Triflic acid catalysed regioselective synthesis of substituted naphthalenes by benzannulation of carbonyls with alkynes

Article abstract of DOI:10.1016/j.tet.2021.132214

An interesting and facile triflic acid catalysed annulation of α-aryl carbonyls with arylalkynes is presented for the regioselective synthesis of substituted naphthalenes. The annulation reaction involves a sequence of electrophilic attack of carbonyl on arylalkyne and benzannulation catalysed by triflic acid. The present catalyst effects this transformation at room temperature itself. Intramolecular version of the present Br?nsted acid catalysis furnished compounds containing 1-arylnaphthalene core fused with ring systems in excellent yields.

Full text of DOI:10.1016/j.tet.2021.132214

Tetrahedron xxx (xxxx) xxx
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Triflic acid catalysed regioselective synthesis of substituted
naphthalenes by benzannulation of carbonyls with alkynes
Vanajakshi Gudla*, Mokhamatam Sudheer, Chinthu Joginarayana Rao,
Paul Douglas Sanasi, Venkateswara Rao Battula 1
Department of Engineering Chemistry, AUCE (A), Andhra University, Visakhapatnam, 530003, India
a r t i c l e i n f o
a b s t r a c t
Article history:
An interesting and facile triflic acid catalysed annulation of
a-aryl carbonyls with arylalkynes is pre-
Received 25 March 2021
Received in revised form
26 April 2021
Accepted 1 May 2021
Available online xxx
sented for the regioselective synthesis of substituted naphthalenes. The annulation reaction involves a
sequence of electrophilic attack of carbonyl on arylalkyne and benzannulation catalysed by triflic acid.
The present catalyst effects this transformation at room temperature itself. Intramolecular version of the
present Brønsted acid catalysis furnished compounds containing 1-arylnaphthalene core fused with ring
systems in excellent yields.
© 2021 Elsevier Ltd. All rights reserved.
Keywords:
Arylnaphthalene
Triflic acid
Benzannulation
a
-Aryl carbonyls
Alkynes
1. Introduction
synthetic chemists for making the collection of 1-arylnaphthelenes
to screen them for their activities. So, efforts have been made to
The identification and development of synthetic routes for the
biologically active molecules gained lot of interest due to their
significant contribution as sources for new drugs [1]. Particularly
the synthesis of naphthalene derivatives has occupied special place
in the field of organic synthesis and medicinal chemistry as naph-
thalene core is presented in numerous biologically active com-
pounds and important natural products [2]. Apart from the
biological importance, compounds containing naphthalene skel-
eton find applications as optical and electronic materials [3]. Hence,
there has been special interest in developing efficient strategies for
making naphthalene core. Among naphthalene derivatives, espe-
cially 1-arylnaphthelenes are important because they are presented
in several naturally occurring lignan lactones which gained lot of
attention due to their wide range of biological activities [4] such as
5-lipoxygenase inhibition [5], phosphodiesterase inhibition [6],
antiviral [7], antitumor [8], and antibacterial properties [9], cyto-
toxicity [10] and HIV reverse transcriptase inhibition [11]. In this
context, there has been considerable attention and interest among
develop strategies for the synthesis of 1-arylnaphthalenes [12].
Among the different developed strategies so far, annulation of al-
kynes and arylmethyl carbonyls is one of the well-established and
efficient methods [13,14]. To the best of our knowledge, until now
there are several metal catalysed/mediated (Ga [13a], Ti [13b], Au
[13c,d], Fe [13e], Ru [13g]) and BF3$Et2O [13f] catalysed reactions
studied for this type of annulation reaction. It is an important
observation that these all are based on Lewis acid catalysed/
mediated reactions. But if we look into Brønsted acid catalysed/
mediated naphthalene annulation from alkyne and arylmethyl
carbonyls, to the best of our knowledge there is only one report on
Brønsted acid catalysed/mediated annulation for the synthesis of 1-
arylnaphthalene core which is an HNTf2 (triflimide) catalysed re-
action [14]. The growing synthetic importance of naphthalene de-
rivatives especially in regioselective manner demands alternative
methods to access them under mild reaction conditions. In this
context, herein we describe triflic acid (TfOH or CF3SO3H) catalysed
annulation reactions of arylmethyl carbonyls and arylalkynes for
the synthesis of 1-arylnaphthalenes in both inter- and intra-
molecular versions. This metal free and Brønsted acid catalysed
reaction smoothly works at room temperature under mild condi-
tions for providing broad range of substituted 1-arylnaphthalenes.
During the study of the role of possible Brønsted acid that could
* Corresponding author.
E-mail address: gayathri.vanaja@gmail.com (V. Gudla).
mentor.
1
https://doi.org/10.1016/j.tet.2021.132214
0040-4020/© 2021 Elsevier Ltd. All rights reserved.
Please cite this article as: V. Gudla, M. Sudheer, C.J. Rao et al., Triflic acid catalysed regioselective synthesis of substituted naphthalenes by
benzannulation of carbonyls with alkynes, Tetrahedron, https://doi.org/10.1016/j.tet.2021.132214

