Lewis acid mediated intramolecular C-C bond formation of alkyne-epoxide leading to six-membered nitrogen and oxygen heterocycles

Article abstract of DOI:10.1021/jo402550e

Intramolecular C-C bond formation of oxygen- and nitrogen-tethered alkynes and epoxide mediated by Lewis acid under ambient conditions is described. A simple procedure for the synthesis of 3,6- and 5,6-dihydropyrans and 3,4-dehydropiperidines from acyclic

Full text of DOI:10.1021/jo402550e

Note
pubs.acs.org/joc
Lewis Acid Mediated Intramolecular C−C Bond Formation of Alkyne-
Epoxide Leading to Six-Membered Nitrogen and Oxygen
Heterocycles
Priya Ghosh, Pipas Saha, Somasekhar Bondalapati, Kiran Indukuri, and Anil K. Saikia*
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, India
S
* Supporting Information
ABSTRACT: Intramolecular C−C bond formation of oxy-
gen- and nitrogen-tethered alkynes and epoxide mediated by
Lewis acid under ambient conditions is described. A simple
procedure for the synthesis of 3,6- and 5,6-dihydropyrans and
3,4-dehydropiperidines from acyclic building blocks in good
yields without using any transition metal is shown.
yclic ethers have undoubtedly attracted the interest of
synthetic chemists due to their occurrence in many
dichloromethane at room temperature, and the reaction
proceeded smoothly to afford 2a in 68% yield, the structure
of which was determined by NMR and X-ray analysis.15
Oxygen-tethered16 and nitrogen-tethered17 alkyne-epoxide
substrates were prepared using previously described methods.
In order to optimize the reaction conditions alkyne-epoxide
1a was subjected to reaction with several Lewis and Bronsted
acids (Table 1). It was observed that apart from BF3·Et2O,
InCl3 and Bi(OTf)3 also resulted in the desired product in good
yields. Zn(OTf)2 and In(OTf)3 gave 28% and 20% yield,
respectively. Brønsted acid CSA gave low yield, but TfOH gave
moderate yield. FeCl3 yielded only 25% of the desired product.
However, reaction using TMSOTf was unsuccessful, and
decomposed product was observed. BF3·Et2O at 0.2 equiv
was found to be the best reagent for the reaction. Survey of the
various solvents revealed that THF and dioxane gave relatively
lower yields, and no progress in the reaction was noticed in
toluene and acetonitrile. Dichloromethane (DCM) proved to
be better than all other solvents. The reaction was also
performed at −20 °C in CH2Cl2 for 10 h but gave only 50%
yield.
Having obtained the optimized conditions, we further
examined the scope of the reaction with variety of substrates
(Table 2). During the course of this study, we noticed that
varying the substitution of methyl and phenyl groups on the
epoxide ring resulted in the products with different
dihydropyrans and 3,4-dehydropiperidines along with some
decomposed products. It was observed from Table 2 that 1,2-
disubstituted (entries 1−3, 6, 7, 10) and terminal epoxides
(entries 4 and 5) gave dihydropyrans in good yields. Substrates
1a, 1b, 1d−g, and 1j (entries 1, 2, 4−7, 10) gave 5,6-
C
natural products exhibiting several important biological
activities.1 Similarly, nitrogen heterocyclic compounds are
important in synthetic chemistry because of their presence in
many biologically active natural products and pharmaceuticals.2
Cyclic ethers are prepared in high yield by either C−C3 or C−
O4 bond formation. Numerous synthetic approaches have been
proposed and used for the preparation of five- and six-
membered oxygen and nitrogen rings, and strategies such as
carbocyclization of enynes promoted by various transition
metal catalysts such as Cu,5 Pd,6 Pt,7 and Au,8 reductive
coupling of alkyne and epoxide using Ni,9 and intramolecular
alkene-epoxide cyclization10 have been well explored. In this
paper intramolecular C−C bond formation of oxygen- and
nitrogen-tethered alkynes and epoxides mediated by Lewis acid
under ambient conditions is described.
In continuation of our interest in oxygen and nitrogen
heterocycles,11 we were in search of methods for synthesizing
multifunctional oxygen and nitrogen heterocyclic frameworks.
Literature reports revealed that cyclization of enyne is one of
the best method for achieving such goals.7b,8 Di- and
tetrahydropyrans can also be synthesized using epoxides and
homoallylic alcohols under Prins cyclization conditions.12
Taking clues from these we envisioned that functionalized
oxygen and nitrogen heterocyclic compounds could be
prepared from O- and N-tethered alkyne-epoxide substrates
mediated by Lewis acid. Although there are reports for the
synthesis of O- and N-heterocyclic compounds from alkyne-
epoxide coupling via intramolecular alkyne−azide cyclo-
additions13 and nickel-catalyzed reductive coupling of alkyne-
epoxide,14 to our knowledge the synthetic potential of the use
of a Lewis acid for the synthesis of such rings using substrates
with an epoxide and an alkyne has not been examined so far.
