (CH), 42.2 (CH2),
38.8 (CH2), 34.9 (CH2), 31.2 (CH2), 13.3 (CH3), 13.1 (CH3); IR (KBr):
(600 MHz, CDCl3):
d
7.04 (d, J¼8.4 Hz, 1H), 6.96 (d, J¼2.4 Hz, 1H),
6.82 (dd, J¼2.4, 8.4 Hz, 1H), 5.05 (s, 1H), 4.98 (s, 1H), 4.78 (t,
J¼4.6 Hz, 1H), 3.80 (s, 3H), 3.5 (s, 2H), 2.72 (dd, J¼4.2, 13.0 Hz, 1H),
v¼3433, 2067, 1636, 673 cmꢂ1; HRMS (ESI): m/z calculated for
2.58 (dd, J¼5.0, 13.0 Hz, 1H); 13C NMR (100 MHz, CDCl3):
d 158.3,
~
C
12H14O: requires: 155.0861 for [MꢂH2OþH]þ, 173.0966 for
141.4, 139.7, 129.7 (CH), 128.1, 115.1 (CH), 113.1 (CH), 112.1 (CH2),
[MþH]þ; found: 155.0889, 173.0987.
70.0 (CH), 55.6 (CH3), 41.3 (CH2), 36.5 (CH2); IR (KBr): v¼3421, 2923,
~
2852, 1669, 1608, 1498, 1464, 1430, 1267, 1160, 1034, 878, 811 cmꢂ1
;
3.4.9. 3-Methylene-1,2,3,4-tetrahydrophenanthren-1-ol (49) and 3-
methylphenanthrene (51). General procedure A was adopted for
the ene-reaction of 15 (0.221 g, 1.05 mmol) with SnCl.45H2O
(0.184 g, 0.53 mmol) in dry EA (10 mL) at rt for 1.5 d. Column
chromatography on basic alumina with hexane afforded 51
(0.016 g, 0.084 mmol) 8% yield. More polar product 49 (0.188 g,
0.89 mmol) was obtained in 85% yield after eluting with 1:3 EA/
hexane solvent.
HRMS (ESI): m/z calculated for C12H14O: requires: 173.0966 for
[MꢂH2OþH]þ, 191.1072 for [MþH]þ; found: 173.0976, 191.1064.
3.4.17. Data for 44. 30Colourless liquid; Rf (hexane) 0.4; 1H NMR
(400 MHz, CDCl3):
1H), 7.13e7.11 (m, 2H), 3.91 (s, 3H), 2.48 (s, 3H); 13C NMR (50 MHz,
CDCl3): 157.2, 133.2, 132.9, 129.4, 128.9 (CH), 128.8 (CH), 126.9
d 7.67e7.64 (m, 2H), 7.55 (s, 1H), 7.30e7.27 (m,
d
(CH), 126.8 (CH), 118.8 (CH), 105.9 (CH), 55.5 (CH3), 21.7 (CH3).
3.4.10. Data for 49. White low melting solid; Rf (1:3 EA/hexane)
3.4.18. 5,8-Dimethoxy-3-methylene-1,2,3,4-tetrahydronaphthalen-1-
ol (53) and 1,4-dimethoxy-6-methylnaphthalene (45). General pro-
cedure B was followed for the ene-reaction of 13 (0.286 g,
1.30 mmol) with 10 mol% BINOL-PO2H (0.045 g, 0.13 mmol) in
CHCl3 (13 mL) at rt for 5 d. Two products were formed. Column
chromatography of the crude product on basic alumina with hex-
ane afforded aromatized product 45 (0.040 g, 0.20 mmol) in 15%
yield. More polar product 53 (0.229 g, 1.04 mmol) was obtained
upon eluting with 1:2 EA/hexane solvent in 80% yield.
0.35; mp 50e54 ꢀC; 1H NMR (400 MHz, CDCl3):
d
7.98 (d, J¼8.0 Hz,
1H), 7.84 (d, J¼8.0 Hz, 1H), 7.74 (d, J¼8.0 Hz, 1H), 7.57e7.49 (m, 3H),
5.20 (s, 1H), 5.10 (s, 1H), 4.96 (t, J¼4.2 Hz, 1H), 3.90 (ABq, J¼18.4 Hz,
2H), 2.83 (dd, J¼4.4, 12.8 Hz, 1H), 2.72 (dd, J¼4.4, 12.8 Hz, 1H), 1.92
(d, J¼9.2 Hz, 1H); 13C NMR (100 MHz, CDCl3):
d 141.04, 135.6, 133.4,
131.8, 131.7, 128.8 (CH), 127.3 (CH), 127.1 (CH), 126.5 (CH), 126.2
(CH), 123.5 (CH), 112.9 (CH2), 70.2 (CH), 41.2 (CH2), 34.6 (CH2); IR
(KBr): v¼3434, 2067, 1637, 672 cmꢂ1; HRMS (ESI): m/z calculated
~
for C15H14O: requires: 193.1017 for [MꢂH2OþH]þ, 211.1123 for
[MþH]þ; found: 193.1011, 211.1113.