V. Gudla, M. Sudheer, C.J. Rao et al.
Tetrahedron xxx (xxxx) xxx
form under the reaction conditions of gold-catalysed annulation of
arylmethyl carbonyls and arylalkynes [13d], it was observed that
catalytic amount of triflic acid can promote the annulation for
naphthalene formation. Though the yields were very less, it gave a
hope that the reaction conditions can be optimized for improve-
ment of yields under triflic acid catalysis. And as mentioned earlier,
to the best of our knowledge, there is only one Brønsted acid known
in the literature for naphthalene formation from annulation of
arylmethyl carbonyls and arylalkynes [14]. Considering these as-
pects, we were curious to develop triflic acid catalysed cyclisation
reaction of arylmethyl carbonyls and arylalkynes for the regiose-
lective synthesis of 1-arylnaphthalenes. After achieving the target,
the reaction was studied in intramolecular fashion to obtain aryl-
naphthalenes fused with ring systems, some of which can act as
scaffolds for arylnaphthalene lignan lactones.
there is only slight difference in the reaction yield between reaction
with 20 mol% and 30 mol%. Hence, we decided to carry out further
optimization with 20 mol% catalyst only. When reaction was per-
formed in refluxing dichloromethane, after 6 h of reaction, starting
materials started decomposing (entry 6). To find out suitable sol-
vent for the present annulation reaction, different solvents were
tested (vide infra). Reaction in dichloroethane (DCE) led to consid-
erable increase in the formation of 3a by forming 59% (entry 7).
Soon after reaction was performed in DCE at reflux temperature
which led to decomposition of starting materials after 6 h (entry 8)
as in the case of reaction in refluxing dichloromethane. Thus,
remaining all optimization reactions were carried out at RT only.
When methanol and tetrahydrofuran (THF) were being used as
solvent, formation of complex mixture of products was observed
(entries 9 and 10). When the reaction was carried out in acetonitrile
solvent, to our delight, yield of 3a was increased drastically to 71%
(entry 11). Later reaction was conducted in acetonitrile solvent by
increasing amount of phenylacetylene 2a from 1.2 equiv. to 2.0
equiv. which did not improve the yield much (73%) (entry 12).
Hence, the remaining optimization reactions and study of substrate
scope were carried out using 1.0 equiv. of arylacetaldehydes and 1.2
equiv. of arylalkynes. Though the cyclisation took place in 1,4-
dioxane and nitromethane solvents, yields are lesser and reaction
times are longer relatively. Hence, the optimum reaction conditions
for the annulation of arylmethyl carbonyls and arylalkynes to give
1-arylnaphthalenes are: 1.0 equiv. of 1, 1.2 equiv. of 2, TfOH (20 mol
%) and acetonitrile as solvent at room temperature (Table 1, entry
11).
2. Results and discussion
2.1. Triflic acid catalysed annulation approach to synthesize 1-
arylnaphthalenes
We carried out several experiments by taking commercially
available simple phenylacetaldehyde 1a and phenylacetylene 2a to
find out the optimum reaction conditions for triflic acid catalysed
1-arylnaphthalene synthesis (Table 1). Initially, we started the re-
action using 1.0 equiv. of 1a and 1.2 equiv. of 2a in dry dichloro-
methane solvent at room temperature (RT) with 2 mol% of triflic
acid (TfOH). The reaction resulted in 9% of 1-phenylnaphthalene 3a
(Table 1, entry 1). Though the reaction was allowed to stir for 24 h,
there was no progress in the reaction after 6 h. Later, catalyst
loading was increased in the reaction to 5 mol%, 10 mol%, 20 mol%
and 30 mol% which resulted in improvement in the yield and
decrease in the reaction time (entries 2e5). It was observed that
2.2. Scope of triflic acid catalyst in 1-arylnaphthalene synthesis
The scope of triflic acid catalyst in the synthesis of substituted 1-
arylnaphthalenes was examined by employing diverse substituted
a
-aryl aldehydes/ketones and arylalkynes under optimized reac-
tion conditions. Table 2 summarises the outcome of these reactions.
The regioselectivity was exceptional as only the 1-arylnaphthalene
derivatives 3 were obtained. The reactions studied were reasonably
fast and completed in 4e7 h. Triflimide (HNTf2) catalysed ben-
zannulation reaction for naphthalene synthesis took relatively
much more reaction times i.e., 13e48 h [14]. This shows the su-
periority of triflic acid catalyst over triflimide catalyst. Initially re-
Table 1
Screening of reaction conditions in the annulation of phenylacetaldehyde 1a and
phenylacetylene 2aa.
actions
phenylacetaldehydes with arylalkynes were tested (entries 1e14
and 19e22). Phenylacetaldehyde having -substituents (1b, 1c and
of
phenylacetaldehyde
and
substituted
a
1d) could be used which resulted in 1,4-substituted naphthalenes
(entries 4e8 and 19) smoothly. Arylmethyl aldehydes with both
electron withdrawing groups such as Cl, F and donating groups
such as alkoxy (eOeCH2eOe) groups were found to yield their
corresponding 1-arylnaphthalene derivatives. As well as ary-
lalkynes with both electron withdrawing groups such as Cl, F and
donating groups such as alkyl and alkoxy groups were used for this
annulation study. Both terminal (entries 1, 5, 8, 11, 13, 15 and 16)
and internal arylalkynes (entries 2e4, 6, 7, 9, 10, 12, 14 and 17e20)
were employed in this study and found that both types participated
in the annulation. This observation makes triflic acid very special
catalyst for this type of annulation as internal alkynes did not un-
dergo cyclisation under BF3$Et2O catalysis [13f] and terminal al-
kynes did not participate in FeCl3-promoted annulation reaction
[13e]. Bromo-substituted naphthalene could be obtained in good
yield using this methodology (entry 2), and other halogens chloro
and fluoro substituted naphthalene derivatives could also be made
(entries 9e13) which can be utilized for further transformations
such as metal catalysed coupling reactions (for example palladium
catalysed Sonogashira, Heck, Stille, Negishi and Suzuki-Miyaura etc.
cross-couplings) to make polyfunctionalised naphthalene
Entry
Catalyst (mol%)
Solvent and condition
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
2
5
CH2Cl2, RT
CH2Cl2, RT
CH2Cl2, RT
CH2Cl2, RT
CH2Cl2, RT
CH2Cl2, reflux
DCE, RT
DCE, reflux
MeOH, RT
THF, RT
24c
24c
24c
9
9
15
21
43
44
39
59
10
20
30
20
20
20
20
20
20
20
20
20
9
6d
8
6d
5
48
__e
9
__e
10
11
12
13
14
5
5
5
10
10
CH3CN, RT
CH3CN, RT
CH3NO2, RT
1,4-dioxane, RT
71
73f
42
49
a
All reactions were carried out with phenylacetaldehyde 1a (1.0 equiv.) and
phenylacetylene 2a (1.2 equiv.) unless otherwise stated.
b
Isolated yield.
After 6 h, there was no progress in the reaction.
After 6 h, reactants started decomposing.
Complex mixtures of products.
c
d
e
f
Reaction was carried out using phenylacetaldehyde 1a (1.0 equiv.) and phe-
nylacetylene 2a (2.0 equiv.).
2

