One-Pot Zn/CuI/TFA-catalyzed domino three-component-carbocyclization reaction involving Biphenyl-2-carbaldehydes/Alkynes/Piperidine: Allenes-mediated construction of phenanthrenes

Article abstract of DOI:10.1021/jo201942r

A one-pot protocol involving Zn/CuI/TFA-catalyzed domino three-component and subsequent carbocyclization reactions is described. The reaction proceeds via formation of propargyl amines from biphenyl-2-carbaldehydes/terminal alkynes/piperidine followed by

Full text of DOI:10.1021/jo201942r

Article
pubs.acs.org/joc
One-Pot Zn/CuI/TFA-Catalyzed Domino Three-Component−
Carbocyclization Reaction Involving Biphenyl-2-carbaldehydes/
Alkynes/Piperidine: Allenes-Mediated Construction of
Phenanthrenes
Mohammad Saifuddin, Piyush K. Agarwal, and Bijoy Kundu*
Medicinal & Process Chemistry Division, Central Drug Research Institute, CSIR, Lucknow 226 001, India
S
* Supporting Information
ABSTRACT: A one-pot protocol involving Zn/CuI/TFA-catalyzed domino three-component and subsequent carbocyclization
reactions is described. The reaction proceeds via formation of propargyl amines from biphenyl-2-carbaldehydes/terminal
alkynes/piperidine followed by the elimination of piperidine and ring closure to furnish phenanthrene derivatives in good yields.
The strategy involves C(sp)-H activation−CH functionalization with imine-alkyne activation−1,5 hydride shift−β-elimination of
piperidine−allene formation−6π cycloaddition−isomerization domino sequence. Evidence for the involvement of allenes as an
intermediate during carbocyclization is discussed.
three-component−carbocyclization domino reaction by em-
ploying biphenyl-2-carbaldehydes, terminal alkynes, and piper-
idine as reactants. The studies are part of our ongoing studies
for the synthesis of annulated polyheterocycles in one pot.7
INTRODUCTION
■
Phenanthrene skeletons are ubiquitous substructures in many
natural1 and synthetic products with applications to medicinal
chemistry and material sciences (polycyclic aromatic electronic
materials).2 Among a variety of methods described in the
literature for the phenanthrene class of compounds, reports
dealing with the [4 + 2] cycloaddition/benzannulation reaction
with functionalized tethered biaryls and alkynes have drawn
significant attention.3 In general, these multistep strategies
involve transition-metal-catalyzed [4 + 2] annulation of
halobiaryls/2-phenylbenzoic acid/2-biaryl Grignard reagent
with alkynes. In yet another multistep strategy involving
alkynes, 9-substituted phenanthrenes were obtained by
subjecting 2-alkynylated biphenyl derivatives to an intra-
molecular hydroarylation in the presence of Au4/DBU5 as
catalysts. However, to the best of our knowledge there are no
reports dealing with multicomponent reaction (MCR)-based
protocols with alkynes as one of the components leading to the
synthesis of phenanthrenes. Motivated by these observations,
we envisaged that propargyl amines generated from biphenyl-2-
carbaldehyde/alkynes/amines in MCR format could be further
subjected to an intramolecular carbocyclization following
activation of the internal alkyne to afford phenanthrenes. In
recent years, great efforts have been made to develop strategies
involving sequenced MCRs/post-MCR modifications either in
one pot or in tandem with the view to generate chemprobes
with increased architectural complexity and diversity.6 In this
article, we report a one-pot protocol for 9/10-substituted
phenanthrenes through the intermediacy of allenes following a
RESULTS AND DISCUSSION
■
We commenced our studies by examining the ability of the
propargyl amine 3′-4′-dimethoxy-1-(1-biphenyl-2-yl-3-(4-(tert-
butyl)-phenyl-prop-2-ynyl)-piperidine 1a to undergo intramole-
cular cyclization. Intermediate 1a was obtained by treating
biphenyl-2-carbaldehyde with 4-tert-butyl-phenylacetylene and
piperidine in the presence of Zn dust in acetonitrile under
reflux as described elsewhere in the literature.8 To enforce
carbocyclization in the resulting propargyl amine 1a, we
envisioned that activating the alkyne moiety using iodine-
derived electrophilic reagents,9 Bronsted/Lewis acids,10 or
transition metals11 as a catalyst may initiate a ring closure via
C−C bond formation.
For our studies, we selected transition metals as a catalyst of
choice and were especially attracted toward zinc and copper
salts as they have been traditionally used to activate the
alkynes.12 We screened a variety of copper and zinc salts as
catalysts for facilitating cyclization, and the results of our
optimization studies have been summarized in Table 1 (entries
1−19). Attempts to cyclize 1a in either in the absence of any
metal catalyst (entry 1) or in the presence CuI or Zn dust/ZnI2
Received: September 24, 2011
Published: November 4, 2011
© 2011 American Chemical Society
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Table 1. Optimization of Reaction Condition for the
was ineffective in promoting cyclization (entries 7−9).
Replacement of TFA with other acids such as triflic acid,
trichloroacetic acid, and methanesulfonic acid (MSA) in the
presence of Zn/CuI mixture was detrimental as the former two
acids did not favor cyclization (entries 10 and 11) at all,
whereas the MSA furnished 2a in diminished yield (entry 12).
Switching solvent from DMF to DMSO and acetonitrile
furnished products in reduced yield (entries 13 and 14).
Carrying out reactions under microwave conditions was found
to be ineffective (entries 15−17). Similarly, when replacing
CuI with other copper salts, Cu(OAc)2 (entry 18) was
inconclusive, and CuBr furnished 2a in 15% yield (entry 19).
Thus, the optimal conditions leading to the cyclization of 1a
required the combined presence of Zn dust (15 mol %)/CuI
(15 mol %)/TFA (0.1 equiv) in DMF. A careful survey of the
literature revealed Zn/CuI/TFA as a new catalytst system
hitherto not reported except for a Zn/CuI-mediated coupling
of akyl halides and vinyl sulfones via involvement of a possible
new Zn−Cu species.13
Mechanistically, formation of phenanthrenes 2 from
propargyl amines 1 may involve initial coordination of Zn/
Cu to the carbon−carbon triple bond to give complex A. This
may be then accompanied by the β-elimination of piperidine
via 1,5 hydride shift14 to form an allene intermediate 3, which
may subsequently undergo a 6π cycloaddition to form an
annulated tricyclic intermediate B. The latter may then
undergo isomerization to afford a phenanthrene derivative
based on 2 (Figure 1). Experimental evidence for the plausible
mechanism was established by synthesizing the allene inter-
mediate 3 by treating 1a with AgNO3 using literature
procedure.15 The resulting allene intermediate 3,4-dime-
thoxy-2′-[3-(4-tert-butyl-phenyl)propa-1,2-dienyl]-1,1′-bi-
phenyl 3a after its purification by column chromatography
was isolated in 65% yield. The allene 3a so obtained was then
subjected to intramolecular cyclization by exposing it to Zn/
CuI/TFA catalyst system to afford phenanthrene 2a within 1
h in quantitative yield (Scheme 1). Indeed, the allene
intermediate 3a was found to have poor shelf life stability,
which led us to work with a freshly isolated sample for its
characterization and cyclization.