To start with, alkyne-epoxide 1a was treated with BF3·Et2O in
Received: November 18, 2013
Published: April 10, 2014
© 2014 American Chemical Society
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Note
dihydropyrans, whereas substrate 1c (entry 3) gave 3,6-
dihydropyran 2c. The formation of 2c might be due to higher
stability of the conjugated enone 3,6-dihydropyran compared to
5,6-dihydropyran. Unsubstituted alkyne 1h (entry 8) was found
to be unreactive under the same reaction conditions. Similarly,
terminal methyl-substituted alkyl-epoxide 1i (entry 9) did not
give any product. This is attributed to the lower stability of the
carbocation A (Scheme 1), formed from methyl-substituted
epoxide compared to the aryl-substituted epoxide.12 Alkyl-
substituted alkyne-epoxide 1f and 1g (entries 6 and 7) gave
74% and 76% yields, respectively. Thiophene-substituted
alkyne-epoxide 1j (entry 10) also worked well, giving 60%
yield. Similarly, N-tethered epoxides 1k−q (entries 11−17)
having alkyl and aryl substituents gave 3,4-dehydropiperidines
2k−q in good yields.
The mechanism of the reaction can be explained as follows.
The epoxide 1 in the presence of BF3·Et2O opens up to
generate carbocation A, which after rearrangement gives most
stable oxocarbenium ions B and F via phenyl and hydrogen
migration, respectively.18 The oxocarbenium ions B and F are
then attacked by alkyne group, via a 6-exo-trig cyclization to
give carbocations C and G, respectively. The intermediates C
and G are then trapped by water to give enols D and H, which
Table 1. Optimization of the Reaction
a
entry Lewis/Brønsted acid (equiv) time (h)
solvent
% yield
1
BF3·Et2O (1)
InCl3 (1)
3
3
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
THF
68
65
63
trace
68
68
d
2
3
Bi(OTf)3 (0.5)
TMSOTf (0.5)
BF3·Et2O (0.5)
BF3·Et2O (0.2)
BF3·Et2O (0.2)
BF3·Et2O (0.2)
BF3·Et2O (0.2)
Zn(OTf)2 (1)
CSA (1)
3
4
8
5
3
6
3
7
3
8
3
Toluene
CH3CN
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
d
9
8
d
10
11
12
13
14
10
8
28
32
50
25
20
TfOH (1)
5
FeCl3 (1)
10
8
In(OTf)3 (1)
a
Yields refer to isolated yield. The compounds were characterized by
IR, NMR, and mass spectrometry. d = decomposed product.
Table 2. BF3·Et2O-Mediated Intramolecular C−C Bond Formation of Alkyne and Epoxide
a
1
Yield refers to isolated yield. The compounds are characterized by IR, H, 13C NMR and mass spectrometry. d = Decomposed product.
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Note
Scheme 1. Mechanism of the Reaction
solution of Na2SO3 was added to quench excess mCPBA. Dichloro-
methane was added to the reaction mixture, washed with saturated
sodium bicarbonate and brine solution, and dried over anhydrous
Na2SO4. Evaporation of the solvent gave the crude product, which was
purified by neutral alumina using ethyl acetate and hexane as eluents.
2-Phenyl-3-(((3-(p-tolyl)prop-2-yn-1-yl)oxy)methyl)oxirane (1b).
after rearrangement give ketones E and I. The ketone E after
elimination gives the final compound 2 (Scheme 1). On the
other hand, ketone I initially forms compound J and then
rearranges to give more stable compound 2.
Conclusion. In conclusion, we have developed a mild and
an efficient method for the synthesis of six-membered oxygen
and nitrogen heterocyclic compounds by intramolecular C−C
bond formation of alkyne-epoxide mediated by boron
trifluoride etherate. The method is highly substrate-specific
and works well for alkyl- and aryl-substituted alkyne-epoxide
substrates.
1
Colorless oil; Rf (hexane/EtOAc 9:1) 0.60; yield 242 mg, 87%; H
NMR (400 MHz, CDCl3) δ 7.34−7.26 (m, 7 H), 7.11 (d, J = 8 Hz, 2
H), 4.47 (s, 2 H), 3.97 (dd, J = 11.6 and 3.6 Hz, 1 H), 3.84 (d, J = 1.6
Hz, 1 H), 3.76 (dd, J = 11.6 and 4.8 Hz, 1 H), 3.29−3.26 (m, 1 H),
2.34 (s, 3 H); 13C NMR (75 MHz, CDCl3) δ 138.6, 136.6, 131.6,
128.5, 128.4, 128.2, 125.5, 119.2, 86.8, 83.7, 69.3, 60.9, 59.3, 55.9, 21.4.