Table 2
Scope of triflic acid catalyst in 1-arylnaphthalene synthesis.a
3

V. Gudla, M. Sudheer, C.J. Rao et al.
Tetrahedron xxx (xxxx) xxx
(continued on next page)
4

V. Gudla, M. Sudheer, C.J. Rao et al.
Tetrahedron xxx (xxxx) xxx
Table 2 (continued)
derivatives. 1-Arylnaphthalene having chloro functionality at
multiple places could also be achieved (entry 11). Naphthalene
derivatives having an alkyl bromide side chain (3l) could also be
made using the present method (entry 12) which can be utilized as
alkylating reagents. The present annulation method was then
reaction mechanism (Scheme 1). Initially, carbonyl oxygen atom of
1 is protonated which enhances the electrophilicity of carbonyl
carbon (formation of cation A). Electrophilic attack of the carbonyl
carbon of A on the arylalkyne 2 takes place to form a new CeC bond
at the b-carbon of the arylalkyne 2 as the resulting vinyl carboca-
further extended by employing
a
-arylmethyl ketones (entries
tion (B) is stabilized by the aryl group (Ar). Intramolecular aromatic
electrophilic substitution reaction happens in B to form the bicyclic
intermediate C, in which subsequent elimination of two protons
takes place to obtain aromaticity and to deliver the naphthalene
product 3. In this final step water molecule is expelled and triflic
acid catalyst is regenerated which participates in the next catalytic
cycle.
15e18). In the case of ketones also, reaction proceeded smoothly to
give the corresponding naphthalene derivatives. Importantly, tet-
rahydrophenanthrene derivatives could be prepared from 2-
phenylcyclohexanone 1i (entries 16 and 17). Anthracene deriva-
tive also could be made using this method by employing naph-
thylmethyl ketone 1j (entry 18). Though the reaction times are little
bit longer and yields are slightly lesser than that of reactions with
aldehydes, yields are generally good in all the studied cases. Here it
is interesting and noteworthy to mention that the same annulation
with ketones is very poor with HNTf2 catalytic system [14].
Although the substituents like -Cl, eF, -Br, and -OMe tolerate the
reaction conditions, -SiMe3 does not tolerate it and resulted in the
corresponding desilylated products (entries 19 and 20). Here, it is
significant to mention that HNTf2 catalysed annulation reaction of
-SiMe3 substituted phenyl acetylene led to degradation of starting
material but not to formation of corresponding naphthalene de-
rivative [14]. Arylalkynes only gave the corresponding naphthalene
derivatives and aliphatic alkynes did not participate in this annu-
lation reaction (entries 21 and 22). It emphasizes the key stabilizing
role of the aryl group of the arylalkynes in carbocation formation
during the course of the reaction (see mechanism, Scheme 1).
On the basis of the above experimental study and observations
of the reactions involving Brønsted acids as catalysts in literature
reports [14a,15], the following plausible catalytic cycle is proposed
for this Brønsted-acid-catalysed annulation reaction to explain the
2.3. Triflic acid catalysed intramolecular annulation approach to
synthesize 1-arylnaphthalenes
If in the same molecule, both arylmethyl carbonyl and ary-
lalkyne functions are tethered by an alkyl or alkoxy chain, aryl-
naphthalenes fused with ring systems could be prepared (Scheme
2). Encouraged by this, our attention was focused towards intra-
molecular version and thus triflic acid catalysed intramolecular
annulation reaction was developed to generate 1-arylnaphthalenes
fused with dihydrofuran, dihydropyran and cyclopentene rings.
Especially, the dihydrofuran fused naphthalenes are attractive and
important as they are the backbone skeleton of naturally occurring
biologically important lignan lactones [4e11] and thus there has
been decent interest among synthetic organic chemists in devel-
opment of lignan lactone synthesis [4,16].
For optimization of the intramolecular annulation reaction,
simple substrate 4a was chosen as this can easily be synthesized
from epoxycinnamyl alcohol in three steps. As in the case of
5

V. Gudla, M. Sudheer, C.J. Rao et al.
Tetrahedron xxx (xxxx) xxx
Scheme 2. Triflic acid catalysed intramolecular annulation reaction.
entry 8).
2.4. Scope of triflic acid catalyst in intramolecular 1-
arylnaphthalene synthesis
Scheme 1. A plausible reaction mechanism for the triflic acid catalysed
benzannulation.
Wide range of arylmethyl carbonyls tethered with arylalkyne
moiety 4a-4p prepared by Sonogashira coupling of a-aryl carbonyls
having propargyl or homopropargyl group with corresponding aryl
iodides using literature procedure [13d] were employed in this
Brønsted acid catalysed intramolecular reaction conditions
described in Table 3, entry 8 to examine the scope of the substrates.
And also, arylmethyl carbonyls tethered with arylalkyne moiety by
alkyl chain (4q and 4r) were prepared [13d] and subjected to triflic
acid catalysed reaction conditions. All the studied reactions went
on smoothly under reaction conditions and resulted in 1-
arylnaphthalenes fused with ring systems (5a-5r) in impressing
yields. Generally, reactions took between 30 min to 90 min. Table 4
represents the outcome of the study results. Ring fused 1-
arylnaphthalene derivatives could be prepared with wide range.
It is remarkable to observe that intramolecular reactions are highly
efficient compared to intermolecular reactions in terms of reaction
time, yield and conditions. By this intramolecular version, 1-
arylnaphthalenes fused with dihydrofuran (5a-5n), dihydropyran
(5o and 5p) and cyclopentene (5q and 5r) were synthesized suc-
cessfully. Ring fused naphthalenes having electron donating groups
and electron withdrawing groups could be prepared. Substituents
such as Cl, F, OMe and acetal could tolerate the reaction conditions.
Hydrofuran fused arylnaphthalene derivatives having electron
releasing groups like OMe on both aryl rings could be synthesized
efficiently. These compounds resemble more like the naturally
occurring arylnaphthalene lignan lactones. Benzylic oxidation of
these molecules would furnish 1-arylnaphthalene lignan lactones,
as reported in literature work [17,13d,12n]. Thus they serve as
scaffolds for 1-arylnaphthalene lactone lignans. As 1-
arylnaphthalene lactone lignans are known to have a range of
biological activities, furan-, and pyran-fused 1-arylnaphthalenes
might possess interesting biochemical properties.
intermolecular reactions, at the outset we performed the reaction
in CH2Cl2 at room temperature using 2 mol% of triflic acid (Table 3,
entry 1). To our delight, it resulted in 61% of the annulation product
1-phenylnaphthalene fused with dihydrofuran 5a along with 17% of
unreacted starting material 4a. Though there was no progress in the
reaction after 4 h, the reaction was allowed to stir for 24 h to check
for the completion. When catalyst loading was increased to 5 mol%,
yield was slightly improved to 65% along with 11% of 4a (entry 2).
The reaction with 10 mol% of catalyst resulted in 74% of cyclised
product and reaction led to completion (entry 3). Further increase
of the catalyst loading to 20 mol% did not increase the yield that
greatly (entry 4). Since 10 mol% of TfOH worked very well in the
reaction at RT, further optimization was carried out by changing the
other parameter i.e., solvent. When the reaction was run in 1,4-
dioxane solvent, yield of 4a was 73% (entry 5). In methanol and
THF solvents, the reactions were not clean and they resulted in
complex mixtures of products (entries 6 and 7). When the reaction
is performed in acetonitrile, the yield of 4a was improved sub-
stantially to 94% and reaction completed in 1 h (entry 8). When the
reaction was run in nitromethane, the yield was lesser compared to
that of acetonitrile reaction (entry 9). Hence, the appropriate con-
ditions for intramolecular naphthalene formation are: TfOH
(10 mol%) and acetonitrile as solvent at room temperature (Table 3,
Table 3
Optimization of reaction conditions for the intramolecular cyclisation.
3. Conclusions
Intermolecular and intramolecular regioselective synthesis of 1-
arylnaphthalenes from arylmethyl carbonyls and arylalkynes could
be achieved efficiently under triflic acid catalysed reaction condi-
tions. 20 mol% of catalyst is sufficient to promote the intermolec-
ular reaction while 10 mol% catalyst is highly efficient for
intramolecular version. This annulation reaction involves electro-
philic addition to the alkyne followed by benzannulation. The re-
action conditions tolerated wide range of substituents to produce
polysubstituted arylnaphthalenes. Using this method in intra-
molecular version, it has been shown that 1-arylnaphthalenes
fused with furan, pyran and cyclopentane could be made in
excellent yields. The compounds obtained might possess exciting
and encouraging biological activities as they are structurally similar
to 1-arylnaphthalene lactone lignan natural products.
Entry
Catalyst (mol%)
Solvent
Time (h)
Yielda (%)
1
2
3
4
5
6
7
8
9
2
5
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
1,4-dioxane
MeOH
THF
CH3CN
CH3NO2
24b
24b
6
6
4
4
4
1
4
61 (17)
65 (11)
74
10
20
10
10
10
10
10
75
73
__c
__c
94
69
a
Isolated yield. The percentage of recovered starting material 4a was denoted
within parentheses.
b
After 4 h, there was no progress in the reaction.
Complex reaction mixture.
c
6