Conversion of Propargyl Amine 1a to Phenanthrene 2a via
a
Carbocyclization
entry
solvent
catalyst(s)
CuI
acid
yield (%) 2a
1
DMF
DMF
DMF
toluene
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMSO
ACN
DMF
water
ACN
DMF
DMF
NR
NR
NR
NR
NR
2
3
Zn
4
ZnI2
5
Zn/CuI
Zn/CuI
c
6
TFA
TFA
TFA
TFA
94
7
NR
NR
NR
NR
NR
8
Zn
9
CuI
10
11
12
13
14
15
16
17
18
19
Zn/CuI
Zn/CuI
Zn/CuI
Zn/CuI
Zn/CuI
Zn/CuI/μW
Zn/CuI/μW
Zn/CuI/μW
triflic acid
trichloroacetic acid
MsOH
TFA
c
37
c
55
c
TFA
52
b
b
b
TFA
NR
NR
NR
NR
TFA
TFA
Zn/Cu(OAC)2
Zn/CuBr
TFA
d
TFA
15
a
All reactions were carried out on a 1 mmol scale, 15 mol % of each metal
catalyst, 0.1 equiv of acid, 1.5 mL of solvent, 12 h, 100 or 120 °C.
b
c
d
Microwave for 45 min. Isolated yield. Yield based on HPLC.
alone failed to furnish any product (entries 2−4). Similarly,
carrying out reaction in the presence of a mixture of Zn and
CuI yet again failed to facilitate cyclization (entry 5); however,
adding a catalytic amount of TFA to the mixture of Zn/CuI
furnished a tricyclic annulated 10-benzyl phenanthrene
derivative 2a after 12 h in 94% isolated yield (entry 6). Use
of TFA alone as a catalyst or in combination with Zn or CuI
Once the reaction conditions for the conversion of
propargylamine 1a to phenanthrene 2a were optimized, we
Figure 1. Plausible mechanism for the formation of phenanthrenes 2 from propargyl amines 1 (M represents Zn/Cu).
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one-pot three-component reaction involving formation of the
propargyl amine and subsequent carbocyclization proceeds via
a C(sp)-H activation−CH functionalization with imine-alkyne
activation−1,5 hydride shift−β-elimination of piperidine−
allene formation−6π cycloaddition−isomerization domino
sequence.
Scheme 1. Experimental Evidence for the Formation of 2a
via Allene Intermediate 3a
After optimizing the reaction conditions for the synthesis of
propargylamine 1a in quantitative yield, we proceeded with the
scope and limitation of the Zn/CuI/TFA catalyst system for
the one-pot synthesis of phenanthrenes (2) following a three-
component−carbocyclization domino reaction. Initially, we
treated 3′,4′-dimethoxy[1,1′-biphenyl]-2-carbaldehyde with
4-tert-butyl-phenylacetylene in the presence of a variety of
secondary amines, and the results are summarized in Table 3.
then embarked with the development of a three-component
strategy for the synthesis of propargylamine 1a. In the litera-
ture, metal-catalyzed formation of propargyl amines is known
to proceed via C(sp)-H activation of the alkyne followed by
functionalization with imines.16 Following this strategy, one of
the literature procedures8 involving Zn-catalyzed three-
component reaction furnished 1a in 52% isolated yield (entry
1, Table 2), which prompted us to improve its yield by treating
Table 3. Effect of Amines on the Synthesis of Phenanthrenes
(2) Using Domino Three-Component and Subsequent
Carbocyclization Reactions
Table 2. Optimization of Reaction Conditions for the
Synthesis of Propargyl Amine 1a in a Three-Component
a
Format
entry
secondary amines
yield (%) 2a
1
2
3
4
5
piperidine
92
68
56
58
63
diethylamine
diisopropylamine
morpholine
pyrrolidine
entry
reagents and conditions
yield (%) 1a
a
1
2
3
4
5
6
7
8
9
Zn dust, DMF, 120 °C, 12 h
Zn/CuI/TFA, DMF, 120 °C, 2 h
Zn dust, DMF, 120 °C, 2 h
Zn dust, CH3CN, Reflux, 2 h
CuI, DMF, 110 °C, 2 h
52
95
As is evident, piperidine furnished 2a in 92% isolated yields,
whereas DIPA, DEA, morpholine, and pyrrolidine furnished 2a
in reduced isolated yields of 56−68%.
traces
traces
>10
In subsequent studies, we treated a series of biphenyl-2-
carbaldehydes with terminal alkynes and piperidine in the
presence of the Zn/CuI/TFA catalyst system to generate
corresponding propargyl amines in three-component format
followed by in situ elimination of piperidine and intramolecular
cyclization to furnish 9/10-substituted phenanthrenes 2a−r
(Table 4). The crude products were purified by column
chromatography. Substitution in the B ring of biphenyl-2-
carbaldehyde in the form of 3′,4′-dimethoxy and 3′,4′,5′-
trimethoxy as R2 had no effect on the outcome of the reaction
when treated with phenylacetylene/piperdine, furnishing
corresponding phenanthrene derivatives 2b and 2f in the
isolated yield of 90% and 79%, respectively. Similarly,
substitution in the A ring of the biphenyl-2-carbaldehyde in
the form 6-ethoxy and 3,4-dimethoxy groups as R1 had no
effect on the yield when treated with aromatic terminal
alkynes/piperdine except that the reaction was found to be
sluggish and required addition of fresh Zn/CuI/TFA catalyst
system after 10 h to drive the reaction to completion (2i−2l;
81−87% and 2m−2o; 77−82%). Among aromatic terminal
alkynes, the electronic effect in the phenyl ring represented by
R3 had negligible effect on the reactions, offering products with
minimal variation in yields. An attempt to employ aliphatic
alkynes failed to furnish phenanthrene from the corresponding
propargylamine intermediate formed in situ.