3.4.19. Data for 53. Yellowish liquid; Rf (1:2 EA/hexane) 0.45; 1H
NMR (400 MHz, CDCl3):
d
6.71 (ABq, J¼8.8 Hz, 2H), 5.17 (t, J¼4.4 Hz,
3.4.11. Data for 51.29 White solid; Rf (hexane) 0.4; mp 62e64 ꢀC;1H
1H), 5.05 (s, 1H), 5.0 (s, 1H), 3.84 (s, 3H), 3.80 (s, 3H), 3.40 (ABq,
NMR (200 MHz, CDCl3):
J¼7.4 Hz, 1H), 7.79 (d, J¼7.8 Hz, 1H), 7.69 (s, 2H), 7.62 (d, J¼6.8 Hz,
1H), 7.59 (d, J¼6.2 Hz, 1H), 7.43 (d, J¼8.0 Hz, 1H), 2.63 (s, 3H).
d
8.68 (d, J¼7.4 Hz, 1H), 8.48 (s, 1H), 7.87 (d,
J¼19.2 Hz, 2H), 2.61 (m, 2H),1.62 (bs,1H); 13C NMR (100 MHz, CDCl3):
d 152.0, 151.2, 141.1, 128.2, 127.1, 111.9 (CH2), 109.3 (CH), 108.0 (CH),
64.7 (CH), 56.1 (CH3), 55.9 (CH3), 39.7 (CH2), 32.3 (CH2); IR (KBr):
v¼3439, 2063, 1636, 1219, 772 cmꢂ1; HRMS (ESI): m/z calculated for
~
3.4.12. 2-Methylene-1,2,3,4-tetrahydrophenanthren-4-ol (50) and 2-
methylphenanthrene (46). General procedure A was followed for
the ene-reaction on 16 (0.262 mmol, 1.25 mmol) with SnCl4$5H2O
(0.219 g, 0.63 mmol) in dry EA (12 mL) at rt for 1.5 d. Column
chromatography was done on basic alumina with hexane to afford
46 (0.01 g, 0.05 mmol) in 4% yield. Compound 50 (0.231 g,
1.10 mmol) was obtained after eluting with 1:3 EA/hexane solvent
in 88% yield.
C
13H16O3: requires: 243.0997 for [MþNa]þ; found: 243.0995.
3.4.20. Data for 45. 31Yellowish liquid; Rf (hexane) 0.55; 1H NMR
(400 MHz, CDCl3):
8.12 (d, J¼8.8 Hz, 1H), 8.01 (s, 1H), 7.35 (dd,
J¼2.0, 8.4 Hz, 1H), 6.66 (ABq, J¼8.2 Hz, 2H), 3.97 (s, 3H), 3.96 (s, 3H),
2.54 (s, 3H); 13C NMR (100 MHz, CDCl3):
149.8, 149.3, 135.8, 128.1
d
d
(CH), 126.7, 124.7, 121.9 (CH), 121.0 (CH), 103.5 (CH), 102.5 (CH), 55.9
(CH3), 55.9 (CH3), 22.1 (CH3).
3.4.13. Data for 50. White solid; Rf (1:3 EA/hexane) 0.4; mp
3.4.21. Compound 56 and 2,3-dimethoxy-6-methylnaphthalene
(54). General procedure C was followed for the ene-reaction of
14 (0.242 g, 1.10 mmol) with 1 mol% BINOL-PONHTf (0.005 g,
70e72 ꢀC; 1H NMR (400 MHz, CDCl3):
d
8.27 (d, J¼8.4 Hz, 1H), 7.81
(d, J¼8.4 Hz, 1H), 7.74 (d, J¼8.4 Hz, 1H), 7.57 (t, J¼7.6 Hz, 1H), 7.46 (t,

1770
S. Basak, D. Mal / Tetrahedron 72 (2016) 1758e1772
0.01 mmol) in CHCl3 (11 mL) at rt for 8 d. Two products were
formed. Column chromatography of crude products on basic alu-
mina with hexane afforded the aromatized product 54 (0.127 g,
0.63 mmol) in 57% yield. More polar product 56 (0.093 g,
0.44 mmol) was obtained upon eluting with 1:2 EA/hexane solvent
in 40% yield.
10 mol% BINOL-PO2H (0.028 g, 0.08 mmol) in CHCl3 (8 mL) at rt for
5 d. Exclusively 61 (0.198 g, 0.78 mmol) was obtained after column
chromatography on basic alumina with 1:3 EA/hexane solvent in
98% yield. Yellow solid; Rf (1:3 EA/hexane) 0.45; mp 137e138 ꢀC; 1H
NMR (600 MHz, CDCl3)
d
8.17 (d, J¼7.9 Hz, 1H), 8.04e8.00 (m, 1H),
7.96 (dd, J¼1.1, 7.7 Hz, 1H), 7.72 (t, J¼8.0 Hz, 1H), 7.57 (dd, J¼1.7,
7.9 Hz, 1H), 7.35 (dd, J¼1.0, 8.4 Hz, 1H), 4.05 (s, 3H), 2.51 (s, 3H); 13
C
3.4.22. Data for 56. Yellow liquid; Rf (1:2 EA/hexane) 0.35; 1H NMR
NMR (150 MHz, CDCl3) d 184.0, 182.8, 160.6, 144.5, 136.1, 135.4 (CH),
(400 MHz, CDCl3):
d
7.58 (d, J¼5.6 Hz, 1H), 7.47 (s, 1H), 7.23 (dd,
135.1 (CH), 133.1, 132.6, 127.7 (CH), 127.0 (CH), 121.8, 120.0 (CH),
~
J¼1.2, 5.6 Hz, 1H), 7.08 (s, 1H), 7.02 (s, 1H), 6.48 (s, 1H), 6.43 (s, 1H),
5.04 (t, J¼4.0 Hz, 1H), 3.98 (s, 3H), 3.83 (s, 3H), 3.64 (s, 3H),
3.22e3.20 (m, 2H), 2.60 (d, J¼10.0 Hz, 1H), 2.33 (d, J¼10.0 Hz, 1H),
118.2 (CH), 56.8 (CH3), 22.0 (CH3); IR (KBr): v¼2921, 2851, 1672,
1584, 1459, 1306, 1270, 1219 cmꢂ1; HRMS (ESI): m/z calculated for
C
16H13O3: requires: 253.0865 for [MþH]þ, 193.1017 for
1.35 (s, 3H), 1.13 (s, 3H); 13C NMR (100 MHz, CDCl3):
d
149.6, 149.2,
[MꢂCHO3þH]; found: 253.0852, 193.1011.