V. Gudla, M. Sudheer, C.J. Rao et al.
Tetrahedron xxx (xxxx) xxx
Table 4
Scope of triflic acid catalyst in intramolecular 1-arylnaphthalene synthesis.a
7

V. Gudla, M. Sudheer, C.J. Rao et al.
Tetrahedron xxx (xxxx) xxx
(continued on next page)
8

V. Gudla, M. Sudheer, C.J. Rao et al.
Tetrahedron xxx (xxxx) xxx
Table 4 (continued)
a
Isolated yield.
4. Experimental section
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [18]:
d 7.39e7.53 (m,
9H), 7.85 (d, J ¼ 8.4 Hz, 1H), 7.88e7.91 (m, 2H) ppm. 13C NMR
4.1. General information
(100 MHz, CDCl3): d 125.3, 125.7, 126.0, 126.9, 127.2, 127.6, 128.2,
130.0, 131.6, 133.8, 140.2, 140.7 ppm.
Acetonitrile was dried using CaH2 and after distillation, it was
stored over 4 Å molecular sieves. For TLC, aluminium plates coated
with silica gel containing F254 indicator (bought from Merck) were
used and the spots were visualized by UV light and/or by heating
the plates sprayed with Seebach solution (phosphomolybdic acid
(2.5 g), Ce(SO4)2 (1.0 g), conc. H2SO4 (6 mL) and H2O (94 mL)).
Column chromatography was performed on silica gel 100e200
mesh, using ethyl acetate and hexanes mixture as eluent. The 1H
and 13C NMR spectra of the synthesized compounds were recorded
in a Bruker Avance 400 or 500 MHz NMR machine using their so-
lutions in CDCl3. The 1H NMR and 13C NMR were referred respec-
tively to TMS used as an internal standard and the central line of
CDCl3. Melting points were determined by using MR-VIS visual
melting range apparatus and are uncorrected.
4.2.2. 1-Phenyl-2-bromonaphthalene (3b)
It was obtained as light brown liquid in 62% yield. Rf ¼ 0.52 in
1:10 EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [13c]:
d 7.34e7.58
(m, 8H), 7.71 (s, 2H), 7.88 (d, J ¼ 8.0 Hz, 1H) ppm. 13C NMR
(100 MHz, CDCl3):
d 121.4, 126.0, 126.6, 126.7, 127.7, 128.3, 129.9,
130.1, 132.3, 133.8, 139.6, 139.8 ppm.
4.2.3. 2-Methyl-1-phenylnaphthalene (3c)
It was obtained as colorless liquid in 85% yield. Rf ¼ 0.54 in 1:10
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [13b]:
d 2.25 (s, 3H),
7.27e7.35 (m, 3H), 7.39e7.46 (m, 4H), 7.51 (t, J ¼ 7.6 Hz, 2H), 7.79 (d,
J ¼ 8.4 Hz, 1H), 7.85 (d, J ¼ 7.6 Hz, 1H) ppm. 13C NMR (100 MHz,
CDCl3):
d 20.8, 124.7, 125.8, 126.1, 127.0, 127.2, 127.7, 128.4, 128.6,
Triflic acid was purchased from Aldrich. Carbonyl compounds
1a, 1b, 1d, 1f, 1h, 1i and arylalkynes 2a-2d, 2f were purchased from
Aldrich and 2k from TCI Chemicals. Carbonyl compounds 1c, 1e, 1g,
and 1j and alkynes 2e, 2g-2j, 2l and 2m were prepared by following
standard procedures. Propargyloxy (4a-4n), homopropargyloxy (4o
and 4p) and alkyl tethered (4q and 4r) arylalkynes were prepared
using the procedures described in ref.13d.
130.1, 131.9, 132.9, 133.1, 138.1, 139.8 ppm.
4.2.4. 2-Methyl-1,4-diphenylnaphthalene (3d)
It was obtained as colorless liquid in 63% yield. Rf ¼ 0.49 in 1:10
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [13b]:
d 2.26 (s, 3H),
7.31e7.34 (m, 4H), 7.37 (s, 1H), 7.42e7.56 (m, 9H), 7.88e7.91 (m, 1H)
ppm. 13C NMR (100 MHz, CDCl3):
d
20.8, 124.8, 125.6, 125.9, 126.5,
127.0, 127.2, 128.2, 128.4, 129.7, 130.1, 130.2, 132.6, 133.3, 137.8,
139.4, 139.8, 140.8 ppm.
4.2. General procedure for triflic acid catalysed intermolecular
cyclisation for the synthesis of naphthalenes 3
4.2.5. 1-Butyl-4-phenylnaphthalene (3e)
To the solution of a-aryl aldehyde or ketone 1 (1.0 equiv.) and
It was obtained as colorless liquid in 81% yield. Rf ¼ 0.57 in 1:10
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [13b]:
d
1.00 (t, J ¼ 7.6
arylalkyne 2 (1.2 equiv.) in dry acetonitrile (3 mL/1 mmol of 1),
triflic acid (20 mol%) was added at RT under N2 atmosphere. The
contents in the flask were allowed to stir at RT and the reaction was
monitored by TLC. After completion of the reaction, CH3CN was
evaporated and crude mixture was directly loaded on silica gel
column which was eluted with ethyl acetate and hexanes mixture
to get pure naphthalene derivative 3.
HZ, 3H), 1.50 (sext, J ¼ 7.6 Hz, 2H), 1.79 (quint, J ¼ 7.6 Hz, 2H), 3.11 (t,
J ¼ 7.6 Hz, 2H), 7.32e7.53 (m, 9H), 7.91 (d, J ¼ 8.4 Hz, 1H), 8.11 (d,
J ¼ 8.4 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3):
d 14.0, 22.9, 32.9,
33.0, 124.1, 125.4, 125.5, 126.6, 126.8, 127.0, 127.2, 128.2, 130.2, 132.0,
132.1, 138.5, 138.6, 141.1 ppm.
4.2.6. 1-Butyl-3,4-diphenylnaphthalene (3f)
4.2.1. 1-Phenylnaphthalene (3a)
It was obtained as colorless liquid in 83% yield. Rf ¼ 0.56 in 1:10
It was obtained as colorless liquid in 71% yield. Rf ¼ 0.53 in 1:10
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [19]:
d
0.99 (t, J ¼ 7.6 Hz,
9