IR (KBr, neat) 2922, 2851, 1256, 1098, 1073, 749, 697 cm−1; HRMS
(ESI) m/z calcd for C19H19O2 (M + H)+ 279.1385, found 279.1387.
2-Methyl-3-phenyl-2-(((3-phenylprop-2-yn-1-yl)oxy)methyl)-
oxirane (1c). Colorless oil; Rf (hexane/EtOAc 9:1) 0.50; yield 242 mg,
87%; 1H NMR (600 MHz, CDCl3) δ 7.47- 7.26 (m, 10 H), 4.49 (s, 2
H), 4.23 (s, 1 H), 3.79 (d, J = 10.8 Hz, 1 H), 3.75 (d, J = 10.8 Hz, 1
H), 1.15 (s, 3 H); 13C NMR (150 MHz, CDCl3) δ 135.8, 132.0, 128.6,
128.5, 128.3, 127.9, 126.6, 122.7, 86.9, 85.0, 73.9, 62.1, 61.5, 59.2, 20.3;
IR (KBr, neat) 2926, 2853, 1490, 1255, 1092, 1027, 700 cm−1; HRMS
(ESI) m/z calcd for C19H19O2 (M + H)+ 279.1385, found 279.1386.
2-Methyl-2-(((3-phenylprop-2-yn-1-yl)oxy)methyl)oxirane (1d).
EXPERIMENTAL SECTION
■
1
General Experimental Section. H and 13C NMR spectra were
recorded in CDCl3 on 600, 400, 300 and 150, 100, 75 MHz NMR
spectrometers, respectively, using TMS as internal standard. HRMS
spectra were recorded using a TOF mass spectrometer. Compounds
1a and 1h are known and were prepared according to the literature
procedure.13,15 Their IR, NMR, and HRMS data agreed well with the
reported data. The same procedure was used to prepare compounds
1b−1g, 1i, and 1j.13,15 N-Tethered compounds 1k−1q were prepared
as per the literature procedures.13,15,16
1
General Procedure for Preparation of O-Tethered Com-
pounds. In an oven-dried round-bottom flask was taken NaH (1.5
equiv), and dry THF (20 mL) was added to it. To this a solution of
propargyl alcohol (1 equiv) or its derivatives was added slowly. The
reaction mixture was stirred for 0.5 h at 0 °C. Allyl bromide (1 equiv)
was added to the reaction mixture dropwise. The reaction was
monitored by thin layer chromatography, and after completion of the
reaction THF was removed by evaporation. The residue was extracted
with ethyl acetate (30 mL) and washed with water and brine solution
(20 mL × 2). The organic layer was dried over anhydrous Na2SO4,
and solvent was evaporated using a rotary evaporator to give crude
product. The crude product was purified on silica gel column
chromatography using ethyl acetate and hexane as eluents. The ether
(1.0 equiv) thus obtained was treated with metachloroperbenzoic acid
(1.5 equiv) in dichloromethane (15 mL) at 0 °C. The reaction mixture
was brought to room temperature and stirred for a specific time. After
completion of the reaction as determined by TLC, a saturated aqueous
Colorless oil; Rf (hexane/EtOAc 9:1) 0.60; Yield 186 mg, 92%; H
NMR (600 MHz, CDCl3) δ 7.45- 7.31 (m, 5 H), 4.43 (d, J = 2.4 Hz, 2
H), 3.69 (d, J = 11.2 Hz, 1 H), 3.58 (d, J = 11.2 Hz, 1 H), 2.81 (d, J =
4.8 Hz, 1 H), 2.64 (d, J = 4.8 Hz, 1 H), 1.42 (s, 3 H); 13C NMR (150
MHz, CDCl3) δ 131.9, 128.7, 128.5, 122.7, 86.7, 84.9, 73.2, 59.4, 56.0,
51.8, 18.7; IR (KBr, neat) 2916, 2848, 1255, 1095, 757 cm−1; HRMS
(ESI) m/z calcd for C13H15O2 (M + H)+ 203.1072, found 203.1069.
2-Phenyl-2-(((3-phenylprop-2-yn-1-yl)oxy)methyl)oxirane (1e).
1
Colorless oil; Rf (hexane/EtOAc 9:1): 0.50; Yield 248 mg, 94%; H
NMR (300 MHz, CDCl3) δ 7.58−7.15 (m, 10 H), 4.47 (s, 2 H), 4.20
(d, J = 11.4 Hz, 1 H), 3.95 (d, J = 11.4 Hz, 1 H), 3.20 (d, J = 5.4 Hz, 1
H), 2.83 (d, J = 5.4 Hz, 1 H); 13C NMR (75 MHz, CDCl3) δ 137.6,
131.7, 128.5, 128.4, 128.3, 127.4, 126.2, 122.4, 86.6, 84.6, 71.4, 59.3,
58.8, 53.3; IR (KBr, neat) 2925, 2854, 1490, 1256, 1098, 1027, 698
cm−1; HRMS (ESI) m/z calcd for C18H17O2 (M + H)+ 265.1229,
found 265.1228.