TFA, DMF, 110 °C, 2 h
NR
Zn/CuI, DMF, 120 °C, 2 h
CuI/TFA, DMF, 120 °C, 2 h
Zn/TFA, DMF, 120 °C, 2 h
traces
traces
traces
a
All reactions were carried out on a 1 mmol scale with aldehyde/
amine/alkyne = 1:1.5:1.2, 15 mol % of each metal catalyst, 0.1 equiv of
acid, 1.5 mL of DMF. Reference 7.
a
3′,4′-dimethoxy[1,1′-biphenyl]-2-carbaldehyde with 4-tert-butyl-
phenylacetylene and piperidine in a MCR format by employing
the same Zn/CuI/TFA catalyst system identified above for the
carbocyclization. Using the same catalyst system for both steps
may facilitate development of a one-pot strategy for phenan-
threnes following a domino three-component−carbocyclization
reaction. Pleasingly, the three-component reaction using Zn/
CuI/TFA catalyst system afforded propargyl amine 1a within
2 h in 95% isolated yield (entry 2, Table 2).
Notably, we did not observe any subsequent formation of 2a
from 1a in the presence of the Zn/CuI/TFA catalyst system in
the first 2 h of the reaction. It is thus evident that, using the Zn/
CuI/TFA catalyst system, although formation of the 1a seemed
to occur smoothly (2 h), longer duration (12 h) was required
for its post-MCR conversion to 2a. Attempts to carry out the
reaction in the presence of Zn, CuI, and TFA alone or as a
metal−acid combination furnished propargylamine 1a in traces
(<10%) as evident by HPLC (entries 3−9, Table 2). Thus, the
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a
Table 4. Synthesis of Phenanthrenes (2) Using Domino Three-Component and Subsequent Carbocyclization Reactions
a
All reactions were carried out on a 1 mmol scale with aldehyde/amine/alkyne = 1:1.5:1.2, 15 mol % of each metal catalyst, 0.1 equiv of acid, 1.5 mL
of solvent.
(t), quartet (q), multiplet (m). High resolution mass spectra were
recorded with a mass spectrometer. Column chromatography was
CONCLUSION
■
In summary, we have developed a one-pot atom-economical
construction of polycyclic 9/10-substituted-phenanthrenes via
performed using silica gel (100−200 mesh) as the stationary phase. All
reactions were monitored by thin layer chromatography (TLC). The
Zn/CuI/TFA-catalyzed domino three-component and subse-
purity and characterization of these compounds were further
quent carbocyclization reactions. The protocol may find
application in the diversity oriented synthesis of chemprobes
with structural complexity.
established using HR/EI Mass spectroscopy. Melting points were
measured on a capillary melting point apparatus and are uncorrected.
II. General Procedure for the Synthesis of Biphenyl-2-
carbaldehyde via Suzuki Coupling. A solution of phenylboronic
acid (1.4 g, 11.89 mmol) and 2-bromobenzaldehyde (2.0 g, 10.81
mmol) in DMF (10 mL) was degassed with nitrogen for 15 min
followed by addition of Na2CO3 (5.8 g, 2 M in water) under conti-
nuous flow of nitrogen. Pd(PPh3)4 (1.25 g, 1.08 mmol) was added to
the reaction mixture under a nitrogen atmosphere. The reaction
mixture was stirred at 80 °C for 3 h. The solution was diluted with
H2O (5 mL), and then the product was extracted three times with
EtOAc (10 mL). The combined organic layer was dried over Na2SO4,
and the solvent was removed in vacuo. The crude product was purified
EXPERIMENTAL SECTION
■
I. General Information and Methods. All reagents and solvents
were purchased from commercial sources and used without
purification. NMR spectra were recorded with 200 and 300 MHz
spectrometers for 1H NMR and 50 and 75 MHz for 13C NMR.
Chemical shifts δ are given in ppm relative to the residual signals of
tetramethylsilane in CDCl3 or deuterated solvent CDCl3/DMSO-d6
for 1H and 13C NMR. Multiplicities are reported as follows: singlet (s),
doublet (d), doublet of doublets (dd), doublet of triplets (dt), triplet
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on a silica gel column using hexane/ethyl acetate (95:5, v/v) as eluent
to afford biphenyl-2-carbaldehyde in 81% yield.
3,4-Dimethoxy-2′-[3-(4-tert-butyl-phenyl)propa-1,2-dienyl]-1,1′-
biphenyl (3a). Yield = 65%, yellow oil, Rf = 0.61 (1:19 EtOAc/
hexane); IR (Neat) νmax 3206, 2950, 1723, 1514 cm−1; 1H NMR (300
MHz, CDCl3) δ 7.57−7.54 (m, 1H), 7.35−7.24 (m, 7H), 6.98−6.92
(m, 3H), 6.66 (d, J = 6.5 Hz, 1H), 6.52 (d, J = 6.4 Hz, 1H), 3.93 (s,
3H), 3.91 (s, 3H), 1.31 (s, 9H); 13C NMR (75 MHz, CDCl3) δ 208.3,
150.5, 148.7, 148.5, 140.4, 133.7, 131.5, 130.9, 130.4, 127.7, 127.5,
127.2, 126.7, 125.8, 122.2, 113.3, 111.1, 97.8, 96.7, 56.0, 34.7, 31.4
ppm; HRMS (ESI) calcd for C27H29O2 [M + H] 385.2167 found
385.2170.
3′,4′-Dimethoxy[1,1′-biphenyl]-2-carbaldehyde. Yield = 85%,
white solid, mp 90−93 °C, Rf = 0.16 (1:19 EtOAc/hexane); IR
1
(KBr) νmax 3012, 2937, 1688 cm−1; H NMR (300 MHz, CDCl3) δ
10.00 (s, 1H), 8.00 (d, J = 7.9 Hz, 1H), 7.65−7.60 (m, 1H), 7.47 (t,
J = 7.9 Hz, 2H), 6.98−6.90 (m, 3H), 3.95 (s, 3H), 3.91 (s, 3H); 13C
NMR (75 MHz, CDCl3) δ 192.6, 149.3, 148.9, 145.8, 133.9, 133.5,
130.7, 130.4, 127.6, 127.5, 122.9, 113.2, 111.1, 56.0 ppm; HRMS (ESI)
calcd for C15H15O3 [M + H] 243.1021 found 243.1019.