147.6, 147.1, 134.8, 129.3, 128.8, 127.9, 127.3 (CH), 127.2 (CH), 126.2,
125.9 (CH), 111.7 (CH), 108.3 (CH), 106.3 (2ꢁCH), 72.9 (CH), 71.3,
56.2 (CH3), 56.0 (CH3), 56.0 (CH3), 55.9 (CH3), 44.1 (CH2), 40.3 (CH2),
3.4.28. 1,9,10-Trimethoxy-6-methylanthracene (60). General pro-
cedure A was followed for the ene-reaction of 32 (0.270 g,
0.90 mmol) with SnCl4$5H2O (0.158 g, 0.50 mmol) in dry ethyl
acetate (9 mL). Column chromatography on basic alumina with
hexane afforded 60 (0.086 g, 0.31 mmol) in 34% yield. More polar
product 61 (0.141 g, 0.56 mmol) was obtained after eluting with 1:3
EA/hexane solvent in 62% yield.
ꢂ1
~
30.5 (CH3), 23.5 (CH3); IR (KBr): v¼2922, 1489, 1255, 1220 cm
;
HRMS (ESI): m/z calculated for C26H30O5: requires: 445.1991 for
[MþNa]þ, 405.2066 for [MþH]þ, 221.1178 for [MꢂC13H14O2þH]þ;
found: 445.1987, 405.2057, 221.1173.
32
3.4.23. Data for 54. White solid; Rf (hexane) 0.55; mp 55e57 ꢀC;
1H NMR (400 MHz, CDCl3):
d
7.59 (d, J¼8.2 Hz, 1H), 7.47 (s, 1H), 7.17
(dd, J¼1.6, 8.2 Hz, 1H), 7.09 (s, 1H), 7.05 (s, 1H), 3.99 (s, 6H), 2.47 (s,
3H), 2.47 (s, 3H); 13C NMR (50 MHz, CDCl3):
149.8, 149.1, 133.9,
3.4.29. Data for 60. Yellowish semisolid; Rf (1:3 EA/hexane) 0.5; 1H
NMR (600 MHz, CDCl3)
J¼8.4, 1H), 7.36e7.32 (m, 2H), 6.76 (d, J¼7.2 Hz, 1H), 4.07 (s, 6H),
4.01 (s, 3H), 2.51 (s, 3H); 13C NMR (150 MHz, CDCl3)
156.8, 149.4,
d
8.30 (d, J¼9.0 Hz, 1H), 7.99 (s, 1H), 7.87 (d,
d
129.6, 127.4, 126.5, 126.4 (CH), 125.8 (CH), 106.5 (CH), 106.1 (CH),
d
~
56.0 (2 OCH3), 21.7 (CH3); IR (KBr): v¼2964, 1608, 1511, 1493, 1455,
147.4, 135.9, 128.3 (CH), 127.5, 125.7, 125.3 (CH), 125.0, 123.5 (CH),
120.5 (CH), 117.8, 115.1 (CH), 103.5 (CH), 63.7 (CH3), 62.9 (CH3), 56.3
1414, 1256, 1206, 1161, 1127, 1013, 884, 855, 799, 749 cmꢂ1; HRMS
(ESI): m/z calculated for C13H14O2: requires: 203.1072 for [MþH]þ;
found: 203.1080.
~
(CH3), 22.4 (CH3); IR (KBr): v¼2932, 1685, 1555, 1450, 1266, 1215,
1066, 911, 678 cmꢂ1; HRMS (ESI): m/z calculated for C18H18O3: re-
quires: 253.0865 for [MꢂC2H6þH]þ; found: 253.0868.
3.4.24. Compound 57 and 1,2-dimethoxy-7-methylnaphthalene
(55). General procedure C was followed for the ene-reaction of
27 (0.220 g, 1.00 mmol) with 1 mol% BINOL-PONHTf (0.005 g,
0.01 mmol) in CHCl3 (10 mL) at rt for 7 d. Two products were
formed. Column chromatography was done by basic alumina with
hexane to afford the aromatized product 55 (0.115 g, 0.57 mmol) in
57% yield. Compound 57 (0.089 g, 0.42 mmol) was obtained in 42%
after eluting with 1:2 EA/hexane solvent.