V. Gudla, M. Sudheer, C.J. Rao et al.
Tetrahedron xxx (xxxx) xxx
3H), 1.53 (sext, J ¼ 7.6 Hz, 2H), 1.83 (quint, J ¼ 7.6 Hz, 2H), 3.15 (t,
J ¼ 7.6 Hz, 2H), 7.13e7.20 (m, 7H), 7.26e7.30 (m, 3H), 7.39 (t,
J ¼ 7.6 Hz, 1H), 7.43 (s, 1H), 7.51 (t, J ¼ 7.6 Hz, 1H), 7.69 (d, J ¼ 8.4 Hz,
4.2.13. 7-Fluoro-1-(4-methoxyphenyl)naphthalene (3m)
It was obtained as colorless liquid in 69% yield. Rf ¼ 0.44 in 1:10
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [12l]:
3.89 (s, 3H),
d
1H), 8.12 (d, J ¼ 8.4 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3):
d
14.0,
7.02e7.05 (m, 2H), 7.26 (td, J ¼ 8.4, 2.4 Hz, 1H), 7.39e7.49 (m, 4H),
23.0, 32.9, 33.0, 123.8, 125.4, 125.7, 126.1, 126.6, 127.5, 127.6, 127.7,
128.3, 130.1, 131.2, 131.6, 133.1, 135.9, 137.9, 138.4, 139.3, 142.2 ppm.
7.54 (dd, J ¼ 11.2, 2.4 Hz,1H), 7.82 (d, J ¼ 8.0 Hz,1H), 7.88 (dd, J ¼ 8.8,
6.0 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3):
d 55.4, 109.5 (d,
J ¼ 21.8 Hz), 113.9, 116.0 (d, J ¼ 25.3 Hz), 124.6, 127.2, 127.7, 130.6 (d,
J ¼ 8.8 Hz), 130.8, 130.9, 132.6, 132.8 (d, J ¼ 8.6 Hz), 139.4 (d,
J ¼ 5.0 Hz), 159.1, 160.8 (d, J ¼ 243.5 Hz) ppm.
4.2.7. 2-Hexyl-1-(4-fluorophenyl)-4-methylnaphthalene (3g)
It was obtained as colorless liquid in 78% yield. Rf ¼ 0.56 in 1:10
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [12l]:
d
0.82 (t, J ¼ 7.2 Hz,
3H), 1.16e1.21 (m, 6H), 1.47 (quint, J ¼ 7.6 Hz, 2H), 2.44 (t, J ¼ 7.6 Hz,
2H), 2.70 (s, 3H), 7.12e7.22 (m, 5H), 7.28e7.35 (m, 2H), 7.40e7.43
(m, 1H), 7.97 (d, J ¼ 8.4 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3):
4.2.14. 6-Methyl-5-phenylnaphtho[2,3-d][1,3]dioxole (3n)
It was obtained as colorless liquid in 73% yield. Rf ¼ 0.41 in 1:10
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [12l]:
d 2.17 (s, 3H), 5.95
d
14.0, 19.5, 22.5, 29.2, 31.5, 33.7, 115.1 (d, J ¼ 21.1 Hz), 123.9, 124.7,
(s, 2H), 6.68 (s, 1H), 7.11 (s, 1H), 7.22e7.27 (m, 3H), 7.41e7.42 (m,
1H), 7.46e7.50 (m, 2H), 7.59 (d, J ¼ 8.4 Hz, 1H) ppm. 13C NMR
125.5, 126.8, 128.4, 131.0, 132.1 (d, J ¼ 7.0 Hz), 133.3, 133.7, 135.0,
135.5, 138.0, 162.0 (d, J ¼ 243.8 Hz) ppm.
(100 MHz, CDCl3):
d 20.7, 100.9, 102.7, 103.7, 126.2, 127.0, 128.5,
128.8, 130.0, 131.7, 137.8, 140.1, 146.6, 147.6 ppm.
4.2.8. 1-(2,4-Dichlorophenyl)-4-methylnaphthalene (3h)
It was obtained as colorless liquid in 74% yield. Rf ¼ 0.57 in 1:10
4.2.15. 3-Methyl-1-phenylnaphthalene (3o)
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [12l]:
d 2.72 (s, 3H),
It was obtained as colorless liquid in 57% yield. Rf ¼ 0.51 in 1:10
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [20]:
d 2.55 (s, 3H), 7.29
7.17e7.26 (m, 2H), 7.30e7.41 (m, 3H), 7.45 (d, J ¼ 8.0 Hz,1H), 7.50 (d,
J ¼ 7.6 Hz, 1H), 7.54 (s, 1H), 8.04 (d, J ¼ 8.4 Hz, 1H) ppm. 13C NMR
(s, 1H), 7.34e7.40 (m, 1H), 7.43e7.50 (m, 6H), 7.64 (s, 1H), 7.82 (d,
J ¼ 8.4 Hz, 1H), 7.86 (d, J ¼ 8.4 Hz, 1H) ppm. 13C NMR (100 MHz,
(100 MHz, CDCl3):
d 19.6, 124.5, 125.8, 125.9, 126.1, 126.8, 126.9,
129.3, 131.4, 132.5, 133.0, 133.9, 134.5, 134.9, 135.0, 138.1 ppm.
CDCl3):
d 21.6, 125.1, 125.8, 126.6, 127.2, 127.6, 128.2, 129.2, 129.9,
130.0, 134.1, 134.9, 140.1, 140.8 ppm.
4.2.9. 7-Chloro-1,2-diphenylnaphthalene (3i)
It was obtained as colorless liquid in 65% yield. Rf ¼ 0.53 in 1:10
4.2.16. 9-Phenyl-1,2,3,4-tetrahydrophenanthrene (3p)
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [12l]:
d 7.10e7.14 (m,
It was obtained as colorless liquid in 65% yield. Rf ¼ 0.56 in 1:10
7H), 7.26e7.28 (m, 3H), 7.40 (d, J ¼ 8.4 Hz, 1H), 7.54 (d, J ¼ 8.4 Hz,
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [13c]:
d 1.87e1.93 (m,
1H), 7.64 (s, 1H), 7.80 (d, J ¼ 8.4 Hz, 1H), 7.85 (d, J ¼ 8.4 Hz, 1H) ppm.
2H), 1.98e2.04 (m, 2H), 2.94 (t, J ¼ 6.0 Hz, 2H), 3.16 (t, J ¼ 6.4 Hz,
2H), 7.16 (s, 1H), 7.35e7.42 (m, 2H), 7.46e7.52 (m, 5H), 7.86 (d,