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Note
2-((But-2-yn-1-yloxy)methyl)-3-phenyloxirane (1f). Colorless oil;
Rf (hexane/EtOAc 9:1): 0.50; Yield 213 mg, 95%; H NMR (400
crude product, which was purified by neutral alumina using ethyl
acetate and hexane as eluents.
1
MHz, CDCl3) δ 7.36−7.26 (m, 5 H), 4.21 (s, 2 H), 3.87 (dd, J = 11.6
and 3.2 Hz, 1 H), 3.82 (brs, 1 H), 3.67 (dd, J = 11.6 and 4.8 Hz, 1 H),
3.24 (t, J = 2.4 Hz, 1 H), 1.85 (s, 3 H). 13C NMR (100 MHz, CDCl3)
δ 136.8, 128.5, 128.3, 125.7, 83.0, 74.8, 69.2, 60.8, 59.1, 55.9, 3.6; IR
(KBr, neat) 2920, 1497, 1461, 1357, 1139, 1095, 1023, 698 cm−1;
HRMS (ESI+) calcd for C13H14O2 (M + Na)+ 225.0886, found
225.0885.
4-Methyl-N-((2-methyloxiran-2-yl)methyl)-N-(undec-2-yn-1-yl)-
benzenesulfonamide (1k). Colorless oil; Rf (hexane/EtOAc 9:1) 0.45;
yield 352 mg, 90%; 1H NMR (400 MHz, CDCl3) δ 7.71 (d, J = 7.2 Hz,
2 H), 7.26 (d, J = 7.2 Hz, 2 H), 4.23 (d, J = 18.4 Hz, 1 H), 4.12 (d, J =
18.4 Hz, 1 H), 3.28 (s, 2 H), 2.75 (d, J = 4.4 Hz, 1 H), 2.62 (d, J = 3.6
Hz, 1 H), 2.39 (s, 3 H), 1.82 (t, J = 6.0 Hz, 2 H), 1.39 (s, 3 H), 1.28−
1.14 (m, 12 H), 0.87 (t, J = 6.8 Hz, 3 H); 13C NMR (100 MHz,
CDCl3) δ 143.5, 136.2, 129.5, 128.0, 86.7, 72.3, 55.7, 51.9, 50.9, 38.4,
32.0, 29.3, 29.2, 28.9, 28.4, 22.8, 21.6, 19.0, 18.6, 14.3; IR (KBr, neat)
2927, 2856, 1442, 1351, 1164, 1090, 1047, 658 cm−1; HRMS (ESI) m/
z calcd for C22H34NO3S (M + H)+ 392.2254, found 392.2261.
4-Methyl-N-((3-phenyloxiran-2-yl)methyl-N-(3-phenylprop-2-yn-
1-yl)benzenesulfonamide (1l). Colorless oil; Rf (hexane/EtOAc 4:1)
2-Phenyl-3-((undec-2-yn-1-yloxy)methyl)oxirane (1g). Colorless
1
oil; Rf (hexane/EtOAc 9:1): 0.60; Yield 276 mg, 92%; H NMR (400
MHz, CDCl3) δ 7.34−7.25 (m, 5 H), 4.23 (s, 2 H), 3.87 (d, J = 11.2
Hz, 1 H), 3.81 (s, 1 H), 3.68 (dd, J = 11.2 and 5.2 Hz, 1 H), 3.23 (d, J
= 1.6 Hz, 1 H), 2.21 (t, J = 5.6 Hz, 2 H), 1.54−1.47 (m, 2 H), 1.41−
1.20 (m, 10 H), 0.87 (t, J = 6.4 Hz, 3 H); 13C NMR (100 MHz,
CDCl3) δ 136.9, 128.6, 128.3, 125.8, 87.8, 75.5, 69.2, 60.9, 59.2, 56.1,
31.9, 29.5, 29.2, 29.0, 28.7, 22.8, 18.9, 14. 2; IR (KBr, neat) 2927,
2855, 1461, 1357,1137, 1095, 750, 698 cm−1; HRMS (ESI) m/z calcd
for C20H29O2 (M + H)+ 301.2162, found 301.2158.