3.4.30. Dimethyl 2-(3-methyl-1,2-dihydronaphthalen-1-yl)malonate
(65). General procedure C was followed for the ene-reaction of 39
(0.342 g, 1.25 mmol) with 20 mol% BINOL-PONHTf (0.120 g,
0.25 mmol) in toluene (12 mL) at 80 ꢀC for 80 h. Column chroma-
tography of the crude product on silica gel afforded compound 65
(0.322 g, 1.17 mmol) in 94% yield. Colourless oil; Rf (1:7 EA/hexane)
0.35; 1H NMR (400 MHz, CDCl3)
d 7.12e7.07 (m, 1H), 7.03e6.96 (m,
2H), 6.91 (d, J¼7.6, 1H), 6.19 (s, 1H), 3.67 (s, 3H), 3.65e3.59 (m, 1H),
3.4.25. Data for 57. Yellow liquid; Rf (1:2 EA/hexane) 0.4; 1H NMR
3.55e3.53 (m, 1H), 3.40 (s, 3H), 2.51e2.46 (m, 1H), 2.04e2.00 (m,
(600 MHz, CDCl3)
d
7.89e7.84 (m, 1H), 7.63 (d, J¼8.3 Hz, 1H), 7.54 (d,
1H), 1.80 (s, 3H); 13C NMR (100 MHz, CDCl3)
d 169.1, 168.9, 135.7,
J¼8.9 Hz, 1H), 7.26e7.23 (m, 1H), 7.21 (d, J¼8.9 Hz, 1H), 6.90 (d,
J¼8.4 Hz, 1H), 6.77 (d, J¼8.4 Hz, 1H), 5.11e5.03 (m, 1H), 3.98 (s, 3H),
3.92 (s, 3H), 3.84 (s, 3H), 3.69 (s, 3H), 3.35 (dd, J¼4.2,14.1 Hz,1H), 3.18
(dd, J¼6.6,14.1 Hz,1H), 2.68 (d, J¼16.0 Hz,1H), 2.37 (d, J¼16.0 Hz,1H),
134.7, 133.2, 128.2 (CH), 127.9 (CH), 126.3 (CH), 125.9 (CH), 122.8
(CH), 58.6 (CH), 52.7 (CH3), 52.4 (CH3), 38.4 (CH), 32.7 (CH2), 23.9
ꢂ1
~
(CH3); IR (KBr): v¼2927, 1736, 1437, 1261, 1220, 1152, 1023 cm
;
HRMS (ESI): m/z calculated for C16H18O4: requires: 297.1103 for
[MþNa]þ, 143.0861 for [M-dimethyl malonateþH]þ; found:
297.1115, 143.0878.
1.35 (s, 3H), 1.08 (s, 3H); 13C NMR (150 MHz, CDCl3)
d 150.9, 148.5,
146.3, 142.8, 137.0, 130.4, 129.0, 128.7, 128.6, 127.3 (CH), 127.1 (CH),
124.1 (CH), 121.7 (CH), 120.5 (CH), 114.4 (CH), 110.0 (CH), 72.3 (CH),
70.9, 61.3 (CH3), 60.4 (CH3), 57.1 (CH3), 55.9 (CH3), 44.0 (CH2), 34.5
General procedure A was also for the ene-reaction on 39 with
50 mol% SnCl4$5H2O in dry DCM. Column chromatography of the
crude products afforded product 65 and 43 in 49% and 42% yield
respectively.
~
(CH2), 30.7 (CH3), 23.8 (CH3); IR (KBr): v¼3442, 2920, 2850, 1633,
1462, 1276, 1219, 1066 cmꢂ1; HRMS (ESI): m/z calculated for
C
26H30O5: requires: 445.1991 for [MþNa]þ, 405.2066 for [MþH]þ,
221.1178 for [MꢂC13H14O2]þ; found: 445.1991, 405.2067, 221.1171.
3.4.31. Ethyl 3,3-dimethyl-3,4-dihydronaphthalene-2-carboxylate
(66) and 3,3-dimethyl-3,4-dihydronaphthalene-2-carboxylic acid
(67). General procedures A, B, C were followed for the ene-reaction
of 40 with SnCl4$5H2O, BINOL-PO2H, BINOL-PONHTf. Cyclization
didn’t occur at rt. Double bond of 40 isomerized in presence of
20 mol% rac-BINOL-phosphoramide in toluene at 100 ꢀC. After
dissolving the compound 40 (0.060 g, 0.26 mmol) in 3 mL dry DCM,
catalytic amount of BF.3OEt2 was added at 0 ꢀC under inert atmo-
sphere and the reaction mixture was allowed to warm and stirred
at rt for 48 h. Usual work-up procedure was done to get the crude
material. Flash column chromatography of the crude product on
silica gel with 1:5 EA/hexane solvent afforded the compounds 66
(0.020 g, 0.09 mmol) in 35% yield. More polar product 67 (0.030 g,
3.4.26. Data for 55. Yellowish liquid; Rf (hexane) 0.5; 1H NMR
(400 MHz, CDCl3):
d
7.88 (s, 1H), 7.67 (d, J¼8.4 Hz, 1H), 7.55 (d,
J¼8.4 Hz, 1H), 7.24e7.17 (m, 2H), 3.99 (s, 6H), 2.52 (s, 3H); 13C NMR
(100 MHz, CDCl3):
d 148.4, 135.8, 134.0, 129.1, 128.0, 127.5 (CH),
126.4 (CH), 123.9 (CH), 120.0 (CH), 114.1 (CH), 61.0 (CH3), 56.8 (CH3),
~
22.0 (CH3); IR (KBr): v¼2925, 2372, 1720, 1656, 1511, 1461, 1259,
1101, 771, 674 cmꢂ1. HRMS (ESI): m/z calculated for C13H14O2: re-
quires: 203.1072 for [MþH]þ; found: 203.1069.