J ¼ 8.0 Hz, 1H), 8.03 (d, J ¼ 8.4 Hz, 1H) ppm. 13C NMR (100 MHz,
13C NMR (100 MHz, CDCl3):
d 125.6, 126.4, 126.6, 127.0, 127.4, 127.6,
128.0, 128.6, 129.4, 130.0, 131.0, 131.3, 132.2, 133.4, 136.9, 138.2,
139.4, 141.5 ppm.
CDCl3): d 22.9, 23.3, 25.7, 30.4, 123.0, 124.8, 125.7, 126.5, 127.0, 128.1,
129.2, 130.1, 130.3, 131.1, 132.8, 133.8, 137.9, 141.0 ppm.
4.2.10. 7-Chloro-1-(4-methoxyphenyl)-2-propylnaphthalene (3j)
It was obtained as colorless liquid in 66% yield. Rf ¼ 0.49 in 1:10
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [12l]:
d
0.82 (t, J ¼ 7.6 Hz,
4.2.17. 10-Methyl-9-phenyl-1,2,3,4-tetrahydrophenanthrene (3q)
It was obtained as colorless liquid in 78% yield. Rf ¼ 0.57 in 1:10
3H), 1.48e1.57 (m, 2H), 2.49 (t, J ¼ 7.6 Hz, 2H), 3.91 (s, 3H), 7.03 (d,
J ¼ 8.4 Hz, 2H), 7.15 (d, J ¼ 8.8 Hz, 2H), 7.33 (dd, J ¼ 8.4, 2.0 Hz, 1H),
7.36 (s, 1H), 7.41 (d, J ¼ 8.4 Hz, 1H), 7.75 (dd, J ¼ 8.4, 1.6 Hz, 2H) ppm.
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [13c]:
d 1.96e1.97 (m,
4H), 2.10 (s, 3H), 2.83 (t, J ¼ 5.2 Hz, 2H), 3.22 (t, J ¼ 5.2 Hz, 2H),
13C NMR (100 MHz, CDCl3):
d 14.1, 24.6, 35.8, 55.3, 113.8, 125.4,
7.25e7.33 (m, 4H), 7.41e7.44 (m, 2H), 7.49 (t, J ¼ 7.2 Hz, 2H), 8.02 (d,
J ¼ 8.4 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3):
d 17.4, 22.8, 23.2,
26.5, 28.3, 122.5, 124.6, 124.8, 126.7, 126.9, 128.3, 130.5, 130.8, 131.1,
131.3, 132.8, 134.0, 136.5, 140.9 ppm.
125.6, 127.0, 127.9, 129.2,130.1, 130.8, 131.3, 131.5, 134.2,137.0, 139.4,
158.7 ppm.
4.2.11. 7-Chloro-1-(2,4-dichlorophenyl)naphthalene (3k)
4.2.18. 2-Hexyl-3-methyl-1-m-tolylanthracene (3r)
It was obtained as colorless liquid in 68% yield. Rf ¼ 0.58 in 1:10
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [12l]:
d 7.26 (d,
It was obtained as colorless liquid in 56% yield. Rf ¼ 0.49 in 1:10
EtOAc/hexanes. 1H NMR (500 MHz, CDCl3) [12l]:
d
0.83 (t, J ¼ 7.0 Hz,
J ¼ 8.4 Hz, 1H), 7.36 (dd, J ¼ 7.6, 1.6 Hz, 2H), 7.42 (d, J ¼ 8.8 Hz, 2H),
3H), 1.14e1.22 (m, 6H), 1.34e1.40 (m, 2H), 2.40 (s, 3H), 2.45e2.50
(m, 2H), 2.57 (s, 3H), 7.00e7.04 (m, 1H), 7.10e7.12 (m, 2H),
7.28e7.36 (m, 3H), 7.40 (t, J ¼ 7.2 Hz, 1H), 7.64 (dd, J ¼ 11.6, 8.8 Hz,
2H), 7.70 (s, 1H), 7.74 (d, J ¼ 8.0 Hz, 1H) ppm. 13C NMR (100 MHz,
7.52 (t, J ¼ 7.6 Hz, 1H), 7.57 (d, J ¼ 1.6 Hz, 1H), 7.83 (d, J ¼ 8.8 Hz, 1H),
7.87 (d, J ¼ 8.4 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3):
d 124.4,
125.5,127.0,127.1,128.3,128.4,129.6,129.9,131.7,132.2,132.4,132.7,
134.5, 134.8, 135.5, 137.0 ppm.
CDCl3):
d 14.0, 20.3, 21.6, 22.4, 29.7, 30.1, 31.0, 31.2, 124.9, 125.1,
127.0, 127.2, 127.5,127.7, 128.5,128.9,129.8,130.5,131.0,131.6, 133.5,
135.0, 138.6, 139.2, 140.1, 143.6 ppm.
4.2.12. 2-(2-Bromoethyl)-7-fluoro-1-p-tolylnaphthalene (3l)
It was obtained as colorless liquid in 77% yield. Rf ¼ 0.43 in 1:10
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [12l]:
d 2.46 (s, 3H), 3.11
(t, J ¼ 8.0 Hz, 2H), 3.41 (t, J ¼ 8.0 Hz, 2H), 6.99 (dd, J ¼ 11.2, 2.0 Hz,
4.2.19. 1-(3,5-Dimethylphenyl)-4-phenylnaphthalene (3s)
1H), 7.12 (d, J ¼ 8.0 Hz, 2H), 7.19 (td, J ¼ 8.4, 2.8 Hz, 1H), 7.30 (d,
It was obtained as colorless liquid in 66% yield. Rf ¼ 0.47 in 1:10
J ¼ 8.0 Hz, 2H), 7.38 (d, J ¼ 8.4 Hz, 1H), 7.78e7.82 (m, 2H) ppm. 13
C
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [12l]:
d 2.38 (s, 6H), 7.05
NMR (100 MHz, CDCl3):
d
21.3, 32.1, 37.3, 110.1 (d, J ¼ 21.9 Hz), 115.7
(s, 1H), 7.13 (s, 2H), 7.37e7.42 (m, 4H), 7.44e7.51 (m, 4H), 7.92e7.99
(d, J ¼ 25.2 Hz), 126.6, 127.5, 129.4, 129.8, 130.0 (d, J ¼ 8.8 Hz), 134.3
(d, J ¼ 8.4 Hz), 135.0 (d, J ¼ 5.9 Hz), 137.3, 138.6 (d, J ¼ 5.7 Hz), 160.8
(d, J ¼ 243.8 Hz) ppm.
(m, 2H) ppm. 13C NMR (100 MHz, CDCl3):
d
21.4, 125.70, 125.74,
126.3, 126.4, 126.5, 127.2, 128.0, 128.2, 128.8, 130.1, 131.9, 132.0,
137.7, 139.6, 140.1, 140.7, 140.9 ppm.
10