1
0.40; yield 342 mg, 82%; H NMR (600 MHz, CDCl3) δ 7.78 (d, J =
8.4 Hz, 2 H), 7.35−7.21 (m, 10 H), 7.06 (d, J = 7.2 Hz, 2 H), 4.52 (d,
J = 18.6 Hz, 1 H), 4.44 (d, J = 18.6 Hz, 1 H), 3.74 (d, J = 2.4 Hz, 1 H),
3.58 (d, J = 3.6 Hz, 2 H), 3.26 (dt, J = 4.8 and 4.2 Hz, 1 H), 2.34 (s, 3
H); 13C NMR (150 MHz, CDCl3) δ 143.8, 136.3, 135.8, 131.5, 129.6,
128.6, 128.5, 128.4, 128.2, 127.8, 125.7, 122.0, 86.0, 81.7, 60.5, 57.0,
48.0, 39.0, 21.4; IR (KBr, neat) 2922, 2851, 1643, 1447, 1383, 1265
cm−1; HRMS (ESI) m/z calcd for C25H24NO3S (M + H)+ 418.1477,
found 418.1474.
4-Methyl-N-((3-phenyloxiran-2-yl)methyl)-N-(3-(p-tolyl)prop-2-
yn-1-yl)benzenesulfonamide (1m). Colorless oil; Rf (hexane/EtOAc
4:1) 0.45; yield 357 mg, 83%; 1H NMR (600 MHz, CDCl3) δ 7.70 (d,
J = 8.4 Hz, 2 H), 7.27−7.11 (m, 7 H), 6.96 (d, J = 8.4 Hz, 2 H), 6.88
(d, J = 8.4 Hz, 2 H), 4.44 (d, J = 18.0 Hz, 1 H), 4.34 (d, J = 18.0 Hz, 1
H), 3.74 (d, J = 1.2 Hz, 1 H), 3.50 (dd, J = 12.0 and 4.8 Hz, 2 H), 3.17
(dt, J = 5.4 and 4.2 Hz, 1 H), 2.27 (s, 3 H), 2.26 (s, 3 H); 13C NMR
(150 MHz, CDCl3) δ 143.9, 138.9, 136.5, 131.6, 129.8, 129.1, 128.7,
128.6, 127.6, 127.5, 125.8, 119.2, 86.3, 81.2, 60.6, 57.3, 48.2, 39.2, 21.7
(2C); IR (KBr, neat) 2922, 2851, 1462, 1349, 1163, 1090, 843, 744
cm−1; HRMS (ESI) m/z calcd for C26H26NO3S (M + H)+ 432.1633,
found 432.1639.
2-Methyl-3-(((3-(p-tolyl)prop-2-yn-1-yl)oxy)methyl)oxirane (1i).
1
Colorless oil; Rf (hexane/EtOAc 9:1) 0.50; yield 194 mg, 90%; H
NMR (600 MHz, CDCl3) δ 7.30 (d, J = 8.0 Hz, 2 H), 7.11 (d, J = 8.0
Hz, 2 H), 4.41 (d, J = 9.6 Hz, 2 H), 3.80 (dd, J = 10.8 and 3.0 Hz, 1
H), 3.60 (dd, J = 11.4 and 5.4 Hz, 1 H), 2.93−2.97 (m, 2 H), 2.34 (s, 3
H), 1.33 (d, J = 7.0 Hz, 3 H); 13C NMR (150 MHz, CDCl3) δ 138.7,
131.7, 129.1, 119.4, 86.8, 83.9, 69.9, 59.3, 57.6, 52.3, 21.5, 17.3; IR
(KBr, neat) 2924, 2855, 1510, 1356, 1258, 1120, 1091, 817, 753 cm−1;
HRMS (ESI) m/z calcd for C14H17O2 (M + H)+ 217.1229, found
217.1227.
2-Phenyl-3-(((3-(thiophen-2-yl)prop-2-yn-1-yl)oxy)methyl)-
oxirane (1j). Colorless oil; Rf (hexane/EtOAc 9:1) 0.50; yield 238 mg,
88%; 1H NMR (400 MHz, CDCl3) δ 7.37−7.22 (m, 7 H), 6.99−6.96
(dd, J = 4.8 and 3.6 Hz, 1 H), 4.50 (s, 2 H), 3.97 (dd, J = 11.2 and 3.2
Hz, 1 H), 3.85 (d, J = 1.6 Hz, 1 H), 3.75 (dd, J = 11.2 and 4.8 Hz, 1
H), 3.29−3.26 (m, 1 H); 13C NMR (100 MHz, CDCl3) δ 136.8,
132.7, 128.6, 128.4, 127.6, 127.1, 125.8, 122.4, 88.8, 80.1, 69.5, 60.9,
59.5, 56.0; IR (KBr, neat) 2923, 2854, 1674, 1463, 1359, 1190, 1098,
848, 697 cm−1; HRMS (ESI) m/z calcd for C16H15O2S (M + H)+
271.0787, found 271.0789.