3.4.27. 1-Methoxy-6-methylanthraquinone (61). General procedure
B was followed for the ene reaction of 32 (0.240 g, 0.80 mmol) with

S. Basak, D. Mal / Tetrahedron 72 (2016) 1758e1772
1771
0.15 mmol) was obtained after eluting with 1:1 EA/hexane solvent
in 57% yield. Formation of 67 was confirmed by transforming it into
its methyl ester.
added to a stirred solution of compound 42 (400 mg, 2.5 mmol) in
20 mL DCM at 0 ꢀC. After 5 min stirring at 0 ꢀC, TBDMSeCl
(452.2 mg, 3 mmol) was added. Reaction completed in 12 h. Usual
work up done with DCM to get the crude product. Flash column
chromatography was done on basic alumina with hexane to afford
pure silyl protected product 70 (560 mg, 2.3 mmol) in 93% yield.
Colourless liquid; Rf (hexane) 0.55; 1H NMR (600 MHz, CDCl3):
3.4.32. Data for 66. Yellowish liquid;Rf (1:5 EA/hexane) 0.4;1H NMR
(600 MHz, CDCl3)
(d, J¼7.4 Hz, 1H), 4.26 (q, J¼6.9 Hz, 2H), 2.74 (s, 2H), 1.36 (t, J¼7.0 Hz,
3H),1.25 (s, 6H); 13C NMR (150 MHz, CDCl3)
167.9, 138.7, 136.3, 135.1
d 7.28 (s, 1H), 7.24 (m, 1H), 7.22e7.16 (m, 2H), 7.13
d
d 7.47e7.40 (m, 1H), 7.25e7.17 (m, 2H), 7.13e7.06 (m, 1H), 4.97 (t,
(CH), 132.2, 129.5 (CH), 128.1 (CH), 127.9 (CH), 126.8 (CH), 60.4 (CH2),
J¼1.7 Hz, 1H), 4.92 (d, J¼1.6 Hz, 1H), 4.84 (dd, J¼5.0, 8.8 Hz, 1H),
3.63 (d, J¼18.4 Hz, 1H), 3.49 (d, J¼18.4 Hz, 1H), 2.73 (dd, J¼5.0,
13.2 Hz, 1H), 2.54e2.46 (m, 1H), 0.98 (s, 9H), 0.18 (s, 3H), 0.17 (s,
~
45.1 (CH2), 34.5, 26.1 (3ꢁCH3), 14.5 (CH3); IR (KBr): v¼2924, 2852,
1709,1458,1254,1217,1052, 717 cmꢂ1; HRMS (ESI): m/z calculated for
C
15H18O2: requires: 231.1385 for [MþH]þ; found: 231.1394.
3H); 13C NMR (150 MHz, CDCl3):
d 142.3, 140.4, 135.8, 128.1 (CH),
127.4 (CH), 126.7 (CH), 126.1 (CH), 110.5 (CH2), 70.8 (CH), 42.2
3.4.33. Data for 67. White solid; Rf (1:1 EA/hexane) 0.3; mp
146e148 ꢀC; 1H NMR (600 MHz, CDCl3)
7.52 (s, 1H), 7.28e7.26 (m,
1H), 7.23e7.22 (m, 2H), 7.16 (d, J¼6.8 Hz, 1H), 2.77 (s, 2H), 1.29 (s,
6H). 13C NMR (150 MHz, CDCl3)
173.3, 137.9 (CH), 137.2, 136.7,
(CH2), 37.1 (CH2), 26.1 (3ꢁCH3), 18.4, ꢂ4.0 (CH3), ꢂ4.4 (CH3); IR
~
d
(KBr): v¼3433, 2955, 2857, 2091, 1637, 1255, 1116, 1082, 887, 836,
774, 742; HRMS (ESI): m/z calculated for C17H26OSi: requires:
143.0861 [MeTBSOHþH]þ, 145.1017 for [MeTBSOHþ3H]þ,
146.1096 for [MeTBSOHþ4H]þ; found: 143.0855, 145.1005,
146.1046.
d
131.9,130.1 (CH),128.4 (CH),128.2 (CH),126.9 (CH), 45.2 (CH2), 34.4,
~
26.1 (2ꢁCH3). IR (KBr): v¼2959, 1672, 1413, 1270, 1220, 1033, 913.
HRMS (ESI): m/z calculated for C13H14O2: requires: 203.1072 for
[MþH]þ; found: 203.1054.