V. Procedure for the Synthesis of Phenanthrene (2a) from
Allene (3a). To a solution of allene 3a (1.0 mmol) in DMF were
added Zn (15 mol %), CuI (15 mol %), and TFA (0.1 mmol) at room
temperature. The reaction mixture was heated at 120 °C for 1 h. After
completion of reaction, NaHCO3 soltion was added, and the product
was extracted three times with EtOAc (5 mL). The combined organic
layer was dried over Na2SO4, and the solvent was removed in vacuo.
The crude product was purified on a silica gel column using hexane/
ethyl acetate as eluent to afford phenanthrene 2a.
2,3-dimethoxy-10-(4-(tert-butyl)benzyl)phenanthrene (2a). Yield =
92%, white solid, mp 132−135 °C, Rf 1= 0.32 (1:19 EtOAc/hexane); IR
(KBr) νmax 2958, 1622, 1219 cm−1; H NMR (300 MHz, CDCl3) δ
8.50 (d, J = 7.44 Hz, 1H), 8.02 (s, 1H), 7.82 (d, J = 6.93 Hz, 1H),
7.60−7.48 (m, 3H), 7.33−7.17 (m, 5H), 4.40 (s, 2H), 4.08 (s, 3H),
3.84 (s, 3H), 1.28 (s, 9H).; 13C NMR (75 MHz, CDCl3) δ 149.2,
149.1, 148.9, 137.5, 134.4, 131.4, 129.5, 128.5, 128.4, 126.6, 126.4,
125.9, 125.7, 125.5, 122.1, 106.0, 103.8, 56.0, 55.8, 39.9, 34.5, 31.5
ppm; HRMS (ESI) calcd for C27H29O2 [M + H] 385.2167 found
385.2152.
VI. General Procedure for the Synthesis of Phenanthrenes.
To a solution of biphenyl-2-carbaldehyde (1.0 mmol), piperidine
(1.5 mmol), and phenyl acetylene (1.2 mmol) in DMF were added Zn
(15 mol %), CuI (15 mol %), and TFA (0.1 mmol) at room
temperature. The reaction mixture was heated at 120 °C for 12−14 h.
After completion of reaction, NaHCO3 solution was added, and the
product was extracted three times with EtOAc (5 mL). The combined
organic layer was dried over Na2SO4, and the solvent was removed in
vacuo. The crude product was purified on a silica gel column using
hexane/ethyl acetate as eluent to afford phenanthrenes.
3′,4′,5′-Trimethoxy[1,1′-biphenyl]-2-carbaldehyde. Yield = 77%,
white solid, mp 102−106 °C, Rf = 0.34 (1:19 EtOAc/hexane); IR
1
(KBr) νmax 3370, 2930, 2847, 1695, 1587 cm−1; H NMR (300 MHz,
CDCl3) δ 10.01 (s, 1H), 8.01 (dd, J1 = 0.93 Hz, J2 = 7.65 Hz, 1H),
7.66−7.60 (m, 1H), 7.52−7.45 (m, 2H), 6.57 (s, 2H), 3.92 (s, 3H),
3.88 (s, 6H); 13C NMR (75 MHz, CDCl3) δ 192.5, 153.1, 146.0,
138.0, 133.9, 133.5, 133.4, 130.5, 127.8, 127.5, 107.5, 61.0, 56.3 ppm;
HRMS (ESI) calcd for C16H17O4 [M + H] 273.1127 found 273.1117.
6-Ethoxy-3′,4′-dimethoxy[1,1′-biphenyl]-2-carbaldehyde. Yield =
65%, white solid, mp 116−118 °C, Rf = 0.20 (1:19 EtOAc/hexane);
1
IR (KBr) νmax 3360, 2939, 2823, 1675,1573 cm−1; H NMR (300
MHz, CDCl3) δ 9.77 (s, 1H), 7.63−7.57 (m, 1H), 7.43−7.37 (m, 1H),
7.21−7.15 (m, 1H), 6.95−6.92 (m, 2H), 6.82 (dd, J1 = 1.2 Hz, J2 = 8.2
Hz, 1H), 4.03 (q, J = 6.9 Hz, 2H), 3.94 (s, 3H), 3.88 (s, 3H), 1.30 (t,
J = 6.9 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 192.9, 156.5, 148.8,
148.3, 135.8, 134.9, 128.5, 125.6, 124.3, 119.2, 117.3, 114.4, 110.5,
64.6, 56.0, 14.8 ppm; HRMS (ESI) calcd for C17H19O4 [M + H]
287.1283 found 287.1283.
[1,1′-Biphenyl]-2-carbaldehyde.17a Yield = 81%, yellow liquid,
R
= 0.15 (1:19 EtOAc/hexane); IR (Neat) νmax 3063, 2851, 1690
f
1
cm−1; H NMR (300 MHz, CDCl3) δ 10.01 (s, 1H), 8.06 (dd, J1 =
0.63 Hz, J2 = 7.74 Hz, 1H), 7.69−7.63 (m, 1H), 7.54−7.46 (m, 5H),
7.42−7.39 (m, 2H); 13C NMR (75 MHz, CDCl3) δ 192.5, 146.0,
137.8, 133.8, 133.6, 130.9, 130.2, 128.5, 128.2, 127.8, 127.7 ppm;
HRMS (ESI) calcd for C13H11O [M + H] 183.0809 found 183.0820.
4,5-Dimethoxy[1,1′-biphenyl]-2-carbaldehyde.17b Yield = 73%,
white solid, mp 124−126 °C, Rf = 0.21 (1:19 EtOAc/hexane); IR
(KBr) νmax 3022, 2925, 1673 cm−1; 1H NMR (300 MHz, CDCl3) δ =
9.82 (s, 1H), 7.54 (s, 1H), 7.49−7.41 (m, 3H), 7.39−7.36 (m, 2H),
6.86 (s, 1H), 3.98 (s, 3H), 3.97 (s, 3H); 13C NMR (50 MHz, CDCl3)
δ 191.1, 153.5, 148.8, 141.5, 137.6, 130.2, 128.4, 128.0, 127.0, 121.7,
108.7, 56.2, 56.1 ppm; HRMS (ESI) calcd for C15H15O3 [M + H]
243.1021 found 243. 1019.