General Procedure for the Synthesis of N-Tethered
Compounds. To an oven-dried round-bottom flask with magnetic
stir bar were added allyl bromide (1.1 equiv), 4-methylbenzenesulfo-
namide (1 equiv), K2CO3 (2 equiv), and acetone (20 mL). The round-
bottom flask was heated at 60 °C. Upon completion of the reaction
(16 h), the solution was cooled to room temperature, filtered through
a short plug of Celite, and washed with EtOAc, and solvent was
removed in vacuo to afford a crude product. Purification of the
resulting crude residue via silica gel flash column chromatography
afforded the desired N-toysl allylic amine. In an oven-dried round-
bottom flask was taken NaH (1.5 equiv), and dry THF (20 mL) was
added to it. To this a solution of N-tosyl allylic amine (1 equiv) or its
derivatives was added slowly. The reaction mixture was stirred for 0.5
h at 0 °C. Propargyl bromide (1 equiv) was added to the reaction
mixture dropwise. The reaction was monitored by thin layer
chromatography, and after completion of the reaction THF was
removed by evaporation. The residue was extracted with ethyl acetate
(30 mL) and washed with water and brine solution (20 mL × 2). The
organic layer was dried over anhydrous Na2SO4, and solvent was
evaporated using a rotary evaporator to obtain crude product. The
crude product was purified by silica gel column chromatography using
ethyl acetate and hexane as eluents to give the N-tethered product.
The product (1.0 equiv) thus obtained was treated with m-
chloroperbenzoic acid (1.5 equiv) in dichloromethane at 0 °C. The
reaction mixture was brought to room temperature and stirred for a
specific time. After completion of the reaction as determined by TLC,
a saturated aqueous solution of Na2SO3 was added to quench excess
mCPBA. Dichloromethane (30 mL) was added to the reaction
mixture, washed with saturated sodium bicarbonate and brine solution,
and dried over anhydrous Na2SO4. Evaporation of the solvent gave the
4-Methyl-N-((2-phenyloxiran-2-yl)methyl)-N-(3-(p-tolyl)prop-2-
yn-1-yl)benzenesulfonamide (1n). Colorless oil; Rf (hexane/EtOAc
4:1) 0.50; yield 371 mg, 89%; 1H NMR (600 MHz, CDCl3) δ 7.75 (d,
J = 8.4 Hz, 2 H), 7.48 (d, J = 8.4 Hz, 2 H), 7.38 (t, J = 8.4 Hz, 3 H),
7.25- 7.19 (m, 5 H), 7.00 (d, J = 8.4 Hz, 2 H), 4.38 (brs, 2 H), 3.97 (d,
J = 15 Hz, 1 H), 3.74 (d, J = 15.0 Hz, 1 H), 3.27 (d, J = 5.4 Hz, 1 H),
2.83 (d, J = 5.4 Hz, 1 H), 2.32 (s, 3 H); 13C NMR (150 MHz, CDCl3)
δ 143.9, 137.6, 136.2, 131.7, 129.8, 128.7, 128.6, 128.4, 128.3, 128.1,
126.5, 122.4, 86.0, 82.0, 59.4, 53.3, 49.5, 39.2, 21.6; IR (KBr, neat)
2923, 2853, 1447, 1350, 1161, 1027, 757, 696 cm−1; HRMS (ESI) m/z
calcd for C25H24NO3S (M + H)+ 418.1477, found 418.1476.
4-Methyl-N-((2-methyloxiran-2-yl)methyl-N-(3-phenylprop-2-yn-
1-yl)benzenesulfonamide (1o). Colorless oil; Rf (hexane/EtOAc 4:1)
1
0.50; yield 298 mg, 84%; H NMR (600 MHz, CDCl3) δ 7.76 (d, J =
8.1 Hz, 2 H), 7.34- 7.20 (m, 5 H), 7.00 (d, J = 8.1 Hz, 2 H), 4.48 (d, J
= 18.6 Hz, 2 H), 4.40 (d, J = 18.6 Hz, 1 H), 3.39 (d,, J = 13.2 Hz, 2 H),
2.82 (d, J = 4.8 Hz, 1 H), 2.67 (d, J = 4.8 Hz, 1 H), 2.33 (s, 3 H), 1.45
(s, 3 H); 13C NMR (75 MHz, CDCl3) δ 143.6, 135.8, 131.4, 129.5,
128.4, 128.0, 127.7, 122.0, 85.8, 81.5, 55.7, 51.6, 50.9, 38.6, 21.4, 18.9.
IR (KBr, neat) 2923, 2853, 1491, 1349, 1162, 1090, 1027, 757 cm−1;
HRMS (ESI) m/z calcd for C20H22NO3S (M + H)+ 356.1320, found
356.1315.