3.4.38. Tert-butyl-dimethyl-(3-methyl-1,2-dihydronaphthalen-1-
yloxy)silane (71).20 To a stirred solution of compound 70 (145 mg,
0.53 mmol) in a 5 mL dry ethanol were added 10 mol% Rh(PPh3)3Cl
(48.9 mg, 0.053 mmol) and DBU (0.79 mL, 5.3 mmol) under inert
atmosphere. Reaction was run for 10 days. Reaction mixture was
passed through basic alumina to separate catalyst. Column chro-
matography was done on basic alumina and eluted with only
hexane to get 71 (102 mg, 0.37 mmol) in 73% yield. Colourless
3.4.34. Methyl 3,3-dimethyl-3,4-dihydronaphthalene-2-
carboxylate. Yellowish liquid; Rf (1:5 EA/hexane) 0.45; 1H NMR
(600 MHz, CDCl3)
2H), 7.15e7.12 (m, 1H), 3.80 (s, 3H), 2.74 (s, 2H), 1.24 (s, 6H); 13C
NMR (150 MHz, CDCl3) 168.2, 138.3, 136.4, 135.5 (CH), 132.1, 129.6
d 7.29 (s, 1H), 7.26e7.22 (m, 1H), 7.22e7.16 (m,
d
(CH), 128.1 (CH), 128.0 (CH), 126.8 (CH), 51.6 (CH3), 45.1 (CH2), 34.5,
26.1 (2ꢁCH3); IR (KBr): v¼2925, 1710, 1445, 1256, 1219, 1052; HRMS
liquid; Rf (hexane) 0.55; 1H NMR (600 MHz, CDCl3)
d 7.38 (q,
J¼4.7 Hz, 1H), 7.16 (m, 2H), 6.97 (dd, J¼3.3, 5.9 Hz, 1H), 6.20 (d,
J¼4.6 Hz, 1H), 4.93 (m, 1H), 2.39 (t, J¼13.9 Hz, 1H), 2.29 (dd, J¼6.4,
16.3 Hz, 1H), 1.92 (s, 2H), 0.96 (s, 9H), 0.13 (s, 3H), 0.12 (s, 3H); 13C
NMR (150 MHz, CDCl3) d 137.2, 136.0, 134.4, 127.4 (CH), 126.6 (CH),
125.3 (CH), 124.7 (CH), 122.8 (CH), 69.8 (CH), 39.2 (CH2), 26.1
~
(ESI): m/z calculated for C14H16O2: requires: 217.1229 for [MþH]þ;
found: 217.1243.
3.4.35. 3-Methyl-1H-inden-1-ol (68).19 General procedure C was
performed on 41 (0.219 g, 1.50 mmol) with 10 mol% BINOL-PONHTf
(0.072 g, 0.15 mmol) in dry toluene (15 mL) at rt for 12 h. Product 68
(0.210 g, 1.44 mmol) was found in 96% yield. Yellow oil; Rf (1:2 EA/
~
(3ꢁCH3), 23.7, 18.5, ꢂ4.6 (CH3), ꢂ4.3 (CH3); IR (KBr): v¼3448, 2955,
2929, 2857, 1459, 1255, 1220, 1111, 1078, 836, 812, 676, 474 cmꢂ1
;
hexane) 0.4; 1H NMR (400 MHz, CDCl3):
d
7.47 (d, J¼7.6 Hz, 1H),
HRMS (ESI): m/z calculated for C17H26OSi: requires: 145.1017 for
[MeTBSOHþ3H]þ, 146.1096 for [MeTBSOHþ4H]þ; found:
145.1005, 146.1070.
7.29e7.33 (m, 1H), 7.19e7.24 (m, 2H), 6.04 (d, J¼1.6 Hz, 1H), 5.08 (s,
1H), 2.21 (bs, 1H), 2.09 (t, J¼1.6 Hz, 3H); 13C NMR (50 MHz, CDCl3):
d
146.3, 144.0, 141.5, 132.6 (CH), 128.4 (CH), 126.2 (CH), 123.3 (CH),
~
119.3 (CH), 76.4 (CH), 13.0 (CH3). IR (KBr): v¼3354, 2928, 1615, 1410,
1220, 1077, 1044 cmꢂ1. HRMS (ESI): m/z calculated for C10H10O:
requires: 129.0704 for [MꢂH2OþH]þ, 145.0653 for [Mꢂ2HþH]þ;
found: 129.0692, 145.0643.
3.4.39. Tert-butyl-dimethyl-(1a-methyl-1a,2,3,7b-tetrahydro-1-oxa-
cyclopropa[a]naphthalen-3-yloxy)silane (72).21 To a stirred solution
of 71 (100 mg, 0.36 mmol) in 4 mL acetone were added 0.8 mL EA,
0.8 mL water and solid NaHCO3 (91.7 mg, 2.16 mmol) and the re-
action mixture was stirred for 10 min. To this was added solid oxone
(448.6 mg, 0.728 mmol) and contents were stirred at room tem-
perature for 45 min. After completion of the reaction, the excess
acetone evaporated under vacuum and remaining reaction mixture
was portioned between water and EA (20 mL each). The organic
layer was separated and the aqueous layer extracted with EA
(2ꢁ20 mL). Combined organic layer was dried (Na2SO4) and con-
centrated under reduced pressure. Column chromatography of the
crude product was done on silica gel with hexane to afford the
corresponding epoxide 72 (73.1 mg, 0.252 mmol) in 69% yield.
3.4.36. 3-Methylene-1,2,3,4-tetrahydronaphthalen-1-ylacetate
(69). To a stirred solution of 42 (100 mg, 0.6 mmol) in Ac2O (0.3 mL,
3.12 mmol) was added pyridine (0.29 mL, 3.43 mmol). It was stirred
for 18 h. Then reaction mixture was diluted with EA (30 mL) and
successively washed with CuSO4 solution (3ꢁ10 mL) to remove
pyridine. Organic layers was washed with brine (10 mL) and dried
over Na2SO4. Solvent was evaporated to get crude product. Flash
column chromatography was done on silica gel with 1:10 EA/hex-
ane to afford pure product 69 (61 mg, 0.3 mmol) in 50% yield. Yellow
liquid; Rf (1:10 EA/hexane) 0.35; 1H NMR (400 MHz, CDCl3):
Colourless liquid; Rf (hexane) 0.45; 1H NMR (600 MHz, CDCl3)
d 7.52
d
7.31e7.25 (m, 2H), 7.22e7.14 (m, 2H), 6.02 (t, J¼4.8 Hz,1H), 5.02 (s,
1H), 4.95 (s, 1H), 3.61 (ABq, J¼18.4, 2H), 2.70 (d, ABq, J¼4.8, 14.0 Hz,
2H), 2.07 (s, 3H); 13C NMR (100 MHz, CDCl3):
170.9, 140.4, 137.2,
(td, J¼1.0, 7.2 Hz, 1H), 7.37 (dt, J¼1.3, 7.4 Hz, 2H), 7.24 (td, J¼1.0,
7.4 Hz, 1H), 4.86 (tdd, J¼1.0, 6.4, 10.7 Hz, 1H), 3.67 (s, 1H), 2.47 (dd,
J¼6.5, 13.8 Hz, 1H), 1.79 (dd, J¼10.9, 13.8 Hz, 1H), 0.99 (s, 9H), 0.17 (s,
d
134.5,129.2 (CH),128.8 (CH),128.7 (CH),126.4 (CH),111.8 (CH2), 71.6
(CH), 37.7 (CH2), 36.8 (CH2), 21.6 (CH3); HRMS (ESI): m/z calculated
for C13H14O2: requires: 222.0895 for [MꢂCH3CHOþCH3CNþNa]þ;
found: 222.0866.