V. Gudla, M. Sudheer, C.J. Rao et al.
Tetrahedron xxx (xxxx) xxx
4.3. General procedure for triflic acid catalysed intramolecular
cyclisation for the synthesis of naphthalenes 5
133.5, 133.8, 135.6, 137.6, 137.9 ppm.
4.3.7. 6,8-Dichloro-4-o-tolyl-1,3-dihydronaphtho[2,3-c]furan (5g)
It was obtained in 90% yield as colorless liquid. Rf ¼ 0.41 in 1:10
Triflic acid (10 mol%) was added to the solution of compound 4
in dry acetonitrile (5mL/1 mmol of 4) and the resulting reaction
mixture was allowed to stir at room temperature. The reaction
progress was monitored by TLC. After completion of the reaction,
solvent was evaporated and crude was purified by column chro-
matography (silica gel, hexanes/EtoAc) to furnish the pure com-
pound 5.
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [13d]:
d 1.96 (s, 3H), 4.79
(d, J ¼ 13.6 Hz, 1H), 4.94 (d, J ¼ 13.6 Hz, 1H), 5.33 (s, 2H), 7.12 (d,
J ¼ 7.2 Hz,1H), 7.26e7.40 (m, 4 H), 7.55 (d, J ¼ 1.6 Hz,1H), 8.13 (s,1H)
ppm. 13C NMR (100 MHz, CDCl3):
d 19.6, 72.8, 73.5, 115.4, 123.6,
126.3, 126.6, 128.5, 129.2, 129.4, 130.5, 130.9, 131.9, 133.0, 133.4,
136.1, 136.2, 139.0, 139.3 ppm.
4.3.1. 4-Phenyl-1,3-dihydronaphtho[2,3-c]furan (5a)
It was obtained in 94% yield as colorless liquid. Rf ¼ 0.36 in 1:10
4.3.8. 6-Chloro-4-(3,4,5-trimethoxyphenyl)-1,3-dihydronaphtho
[2,3-c]furan (5h)
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [12f]:
d 5.01 (s, 2H), 5.28
(s, 2H), 7.33e7.39 (m, 3H), 7.41e7.52 (m, 4H), 7.66e7.68 (m, 2H),
It was obtained in 88% yield as coloress solid, m.p. 151e152 ꢀC
(lit.[13d] 150e151 ꢀC). Rf ¼ 0.33 in 1:3 EtOAc/hexanes. 1H NMR
7.85 (d, J ¼ 8.0 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3):
d 72.8, 73.3,
118.8, 125.6, 125.7, 127.6, 128.0, 128.6, 129.4, 131.7, 132.5, 133.6,
136.8, 137.6, 138.1 ppm.
(400 MHz, CDCl3) [13d]:
3H), 5.05 (s, 2H), 5.27 (s, 2H), 6.53 (d, J ¼ 1.6 Hz, 2H), 7.40e7.43 (m,
d
3.85 (d, J ¼ 1.2 Hz, 6H), 3.97 (d, J ¼ 2.0 Hz,
1H), 7.65 (s, 1H), 7.71 (s, 1H), 7.77e7.80 (m, 1H) ppm. 13C NMR
4.3.2. 4-(4-Methoxyphenyl)-1,3-dihydronaphtho[2,3-c]furan (5b)
It was obtained in 96% yield as colorless liquid. Rf ¼ 0.25 in 1:10
(100 MHz, CDCl3): d 56.1, 60.9, 72.8, 73.2, 106.2, 118.6, 124.5, 126.5,
129.5, 131.8, 131.9, 132.5, 132.8, 137.4, 137.9, 138.0, 153.4 ppm.
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [12f]:
d 3.88 (s, 3H), 5.02
(s, 2H), 5.28 (s, 2H), 7.02 (d, J ¼ 8.8 Hz, 2H), 7.27 (d, J ¼ 8.8 Hz, 2H),
7.36 (t, J ¼ 7.2 Hz, 1H), 7.44 (t, J ¼ 7.2 Hz, 1H), 7.66 (s, 1H), 7.71 (d,
J ¼ 8.4 Hz, 1H), 7.84 (d, J ¼ 8.0 Hz, 1H) ppm. 13C NMR (100 MHz,
4.3.9. 4-(Benzo[d][1,3]dioxol-5-yl)-6-chloro-1,3-dihydronaphtho
[2,3-c]furan (5i)
It was obtained in 92% yield as yellow colored liquid. Rf ¼ 0.51 in
CDCl3):
d 55.3, 72.9, 73.4, 114.0, 118.47, 118.54, 125.5, 125.6, 128.0,
1:3 EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [13d]:
d 5.01 (s, 2H),
130.2, 130.6, 132.0, 132.3, 133.7, 137.0, 137.6, 159.0 ppm.
5.25 (s, 2H), 6.05 (d, J ¼ 4.4 Hz, 1H), 6.06 (d, J ¼ 4.4 Hz, 1H),
6.75e6.78 (m, 2H), 6.94 (d, J ¼ 8.0 Hz, 1H), 7.38 (d, J ¼ 8.8 Hz, 1H),
7.62 (s, 1H), 7.67 (s, 1H), 7.76 (d, J ¼ 8.4 Hz, 1H) ppm. 13C NMR
4.3.3. 6-Fluoro-4-(4-fluorophenyl)-1,3-dihydronaphtho[2,3-c]furan
(5c)
(100 MHz, CDCl3): d 72.8, 73.2, 101.3, 108.7, 109.8, 118.6, 122.8, 124.5,
It was obtained in 92% yield as light yellow colored semi-solid.
126.5, 129.5, 130.8, 131.5, 131.8, 131.9, 132.8, 138.0, 138.2, 147.3,
147.9 ppm.
Rf ¼ 0.36 in 1:5 EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [12l]:
d
5.00 (s, 2H), 5.28 (s, 2H), 7.19e7.33 (m, 6H), 7.69 (s, 1H), 7.84e7.87
(m, 1H) ppm. 13C NMR (100 MHz, CDCl3):
d 72.8, 73.2, 109.0 (d,
J ¼ 22.0 Hz), 115.9 (d, J ¼ 21.3 Hz), 116.0 (d, J ¼ 25.2 Hz), 119.0, 130.3
(d, J ¼ 8.9 Hz), 130.6, 131.0 (d, J ¼ 7.7 Hz), 132.8 (d, J ¼ 8.5 Hz), 133.4,
137.1, 138.2, 160.9 (d, J ¼ 244.0 Hz), 162.4 (d, J ¼ 245.7 Hz) ppm.
4.3.10. 4-(3,4-Dimethoxyphenyl)-6-methoxy-1,3-dihydronaphtho
[2,3-c]furan (5j)
It was obtained in 97% yield as colorless liquid. Rf ¼ 0.46 in 1:1
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [13d]:
d 3.72 (s, 3H), 3.85
4.3.4. 4-(4-Chlorophenyl)-6-fluoro-1,3-dihydronaphtho[2,3-c]furan
(5d)
(s, 3H), 3.95 (s, 3H), 4.99 (d, J ¼ 13.6 Hz,1H), 5.04 (d, J ¼ 13.6 Hz,1H),
5.23 (s, 2H), 6.89e6.91 (m, 2H), 6.98 (d, J ¼ 8.8 Hz, 1H), 7.06 (d,
J ¼ 2.0 Hz, 1H), 7.12 (dd, J ¼ 9.2, 2.4 Hz, 1H), 7.56 (s, 1H), 7.72 (d,
It was obtained in 94% yield as colorless liquid. Rf ¼ 0.40 in 1:5
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [13d]:
d
4.99 (s, 2H), 5.27
J ¼ 8.8 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3):
d 55.0, 55.7, 55.8,
(s, 2H), 7.22e7.30 (m, 4H), 7.50 (d, J ¼ 8.0 Hz, 2H), 7.70 (s, 1H),
72.8, 73.2, 104.2, 111.2, 112.4, 117.8, 118.3, 121.5, 129.0, 129.3, 130.6,
131.0, 132.9, 135.2, 137.3, 148.2, 148.8, 157.5 ppm.
7.84e7.87 (m, 1H) ppm. 13C NMR (100 MHz, CDCl3):
d
72.7, 73.2,
109.0 (d, J ¼ 22.1 Hz), 116.1 (d, J ¼ 25.2 Hz), 119.1, 129.1, 130.3 (d,
J ¼ 8.9 Hz),130.6,130.7,132.6 (d, J ¼ 8.5 Hz),134.0,136.0,137.1,138.1,
160.9 (d, J ¼ 244.3 Hz) ppm.
4.3.11. 4-(Benzo[d][1,3]dioxol-5-yl)-6-methoxy-1,3-
dihydronaphtho[2,3-c]furan (5k)
It was obtained in 98% yield as colorless liquid. Rf ¼ 0.36 in 1:3
4.3.5. 6-Chloro-4-(4-chlorophenyl)-1,3-dihydronaphtho[2,3-c]
furan (5e)
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [13d]:
d 3.72 (s, 3H), 4.98
(s, 2H), 5.21 (s, 2H), 5.99 (s, 1H), 6.02 (s, 1H), 6.77e6.81 (m, 2H), 6.91
(d, J ¼ 7.6 Hz, 1H), 7.02 (s, 1H), 7.11 (dd, J ¼ 8.8, 2.4 Hz, 1H), 7.54 (s,
It was obtained in 90% yield as colorless liquid. Rf ¼ 0.42 in 1:10
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [12f]:
d 4.97 (s, 2H), 5.25
1H), 7.70 (d, J ¼ 8.8 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3):
d 55.1,
(s, 2H), 7.24e7.28 (m, 2H), 7.40 (dd, J ¼ 8.8, 2.0 Hz, 1H), 7.47e7.50
72.8, 73.2, 101.1, 104.3, 108.5, 109.7, 117.8, 118.4, 122.6, 129.0, 129.3,
130.9, 131.8, 133.0, 135.2, 137.5, 146.9, 147.8, 157.6 ppm.
(m, 2H), 7.57 (d, J ¼ 2.0 Hz, 1H), 7.65 (s, 1H), 7.78 (d, J ¼ 8.8 Hz, 1H)
ppm. 13C NMR (100 MHz, CDCl3):
d 72.7, 73.2, 119.0, 119.1, 124.3,
126.6, 129.1, 129.6, 130.6, 130.7, 131.9, 132.0, 132.4, 134.0, 135.7,
138.06, 138.14 ppm.
4.3.12. 5-(3,4-Dimethoxy-phenyl)-6,8-dihydro-furo[30,4’:6,7]
naphtha[2,3-d][1,3]dioxole (5l)
4.3.6. 4-(Naphthalen-1-yl)-1,3-dihydronaphtho[2,3-c]furan (5f)
It was obtained in 92% yield as colorless liquid. Rf ¼ 0.43 in 1:10
It was obtained in 92% yield as colorless liquid. Rf ¼ 0.30 in 1:3
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [13d]:
d 3.86 (s, 3H), 3.96
EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [21]:
d
4.72 (d,
(s, 3H), 4.98 (s, 2H), 5.24 (s, 2H), 6.00 (s, 2H), 6.83 (s, 1H), 6.87 (d,
J ¼ 13.2 Hz, 1H), 4.92 (d, J ¼ 13.2 Hz, 1H), 5.34 (s, 2H), 7.26e7.34 (m,
J ¼ 8.4 Hz, 1H), 6.99 (d, J ¼ 8.0 Hz, 1H), 7.01 (s, 1H), 7.13 (s, 1H), 7.49
4H), 7.42e7.50 (m, 3H), 7.57e7.61 (m,1H), 7.79 (s,1H), 7.91e7.98 (m,
(s, 1H) ppm. 13C NMR (100 MHz, CDCl3):
d 55.9, 73.0, 73.4, 101.1,
3H) ppm. 13C NMR (100 MHz, CDCl3):
d
72.8, 73.4, 119.1, 125.5, 125.7,
102.2, 103.9, 111.3, 112.4, 117.8, 121.6, 129.0, 130.7, 130.9, 131.8, 135.5,
136.1, 147.3, 147.7, 148.4, 148.9 ppm.
125.8, 126.0, 126.4, 127.3, 128.0, 128.3, 128.4, 130.6, 131.8, 132.6,
11