10-Benzyl-2,3-dimethoxyphenanthrene (2b). Yield = 90%, white
solid, mp 174−177 °C, Rf = 0.60 (1:19 EtOAc/hexane); IR (KBr) νmax
1
3026, 2911, 1440 cm−1; H NMR (300 MHz, CDCl3) δ 8.51 (d, J =
8.0 Hz, 1H), 8.03 (s, 1H), 7.83−7.80 (m, 1H), 7.61−7.49 (m, 3H),
7.31−7.17 (m, 6H), 4.44 (s, 2H), 4.09 (s, 3H), 3.85 (s, 3H); 13C NMR
(75 MHz, CDCl3) δ 149.1, 148.9, 140.5, 134.2, 131.4, 129.5, 128.8,
128.5, 126.5, 126.5, 126.3, 125.9, 125.8, 125.7, 122.1, 105.9, 103.8,
56.0, 55.8, 40.5 ppm; HRMS (ESI) calcd for C23H21O2 [M + H]
329.1541 found 329.1533.
III. Procedure for the Synthesis of 3-Ethoxy-2-trifluoro-
methanesulfonylmethyl-benzaldehyde. To a stirred solution of
3-ethoxy-2-hydroxy-benzaldehyde (5.0 g, 30.12 mmol) and triethyl-
amine (4.70 mL, 33.13 mmol) in DCM (20 mL) at 0 °C was added
triflic anhydride (5.56 mL, 33.13 mmol). The reaction mixture was
stirred at 0 °C for 1 h and at room temperature for 2 h. After
completion of reaction, NaHCO3 solution was added, and the product
was extracted three times with DCM (10 mL). The combined organic
layer was dried over Na2SO4, and the solvent was removed in vacuo.
The crude product was subjected to Suzuki coupling using the above-
described procedure.
2,3-Dimethoxy-10-(4-methoxybenzyl)phenanthrene (2c). Yield =
79%, white solid, mp 122−125 °C, Rf = 0.17 (1:19 EtOAc/hexane); IR
(KBr) νmax 3006, 2959, 1611, 1508 cm−1; 1H NMR (300 MHz,
CDCl3) δ 8.50 (d, J = 8.0 Hz, 1H), 8.02 (s, 1H), 7.81−7.79 (m, 1H),
7.60−7.48 (m, 3H), 7.32 (s, 1H), 7.16 (d, J = 8.6 Hz, 2H), 6.81 (d, J =
8.6 Hz, 2H), 4.37 (s, 2H), 4.08 (s, 3H), 3.87 (s, 3H), 3.76 (s, 3H); 13
C
NMR (75 MHz, CDCl3) δ 158.1, 149.1, 148.9, 134.5, 132.4, 131.4,
129.7, 129.5, 128.5, 126.5, 126.2, 125.9, 125.7, 125.6, 122.1, 114.0,
105.7, 103.8, 56.0, 55.8, 55.3, 39.5 ppm; HRMS (ESI) calcd for
C24H23O3 [M + H] 359.1647 found 359.1641.
3-Ethoxy-2-trifluoromethanesulfonylmethyl-benzaldehyde. Yield =
81%, white liquid, Rf = 0.61 (1:19 EtOAc/hexane); IR (Neat) νmax
1
3460, 2152, 1700, cm−1; H NMR (300 MHz, CDCl3) δ 10.24 (s,
1H), 7.52−7.49 (m, 1H), 7.46−7.41 (m, 1H), 7.30−7.26 (m, 1H),
4.18 (q, J = 6.9 Hz, 2H), 1.50 (t, J = 6.9 Hz, 3H); 13C NMR (75 MHz,
CDCl3) δ 186.8, 151.0, 139.0, 129.5, 129.0, 121.0, 119.3, 65.4, 14.0
ppm; HRMS (ESI) calcd for C10H10F3O5S [M + H] 299.0201 found
299.0203.
IV. Procedure for the Synthesis of 3,4-Dimethoxy-2′-[3-(4-
tert-butyl-phenyl)propa-1,2-dienyl]-1,1′-biphenyl 3a. To a solu-
tion of 1a (1.0 mmol) in CH3CN was added AgNO3 (0.5 mmol) at
room temperature. The reaction mixture was stirred at room
temperature for 48 h in the absence of light. After the completion
of the reaction, the solvent was removed in vacuo. The crude product
was purified on a silica gel column using hexane/ethyl acetate as eluent
to afford allene (3a).
2,3-Dimethoxy-10-(4-methylbenzyl)phenanthrene (2d). Yield =
89%, white solid, mp 148−152 °C, Rf 1= 0.38 (1:19 EtOAc/hexane); IR
(KBr) νmax 3011, 2916, 1437 cm−1; H NMR (300 MHz, CDCl3) δ
8.51 (d, J = 8.0 Hz, 1H), 8.03 (s, 1H), 7.82 (d, J = 7.5 Hz, 1H), 7.61−
7.49 (m, 3H), 7.35 (s, 1H), 7.16 (d, J = 7.9 Hz, 2H), 7.08 (d, J = 7.9
Hz, 2H), 4.40 (s, 2H), 4.09 (s, 3H), 3.87 (s, 3H), 2.31 (s, 3H); 13C
NMR (75 MHz, CDCl3) δ 149.1, 148.9, 137.4, 135.8, 134.5, 131.4,
129.5, 129.3, 128.7, 128.5, 126.5, 126.3, 125.9, 125.7, 125.7, 122.1,
105.8, 103.8, 56.0, 55.8, 40.0, 21.1 ppm; HRMS (ESI) calcd for
C24H23O2 [M + H] 343.1698 found 343.1688.
1,2,3-Trimethoxy-10-(4-(tert-butyl)benzyl)phenanthrene (2e). Yield =
79%, yellow oil, Rf = 0.44 (1:19 EtOAc/hexane); IR (Neat) νmax 3439,
10126
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1
3172, 2958, 1656 cm−1; H NMR (300 MHz, CDCl3) δ 8.50 (d, J =
2,3-Dimethoxy-5-ethoxy-10-(4-methylbenzyl)phenanthrene
(2l). Yield = 84%, white solid, mp 128−132 °C, Rf = 0.25 (1:19
EtOAc/hexane); IR (KBr) νmax 3172, 2958, 1656 cm−1; 1H NMR (300
MHz, CDCl3) δ 9.41 (s, 1H), 7.48 (s, 1H), 7.43−7.39 (m, 2H), 7.34
(s, 1H), 7.13 (d, J = 7.8 Hz, 2H), 7.06−7.04 (m, 3H), 4.38 (s, 2H),
4.37 (q, J = 6.8 Hz, 2H), 4.05 (s, 3H), 3.85 (s, 3H), 2.29 (s, 3H), 1.68
(t, J = 6.8 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 157.3, 147.8, 137.4,
135.7, 134.8, 133.9, 129.3, 128.7, 127.3, 126.9, 125.9, 125.6, 121.4,
120.1, 110.3, 108.1, 105.3, 64.4, 55.8, 55.6, 40.0, 21.1, 15.5 ppm;
HRMS (ESI) calcd for C26H27O3 [M + H] 387.1960 found 387.1947.