4-Methyl-N-((2-methyloxiran-2-yl)methyl-N-(3-(p-tolyl)prop-2-
yn-1-yl)benzenesulfonamide (1p). Colorless oil; Rf (hexane/EtOAc
4:1) 0.50; yield 306 mg, 83%; 1H NMR (600 MHz, CDCl3) δ 7.75 (d,
J = 8.4 Hz, 2 H), 7.25 (d, J = 8.4 Hz, 2 H), 7.02 (d, J = 8.0 Hz, 2 H),
6.91 (d, J = 8.0 Hz, 2 H), 4.47 (d, J = 18.6 Hz, 1 H), 4.39 (d, J = 18.6
Hz, 1 H), 3.39 (s, 2 H), 2.81 (d, J = 4.2 Hz, 1 H), 2.66 (d, J = 4.8 Hz, 1
H), 2.33 (s, 3 H), 2.32 (s, 3 H), 1.43 (s, 3 H); 13C NMR (150 MHz,
CDCl3) δ 143.6, 138.6, 136.0, 131.4, 129.6, 128.8, 127.8, 119.0, 86.0,
80.9, 55.7, 51.7, 51.0, 38.7, 21.4 (2C), 19.0; IR (KBr, neat) 2921, 2851,
1348, 1162, 1090, 1039, 844, 743 cm−1; HRMS (ESI) m/z calcd for
C21H24NO3S (M + H)+ 370.1477, found 370.1476.
4122
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The Journal of Organic Chemistry
Note
N-(3-(4-methoxyphenyl)prop-2-yn-1-yl)-4-methyl-N-((2-methyl-
H), 6.98 (brs, 1 H), 4.48 (d, J = 16.8 Hz, 1 H), 4.42 (d, J = 16.8 Hz, 1
H), 4.06 (dd, J = 11.6 and 5.2 Hz, 1 H), 3.74−3.69 (m, 1 H), 3.56 (dd,
J = 10.8 and 7.6 Hz, 1 H), 2.33 (s, 3 H); 13C NMR (100 MHz,
CDCl3) δ 197.8, 140.5, 140.1, 138.6, 129.0, 128.3, 127.5, 70.2, 64.6,
41.9, 25.2; IR (KBr, neat) 2922, 2850, 1667, 1389, 1239, 1107, 701
cm−1; HRMS (ESI) m/z calcd for C13H14O2 (M + Na)+ 225.0886,
found 225.0871.
oxiran-2-yl)methyl)benzenesulfonamide (1q). Colorless oil; Rf
1
(hexane/EtOAc 4:1) 0.50; yield 315 mg, 82%; H NMR (600 MHz,
CDCl3) δ 7.75 (d, J = 7.8 Hz, 2 H), 7.25 (d, J = 8.4 Hz, 2 H), 6.96 (d,
J = 8.4 Hz, 2 H), 6.75 (d, J = 8.4 Hz, 2 H), 4.46 (d, J = 18.6 Hz, 1 H),
4.37 (d, J = 18.6 Hz, 1 H), 3.78 (s, 3 H), 3.38 (s, 2 H), 2.82 (d, J = 4.8
Hz, 1 H), 2.66 (d, J = 4.8 Hz, 1 H), 2.34 (s, 3 H), 1.44 (s, 3 H); 13C
NMR (150 MHz, CDCl3) δ 159.8, 143.8, 136.2, 133.1, 130.1, 129.7,
114.4, 113.9, 85.9, 80.4, 55.9, 55.5, 51.9, 51.2, 38.9, 21.6, 19.1; IR (KBr,
neat) 2923, 2850, 1606, 1509, 1348, 1248, 1162, 1031, 750 cm−1;
HRMS (ESI) m/z calcd for C21H24NO4S (M + H)+ 386.1426, found
386.1422.
General Procedure for Lewis Acid Catalyzed Intramolecular
C−C Bond Formation of Alkyne-Epoxide. To a corresponding
alkyne-epoxide substrates (1.0 equiv) in CH2Cl2 (5 mL) at 0 °C was
added BF3·Et2O (0.2 equiv) dropwise, and the reaction mixture was
brought to room temperature. The reaction was continued for a
specified time and monitored by TLC. After completion of the
reaction, the reaction mixture was treated with saturated sodium
bicarbonate solution (5 mL). The product was extracted with CH2Cl2
(2 × 10 mL) and washed with brine. Organic layer was separated and
dried over anhydrous Na2SO4 and evaporated using rotary evaporator
to obtain the crude product. The crude product was purified by silica
gel column chromatography using ethyl acetate and hexane as eluents
to afford the cyclic compounds 2.