V. Gudla, M. Sudheer, C.J. Rao et al.
Tetrahedron xxx (xxxx) xxx
4.3.13. 5,7-Dichloro-9-(4-chlorophenyl)-1-methyl-1,3-
dihydronaphtho[2,3-c]furan (5m)
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
It was obtained in 91% yield as yellow colored liquid. Rf ¼ 0.46 in
1:10 EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [13d]:
d 1.04 (d,
Acknowledgments
J ¼ 6.4 Hz, 3H), 5.21 (d, J ¼ 13.2 Hz,1H), 5.32 (d, J ¼ 13.2 Hz,1H), 5.41
(q, J ¼ 6.4 Hz, 1H), 7.21e7.26 (m, 2H), 7.43 (s, 1H), 7.50e7.55 (m, 3H),
Vanajakshi G. thanks Dr. DSK PDF Scheme (UGC), India for
postdoctoral fellowship and research grants provided for work. Ch.
Joginarayana Rao thanks TEQIP Phase-III, Govt. of India for financial
research assistantship. The authors thank Andhra University,
Visakhapatnam, India for providing facilities to carry out research
work.
8.11 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3):
d 20.4, 71.4, 79.6, 116.0,
123.8, 126.6, 128.4, 128.7, 129.4, 130.5, 130.8, 131.4, 131.8, 133.0,
133.7, 134.3, 135.0, 139.5, 142.8 ppm.
4.3.14. 9-Phenyl-1-propyl-1,3-dihydronaphtho[2,3-c]furan (5n)
It was obtained in 89% yield as light yellow colored liquid.
Rf ¼ 0.42 in 1:10 EtOAc/hexanes. 1H NMR (400 MHz, CDCl3) [12l]:
Appendix A. Supplementary data
d
0.67 (t, J ¼ 7.2 Hz, 3H), 1.13e1.31 (m, 4H), 5.23 (d, J ¼ 12.4 Hz, 1H),
5.29 (d, J ¼ 12.8 Hz, 1H), 5.42e5.44 (m, 1H), 7.30e7.37 (m, 3H),
7.43e7.51 (m, 4H), 7.63 (d, J ¼ 8.4 HZ, 1H), 7.67 (s, 1H), 7.85 (d,
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tet.2021.132214.
J ¼ 8.0 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3):
d 13.8, 18.0, 36.0,
71.8, 83.3, 118.7, 125.5, 125.8, 127.6, 127.9, 128.0, 128.96, 129.11,
130.4, 132.1, 133.0, 133.5, 137.8, 138.2, 139.1 ppm.
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68.7, 122.4, 125.3, 125.4, 126.0, 127.2, 127.3, 128.5, 129.5, 130.0, 131.7,
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It was obtained in 96% yield as colorless liquid. Rf ¼ 0.59 in 1:5
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2.38 (s, 6H), 2.69
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CDCl3):
d
21.4, 28.0, 65.9, 68.6, 109.5 (d, J ¼ 21.7 Hz), 115.7 (d,
J ¼ 25.7 Hz), 122.0, 127.5, 128.8, 129.0, 129.6 (d, J ¼ 8.8 Hz), 130.5,
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d 2.02e2.07
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d 25.6, 32.2, 33.1, 55.4, 111.1, 120.5, 121.8, 124.5,
124.6, 125.7, 127.6, 128.0, 128.7, 131.0, 131.7, 133.1, 142.4, 142.6,
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Declaration of competing interest
ꢀ
ꢁ
ꢀ
ꢁ
ꢂꢀ ꢀ
(e) J. Storch, J. Sýkora, J. Cermak, J. Karban, I. Císarova, A. Ruzicka, J. Org. Chem.
The authors declare that they have no known competing
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