2,3-Dimethoxy-9-(4-(tert-butyl)benzyl)phenanthrene (2m). Yield =
77%, white solid, mp 130−135 °C, Rf = 0.61 (1:19 EtOAc/hexane); IR
(KBr) νmax 3012, 2958, 1622, 1219 cm−1; 1H NMR (300 MHz,
CDCl3) δ 8.56 (d, J = 8.1 Hz, 1H), 8.04 (d, J = 8.1 Hz, 1H), 7.99 (s,
1H), 7.59 (t, J = 7.7 Hz, 1H), 7.50 (d, J = 8.0 Hz, 1H), 7.46 (s, 1H),
7.30−7.24 (m, 2H), 7.18 (d, J = 5.8 Hz, 3H), 4.43 (s, 2H), 4.10 (s,
3H), 4.01 (s, 3H), 1.29 (s, 9H); 13C NMR (75 MHz, CDCl3) δ 149.5,
149.2, 149.0, 137.5, 133.4, 130.8, 130.4, 128.5, 127.0, 127.0, 125.9,
125.7, 125.5, 125.3, 124.5, 122.7, 108.3, 103.4, 56.1, 56.0, 39.0, 34.5,
31.5 ppm; HRMS (ESI) calcd for C27H29O2 [M + H] 385.2167 found
385.2150.
7.9 Hz, 1H), 7.92 (s, 1H), 7.72 (d, J = 6.4 Hz, 1H), 7.58−7.48
(m, 2H), 7.33 (s, 1H), 7.28−7.25 (m, 2H), 7.15−7.09 (m, 2H), 4.66
(s, 2H), 4.08 (s, 3H), 3.92 (s, 3H), 3.67(s, 3H), 1.28 (s, 9H); 13C
NMR (75 MHz, CDCl3) δ 152.6, 151.7, 148.4, 142.4, 139.3, 134.4,
131.8, 129.0, 128.7, 128.4, 128.2, 126.5, 126.0, 125.1, 122.5, 121.6,
100.0, 61.3, 60.9, 56.0, 42.0, 34.4, 31.6 ppm; HRMS (ESI) calcd for
C28H31O3 [M + H] 415.2273 found 415.2261.
10-Benzyl-1,2,3-trimethoxyphenanthrene (2f). Yield = 79%,
yellow oil, Rf = 0.44 (1:19 EtOAc/hexane); IR (Neat) νmax 3329,
1
2930, 2947, 1657 cm−1; H NMR (300 MHz, CDCl3) δ 8.50 (d, J =
8.0 Hz, 1H), 7.92 (s, 1H), 7.73−7.70 (m, 1H), 7.56−7.50 (m, 2H),
7.33 (s, 1H), 7.27−7.23 (m, 2H), 7.22−7.15 (m, 3H), 4.69 (s, 2H),
4.08 (s, 3H), 3.91 (s, 3H), 3.65 (s, 3H); 13C NMR (75 MHz, CDCl3)
δ 152.6, 151.7, 142.4, 134.0, 131.7, 129.1, 128.8, 128.7, 128.6, 128.3,
128.2, 126.5, 126.1, 125.6, 122.6, 121.6, 100.0, 61.3, 60.9, 56.0, 42.6
ppm; HRMS (ESI) calcd for C24H23O3 [M + H] 359.1647 found
359.1648.
1,2,3-Trimethoxy-10-(4-methoxybenzyl)phenanthrene (2g). Yield =
81%, yellow oil, Rf = 0.28 (1:19 EtOAc/hexane); IR (Neat) ν max 3417,
1
3152, 2938, 1456 cm−1; H NMR (300 MHz, CDCl3) δ 8.50 (d, J =
9-Benzyl-2,3-dimethoxyphenanthrene (2n). Yield = 82%, white
7.8 Hz, 1H), 7.91 (s, 1H), 7.71 (d, J = 7.5 Hz, 1H), 7.57−7.47 (m,
solid, mp 144−146 °C, Rf = 0.38 (1:19 EtOAc/hexane); IR (KBr) νmax
2H), 7.30 (s, 1H), 7.08 (d, J = 8.1 Hz, 2H), 6.80 (d, J = 7.9 Hz, 2H),
1
3033, 2925, 1430 cm−1; H NMR (300 MHz, CDCl3) δ 8.56 (d, J =
4.62 (s, 2H), 4.07 (s, 3H), 3.92 (s, 3H), 3.76 (s, 3H), 3.70 (s, 3H); 13
C
8.3 Hz, 1H), 8.02 (s, 1H), 7.99 (s, 1H), 7.59 (t, J = 7.0 Hz, 1H), 7.48
(t, J = 7.7 Hz, 1H), 7.43 (s, 1H), 7.28−7.20 (m, 5H), 7.16 (s, 1H),
4.46 (s, 2H), 4.10 (s, 3H), 4.01 (s, 3H); 13C NMR (75 MHz, CDCl3)
δ 149.5, 149.2, 140.6, 133.2, 130.6, 130.4, 128.9, 128.5, 127.0, 127.0,
126.2, 125.9, 125.7, 125.1, 124.4, 122.7, 108.2, 103.4, 56.1, 55.9, 39.5
ppm; HRMS (ESI) calcd for C23H21O2 [M + H] 329.1541 found
329.1538.
NMR (75 MHz, CDCl3) δ 157.7, 152.6, 151.7, 142.5, 134.6, 134.4,
131.7, 130.4, 129.7, 129.0, 128.7, 128.3, 128.2, 126.5, 126.0, 122.5,
121.6, 113.7, 100.0, 61.4, 60.9, 56.0, 55.3, 41.6 ppm; HRMS (ESI)
calcd for C25H25O4 [M + H] 389.1753 found 389.1749.