3H), 0.16 (s, 3H); 13C NMR (150 MHz, CDCl3)
d 140.6, 132.3, 129.0
(CH), 128.9 (CH), 126.9 (CH), 124.7 (CH), 66.6 (CH), 60.7 (CH), 59.0,
37.6 (CH2), 26.1 (3ꢁCH3), 21.9 (CH3), 18.4, ꢂ4.3 (CH3), ꢂ4.7 (CH3); IR
ꢂ1
~
(KBr): v¼2925, 2853, 1461, 1253, 1220, 1121, 1092, 873, 839 cm
;
HRMS (ESI): m/z calculated for C17H26O2Si: requires: 131.0861 for
[MeTBSOHeHCHOþH]þ, 159.0801 for [MeTBSOHþH]þ, 299.1436
for [2Mꢂ2TBSOHeH2OþH]þ, 431.2406 for [2MeTBSOHeH2OþH]þ,
3.4.37. Tert-butyl-dimethyl-(3-methylene-1,2,3,4-tetrahydronaph
thalen-1-yloxy)silane (70). Imidazole (850.9 mg, 12.5 mmol) was

1772
S. Basak, D. Mal / Tetrahedron 72 (2016) 1758e1772
563.3377 for [MþMeH2OþH]þ; found: 131.0860, 159.0810,
Vicente, F.; Basilio, A.; Bills, G. F.; Donald, R. G. K.; Phillips, J. W.; Goetz, M. A.;
Singh, S. B. J. Nat. Prod. 2014, 77, 497e502; (c) Beattiea, K. D.; Roufa, R.; Gandera,
L.; Mayb, T. W.; Ratkowskyc, D.; Donner, C. D.; Gill, M.; Grice, D.; Tiralongo, E.
Phytochemistry 2010, 71, 948e955; (d) Elsworth, C.; Gill, M.; Saubern, S. Phy-
tochemistry 2000, 55, 23e27; (e) Muangsina, N.; Wisetsakdakorna, W.; Chai-
chitb, N.; Sihanonthc, P.; Petsom, A.; Sangvanich, P. Dyes Pigments 2008, 77,
653e656; (f) Apsel, B.; Bender, J. A.; Escobar, M.; Kaelin, D. E.; Lopez, O. D.;
Martin, S. F. Tetrahedron Lett. 2003, 44, 1075e1077; (g) Kim, M. C.; Hwang, E.;
Kim, T.; Ham, J.; Kim, S. Y.; Kwon, H. C. J. Nat. Prod. 2014, 77, 2326e2330; (h)
Kuntsmann, M. A.; Mitscher, L. A. J. Org. Chem. 1966, 31, 2920e2925; (i) Khalil,
Z. G.; Raju, R.; Piggott, A. M.; Salim, A. A.; Blumenthal, A.; Capon, R. J. J. Nat. Prod.
2015, 78, 949e952; (j) Achmatowicz, O.; Szechne, B. J. Org. Chem. 2003, 68,
2398e2404; (h) Sezaki, M.; Hara, T.; Ayukawa, S.; Takeuchi, T.; Okami, Y.;
Hamada, M.; Nagatsu, T.; Umezawa, H. J. Antibiot. 1968, 11, 91e97.
299.1445, 431.2404, 563.3361.
3.4.40. 3-Methylnaphthalen-1-ol (73).33 To a stirred solution of
compound 42 (100 mg, 0.63 mmol) in dry DCM was added PDC
(406 mg, 1.89 mmol) and stirred for 5 h until the starting material
vanished. After completion of the reaction, reaction mixture was
directly passed through basic alumina and eluted with 1:5 EA/
hexane to afford oxidized product 73 (84 mg, 0.53 mmol) in 83%
yield. Yellowish solid; Rf (1:5 EA/hexane) 0.4; 1H NMR (400 MHz,
CDCl3):
2H), 7.25 (s, 1H), 6.7 (s, 1H), 2.47 (s, 3H); 13C NMR (50 MHz, CDCl3):
151.1, 135.8, 134.9, 127.0 (CH), 126.5 (CH), 124.3 (CH), 122.6, 121.3
d
8.13 (d, J¼8.0 Hz, 1H), 7.74 (d, J¼8.0 Hz, 1H), 7.42e7.50 (m,
8. Ghorai, S. K.; De, S. R.; Karmakar, R.; Hazra, N. K.; Mal, D. Res. Lett. Org. Chem.
2009 Article ID 528081, 5 pages.
d
ꢀ ꢀ
9. (a) Tabele, C.; Curti, C.; Primas, N.; Karbi, Y.; Remusat, V.; Vanelle, P. Synthesis
2015, 47, 3339e3346; (b) Jagdale, A. R.; Park, J. H.; Youn, S. W. J. Org. Chem. 2011,
76, 7204e7215; (c) In coupling reactions, side products originating from ho-
mocoupling of the boronic acids were also obtained, albeit in smaller amounts.