1,2,3-Trimethoxy-10-(4-methylbenzyl)phenanthrene (2h). Yield =
76%, yellow oil, Rf = 0.43 (1:19 EtOAc/hexane); IR (Neat) ν
max
3420, 2958, 1650, 1447 cm−1; 1H NMR (300 MHz, CDCl3) δ 8.50 (d,
J = 7.7 Hz, 1H), 7.92 (s, 1H), 7.72 (d, J = 6.2 Hz, 1H), 7.58−7.48 (m,
2H), 7.32 (s, 1H), 7.06 (m, 4H), 4.65 (s, 2H), 4.09 (s, 3H), 3.92 (s,
3H), 3.68 (s, 3H), 2.30 (s, 3H); 13C NMR (75 MHz, CDCl 3) δ 152.6,
151.7, 142.4, 139.2, 135.0, 134.4, 131.7, 129.0, 128.9, 128.7, 128.6,
128.4, 128.2, 126.4, 126.0, 122.5, 121.6, 100.0, 61.3, 60.9, 56.0, 42.0,
21.1 ppm; HRMS (ESI) calcd for C25H25O3 [M + H] 373.1803 found
373.1798.
2,3-Dimethoxy-9-(4-methylbenzyl)phenanthrene (2o). Yield =
81%, white solid, mp 108−110 °C, Rf = 0.36 (1:19 EtOAc/hexane);
1
IR (KBr) νmax 3021, 2923, 1440 cm−1; H NMR (300 MHz, CDCl3)
δ = 8.56 (d, J = 7.9 Hz, 1H), 8.03−7.99 (m, 2H), 7.59 (t, J = 7.5 Hz,
1H), 7.49 (t, J = 8.2 Hz, 1H), 7.43 (s, 1H), 7.16−7.07 (m, 5H), 4.42
(s, 2H), 4.11 (s, 3H), 4.01 (s, 3H), 2.31 (s, 3H); 13C NMR (75 MHz,
CDCl3) δ 149.5, 149.2, 137.5, 135.6, 133.5, 130.7, 130.4, 129.3, 128.8,
127.0, 126.9, 125.9, 125.7, 125.2, 124.4, 122.7, 108.2, 103.4, 56.1, 56.0,
39.1, 21.1 ppm; HRMS (ESI) calcd for C24H23O2 [M + H] 343.1698
found 343.1690.
2,3-Dimethoxy-5-ethoxy-10-(4-(tert-butyl)benzyl)phenanthrene
(2i). Yield = 87%, white solid, mp 139−141 °C, Rf = 0.26 (1:19
EtOAc/hexane); IR (KBr) νmax 3439, 2363, 1630 cm−1; 1H NMR (300
MHz, CDCl3) δ 9.42 (s, 1H), 7.51 (s, 1H), 7.44−7.42 (m, 2H), 7.35
(s, 1H), 7.28 (s, 1H), 7.17 (d, J = 8.2 Hz, 3H), 7.05 (dd, J1 = 2.7 Hz,
J2 = 6.5 Hz, 1H), 4.40 (s, 2H), 4.31 (q, J = 7.1 Hz, 2H), 4.05 (s, 3H),
3.84 (s, 3H), 1.69 (t, J = 6.9 Hz, 3H), 1.27 (s, 9H); 13C NMR (75
MHz, CDCl3) δ 157.3, 149.0, 147.8, 137.5, 134.8, 133.9, 128.4, 127.3,
126.9, 126.0, 125.6, 125.4, 121.4, 120.1, 114.2, 110.3, 108.1, 105.5,
64.4, 55.8, 55.6, 40.0, 34.5, 31.5, 15.5 ppm; HRMS (ESI) calcd for
C29H33O3 [M + H] 429.2429 found 429.2428.
10-Benzyl-2,3-dimethoxy-5-ethoxyphenanthrene (2j). Yield =
85%, white solid, mp 133−136 °C, Rf = 0.25 (1:19 EtOAc/hexane);
IR (KBr) νmax 3444, 2841, 1650 cm−1; 1H NMR (300 MHz, CDCl3) δ
9.42 (s, 1H), 7.49 (s, 1H), 7.44−7.42 (m, 2H), 7.32 (s, 1H), 7.25−
7.17 (m, 5H), 7.07−7.04 (m, 1H), 4.43 (s, 2H), 4.31 (q, J = 6.9 Hz,
2H), 4.05 (s, 3H), 3.83 (s, 3H), 1.68 (t, J = 6.8 Hz, 3H); 13C NMR
(75 MHz, CDCl3) δ 157.3, 147.8, 140.5, 139.4, 134.5, 133.9, 128.8,
128.6, 127.2, 127.0, 126.3. 126.0, 125.7, 121.4, 120.1, 114.2, 110.3,
108.2, 105.3, 64.4, 55.8, 55.6, 40.5, 15.5 ppm; HRMS (ESI) calcd for
C25H25O3 [M + H] 373.1803 found 373.1803.
9-[4-(tert-Butyl)benzyl]phenanthrene (2p). Yield = 77%, white
solid, mp 132−135 °C, Rf = 0.90 (1:19 EtOAc/hexane); IR (KBr) νmax
1
2927, 2860, 1649 cm−1; H NMR (300 MHz, CDCl3) δ 8.76 (d, J =
8.4 Hz, 1H), 8.69 (d, J = 7.5 Hz, 1H), 8.09 (d, J = 7.6 Hz, 1H), 7.84
(d, J = 7.5 Hz, 1H), 7.68−7.59 (m, 5H), 7.32 (d, J = 7.9 Hz, 2H), 7.20
(d, J = 8.0 Hz, 2H), 4.49 (s, 2H), 1.32 (s, 9H); 13C NMR (75 MHz,
CDCl3) δ 149.0, 137.3, 135.1, 132.0, 131.6, 130.9, 130.1, 128.5, 128.4,
127.9, 126.7, 126.3, 126.3, 125.5, 125.2, 123.2, 122.6, 39.2, 34.5, 31.5
ppm; HRMS (ESI) calcd for C25H25 [M + H] 325.1956 found
325.1926.
9-Benzylphenanthrene (2q). Yield = 83%, white solid, mp 142−
145 °C, Rf = 0.92 (1:19 EtOAc/hexane); IR (KBr) νmax 3027, 2913,
1
1596 cm−1; H NMR (300 MHz, CDCl3) δ 8.77 (d, J = 8.1 Hz, 1H),
8.71 (d, J = 8.0 Hz, 1H), 8.07 (d, J = 8.0 Hz, 1H), 7.87−7.84 (m, 1H),
7.69−7.56 (m, 5H), 7.37−7.23 (m, 5H), 4.53 (s, 2H); 13C NMR (75
MHz, CDCl3), δ 140.3, 134.8, 131.9, 131.5, 130.9, 130.0, 128.9, 128.6,
128.3, 128.0, 126.7, 126.7, 126.3, 126.2, 125.1, 123.2, 122.6, 39.7 ppm;
HRMS (ESI) calcd for C21H17 [M + H] 269.1330 found 269.1333.