(d) Rondla, N. R.; Ogilvie, J. M.; Pan, Z.; Douglas, C. J. Chem. Commun. 2014,
8974e8977; (e) Xing, S.; Pan, W.; Liu, C.; Ren, J.; Wa, Z. Angew. Chem., Int. Ed.
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ybiphenyl-2, 20-carboxaldehyde was also obtained in 10% yield; (h) Takada, T.;
Arisawa, M.; Gyoten, M.; Hamada, R.; Tohma, H.; Kita, Y. J. Org. Chem. 1998, 63,
7698e7706.
(CH), 119.7 (CH), 110.8 (CH), 21.7 (CH3).
3.4.41. 2-Methyl-1,4-naphthoquinone (74).34 To a stirred solution of
compound 42 (100 mg, 0.63 mmol) in dry DCM (6 mL) was added
PCC (406.4 mg, 1.89 mmol) and stirred for 5 h until the starting
material vanished. After completion of the reaction, the mixture
was directly passed through basic alumina and eluted with 1:5 EA/
hexane solvent to furnish over-oxidized product 74 (81%). Red
solid; Rf (1:5 EA/hexane) 0.35; 1H NMR (400 MHz, CDCl3):
10. (a) Koepf, M.; Melin, F.; Jaillard, J.; Weiss, J. Tetrahedron Lett. 2005, 46, 139e142;
(b) Speicher, A.; Groh, M.; Hennrich, M.; Huynh, A. M. Eur. J. Org. Chem. 2010,
6760e6778; (c) Geen, G. R.; Mann, I. S.; Mullane, M. V. Tetrahedron 1998, 54,
9875e9894.
11. Koning, C. B. D.; Michael, J. P.; Rousseau, A. L. J. Chem. Soc.,Perkin Trans. 1 2000,
787e797.
12. (a) Fan, E.; Shi, W.; Lowary, T. D. J. Org. Chem. 2007, 72, 2917e2928; (b) Mal, D.;
Ray, S.; Sharma, I. J. Org. Chem. 2007, 72, 4981e4984; (c) Mal, D.; Pahari, P.
Chem. Rev. 2007, 107, 1892e1918; (d) Donner, C. D. Tetrahedron 2013, 69,
3747e3773; (e) Freskos, J. N.; Morrow, G. W.; Swenton, J. S. J. Org. Chem. 1985,
50, 805e810.
d
8.05e8.12 (m, 2H), 7.72e7.75 (m, 2H), 6.85 (d, J¼1.2 Hz, 1H), 2.20
(d, J¼1.2 Hz, 3H); 13C NMR (100 MHz, CDCl3):
d 185.8, 185.2, 148.4,
135.9 (CH), 133.9 (CH), 133.8 (CH), 132.5, 132.4, 126.8 (CH), 126.3
(CH), 16.7 (CH3).
Acknowledgements
13. Hatano, B.; Miyoshi, K.; Sato, H.; Ito, T.; Ogata, T.; Kijima, T. Tetrahedron Lett.
We gratefully acknowledge the Council of Scientific and
Industrial Research (CSIR) for financial support (02(0183)/14/EMR-
II), and the Department of Science and Technology for in-
strumental facilities. S. B. thanks CSIR for his research fellowship
(09/081(1177)/2012-EMR-I).
2010, 51, 5399e5401.
14. Chen, Y. Z.; Ni, C. W.; Teng, F. L.; Ding, Y. S.; Lee, T. H.; Ho, J. H. Tetrahedron 2014,
70, 1748e1762.
15. Brunel, J. M. Tetrahedron 2007, 63, 3899e3906.
16. Thomson, R. H. Naturally Occurring Quinones IVdRecent Advances; Blackie Ac-
ademic & ProfesionaldAn imprint of Chapman & Hall, 1997.
17. (a) Parmar, D.; Sugiono, E.; Raja, S.; Rueping, M. Chem. Rev. 2014, 114,
9047e9153; (b) Rueping, M.; Theissmann, T.; Kuenkel, A.; Koenigs, R. M. Angew.
Chem., Int. Ed. 2008, 47, 6798e6801; (c) Rueping, M.; Bootwicha, T.; Kambutong,
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Liu, L.; Leutzsch, M.; Zheng, Y.; Alachraf, M. W.; Thiel, W.; List, B. J. Am. Chem.
Soc. 2015, 137, 13268e13271.
Supplementary data
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.tet.2016.02.033.
18. (a) Dethe, D. H.; Murhade, G. M. Chem. Commun. 2013, 8051e8053; (b) Mal, D.;
Jana, A.; Ray, S.; Bhattacharya, S.; Patra, A.; De, S. Synth. Commun. 2008, 38,
3937e3946.
19. Inci, B.; Cheng, P. N.; Beljanski, K.; Moore, J. S. ACS Macro Lett. 2013, 2, 935e938.
20. Schmidt, B. J. Org. Chem. 2004, 69, 7672e7687.
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