9-(4-Methylbenzyl)phenanthrene (2r). Yield = 74%, white solid,
mp 120−123 °C, Rf = 0.87 (1:19 EtOAc/hexane); IR (KBr) νmax 3022,
2923, 1660 cm−1; 1H NMR (300 MHz, CDCl3) δ 8.72 (d, J = 8.1 Hz,
1H), 8.65 (d, J = 7.9 Hz, 1H), 8.03 (d, J = 8.0 Hz, 1H), 7.80 (d, J = 7.3
Hz, 1H), 7.63−7.53 (m, 5H), 7.13 (d, J = 7.5 Hz, 2H), 7.07 (d, J = 7.7
Hz, 2H), 4.44 (s, 2H), 2.30 (s, 3H); 13C NMR (75 MHz, CDCl3) δ
137.3, 135.7, 135.2, 131.9, 131.6, 130.9, 130.1, 129.3, 128.8, 128.4,
127.9, 126.7, 126.7, 126.3, 126.3, 125.2, 123.2, 122.6, 39.3, 21.1 ppm;
DART-HRMS (ESI) calcd for C22H19 [M+] 282.1408 found 282.1406.
3′,4′-Dimethoxy-1-(biphenyl-2-yl)-3-(cyclohex-1-en-1-yl) piperi-
2,3-Dimethoxy-5-ethoxy-10-(4-methoxybenzyl)phenanthrene
(2k). Yield = 81%, white solid, mp 136−138 °C, Rf = 0.92 (1:19
EtOAc/hexane); IR (KBr) νmax 3016, 2963, 1623, 1512 cm−1; 1H
NMR (300 MHz, CDCl3) δ 9.42 (s, 1H), 7.47 (s, 1H), 7.43−7.39 (m,
2H), 7.34 (s, 1H), 7.16 (d, J = 8.5 Hz, 2H), 7.05 (dd, J1 = 3.6 Hz, J2 =
5.5 Hz, 1H), 6.80 (d, J = 8.6 Hz, 2H), 4.37 (s, 2H), 4.31 (q, J = 7.0 Hz,
2H), 4.06 (s, 3H), 3.86 (s, 3H), 3.76 (s, 3H), 1.69 (t, J = 6.8 Hz, 3H);
13C NMR (75 MHz, CDCl3) δ 158.1, 157.3, 147.8, 134.9, 133.9, 132.5,
129.7, 127.2, 126.8, 125.9, 125.6, 121.4, 120.0, 114.0, 110.3, 108.1,
105.2, 64.3, 55.8, 55.6, 55.3, 39.6, 15.5 ppm; HRMS (ESI) calcd for
C26H27O4 [M + H] 403.1909 found 403.1900.
dine. Yield = 93%, yellow oil, R = 0.16 (1:19 EtOAc/hexane); IR
f
10127
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Article
(Neat) νmax 3404, 2932, 2368, 1592 cm−1; 1H NMR (300 MHz,
CDCl3) δ 7.72−7.69 (m, 1H), 7.33−7.29 (m, 2H), 7.23 (s, 1H),
7.09−7.05 (m, 2H), 6.89 (d, J = 8.1 Hz, 1H), 6.08 (s, 1H), 4.53 (s,
1H), 3.92 (s, 3H), 3.89 (s, 3H), 2.51−2.49 (m, 2H), 2.31−2.27 (m,
K.; Gupta, S.; Saifuddin, M.; Mandadapu, A. K.; Agarwal, P. K.;
Gauniyal, H. M.; Kundu, B. Tetrahedron Lett. 2011, 5, 65. (d) Sharma,
S. K.; Mandadapu, A. K.; Saifuddin, M.; Gupta, S.; Agarwal, P. K.;
Mandwal, A. K.; Gauniyal, H. M.; Kundu, B. Tetrahedron Lett. 2010,
51, 6022. (e) Saha, B.; Sharma, S.; Sawant, D.; Kundu, B. Synlett 2007,
1591. (f) Saha, B.; Kumar, R.; Maulik, P. R.; Kundu, B. Tetrahedron
Lett. 2006, 47, 2765.
2H), 2.14−2.07 (m, 4H), 1.61−1.57 (m, 7H), 1.48−1.45 (m, 3H); 13
C
NMR (75 MHz, CDCl3) δ 148.2, 148.2, 142.4, 137.1, 134.2, 134.0,
130.4, 129.7, 127.3, 126.6, 122.1, 120.8, 113.5, 110.6, 89.3, 84.2, 59.2,
56.0, 56.0, 50.3, 29.7, 26.4, 25.6, 24.6, 22.4, 21.6 ppm; HRMS (ESI)
calcd for C28H34NO2 [M + H] 416.2589 found 416.2571.
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Venkanna, G. T. Tetrahedron Lett. 2007, 48, 7332.
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2-ynyl)-piperidine (1a). Yield = 95%, yellow oil, Rf = 0.16 (1:19
1
EtOAc/hexane); IR (Neat) ν
3464, 2938, 2367, 1513 cm−1; H
max
NMR (300 MHz, CDCl3) δ 7.80 (s, 1H), 7.40−7.35 (m, 2H), 7.33−
7.31 (m, 4H), 7.30−7.29 (m, 1H), 7.10 (d, J = 9.4 Hz, 2H), 6.91 (d,
J = 8.2, Hz, 1H), 4.64 (s, 1H), 3.93 (s, 3H), 3.90 (s, 3H), 2.64−2.58
(m, 2H), 2.40−2.39 (m, 2H), 1.59 (s, 4H), 1.50 (s, 2H), 1.30 (s, 9H);
13C NMR (50 MHz, CDCl3) δ 151.3, 148.3, 142.5, 136.8, 134.1, 130.5,
129.8, 127.4, 126.7, 125.3, 122.2, 120.5, 113.6, 110.7, 87.6, 86.5, 59.4,
56.1, 50.4, 34.8, 31.3, 26.4, 24.6 ppm; HRMS (ESI) calcd for
C32H38O2N [M + H] 468.2902 found 468.2879.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C NMR spectra for all final compounds and 2D
spectra of 2d. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: bijoy_kundu@yahoo.com,; b_kundu@cdri.res.in.
■
ACKNOWLEDGMENTS
■
M.S. and P.K.A. are thankful to CSIR, New Delhi, India for
fellowships. The authors would like to thank SAIF, CDRI, India
for providing analytical data. CDRI communication No. 8151
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