1-(5-Phenyl-5,6-dihydro-2H-pyran-3-yl)nonan-1-one (2g). Yellow
1
oil; Rf (hexane/EtOAc 9:1) 0.50; yield 228 mg, 76%; H NMR (400
MHz, CDCl3) δ 7.37−7.33 (m, 2 H), 7.30−7.27 (m, 1 H), 7.23−7.20
(m, 2 H), 6.97 (brs, 1 H), 4.47 (d, J = 16.4 Hz, 1 H), 4.39 (d, J = 16.4
Hz, 1 H), 4.04 (dd, J = 13.6 and 5.6 Hz, 1 H), 3.74−3.66 (m, 1 H),
3.53 (dd, J = 10.8 and 7.2 Hz, 1 H), 2.65 (t, J = 16.4 Hz, 2 H), 1.65−
1.58 (m, 2 H), 1.32−1.20 (m, 10 H), 0.87 (t, J = 7.2 Hz, 3 H); 13C
NMR (100 MHz, CDCl3) δ 200.3, 140.2, 139.2, 138.2, 129.0, 128.3,
127.5, 70.4, 64.8, 41.9, 37.2, 32.0, 29.5, 29.4, 29.3, 24.7, 22.8, 14.3; IR
(KBr, neat) 2925, 2854, 1667, 1454, 1108, 1024, 700 cm−1; HRMS
(ESI) m/z calcd for C20H29O2 (M + H)+ 301.2162, found 301.2168.
(5-Phenyl-5,6-dihydro-2H-pyran-3-yl)(thiophen-2-yl)methanone
(2j). Pale yellow oil; Rf (hexane/EtOAc 9:1) 0.40; yield 163 mg, 60%;
1H NMR (400 MHz, CDCl3) δ 7.66−7.64 (m, 2 H), 7.41−7.34 (m, 2
H), 7.31−7.27 (m, 3 H), 7.11 (t, J = 3.6 Hz, 1 H), 6.95 (brs, 1 H),
4.60 (brs, 2 H), 4.13 (dd, J = 11.2 Hz, 1 H), 3.82−3.75 (m, 1 H), 3.64
(dd, J = 11.2 and 7.2 Hz, 1 H); 13C NMR (100 MHz, CDCl3) δ 186.9,
142.7, 140.3, 139.8, 138.2, 133.9, 133.6, 129.1, 128.4, 128.1, 127.6,
70.7, 65.4, 42.0; IR (KBr, neat) 2957, 2824, 1621, 1414, 1121, 1052,
700 cm−1; HRMS (ESI) m/z calcd for C16H15O2S (M + H)+ 271.0787,
found 271.0790.
Phenyl(4-phenyl-3,6-dihydro-2H-pyran-3-yl)methanone (2a).
Colorless solid; mp 111−112 °C; Rf (hexane/EtOAc 9:1) 0.50;
1
Yield 179 mg, 68%; H NMR (600 MHz, CDCl3) δ 7.70 (d, J = 7.6
Hz, 1 H), 7.51 (t, J = 7.8 Hz, 1 H), 7.43−7.40 (m, 3 H), 7.34−7.31
(m, 3 H), 7.27 (t, J = 7.8 Hz, 1 H), 7.22 (d, J = 7.8 Hz, 1 H), 6.73 (dd,
J = 1.8 and 1.2 Hz, 1 H), 4.63 (dd, J = 2.4 and 1.8 Hz, 2 H), 4.12 (dd, J
= 11.4 and 5.4 Hz, 1 H), 3.78−3.74 (m, 1 H), 3.63 (dd, J = 11.4 and
7.2 Hz, 1 H); 13C NMR (100 MHz, CDCl3) δ 196.0, 143.0, 140.1,
137.7, 137.5, 132.2, 129.3, 129.0, 128.5, 128.3, 127.5, 70.6, 65.4, 42.1;
IR (KBr, neat) 2923, 2852, 1640, 1447, 1265, 1105, 1047, 742, 700
cm−1; HRMS (ESI) m/z calcd for C18H17O2 (M + H)+ 265.1229
found 265.1229.
(4-Phenyl-3,6-dihydro-2H-pyran-3-yl)(p-tolyl)methanone (2b).
Yellow oil; Rf (hexane/EtOAc 9:1) 0.50; yield 197 mg, 71%; 1H
NMR (600 MHz, CDCl3) δ 7.62 (d, J = 8.0 Hz, 1 H), 7.35- 7.21 (m, 8
H), 6.71 (dd, J = 2.8 and 1.6 Hz,1 H), 4.62 (dd, J = 2.8 and 2.0 Hz, 2
H), 4.12 (dd, J = 11.2 and 5.6 Hz, 1 H), 3.78−3.74 (m, 1 H), 3.63 (dd,
J = 11.2 and 7.2 Hz, 1 H), 2.38 (s, 3 H); 13C NMR (150 MHz,
CDCl3) δ 195.8, 142.1, 140.3, 137.9, 134.8, 130.6, 129.6, 129.4, 129.2,
128.4, 127.5, 70.7, 65.5, 42.1, 21.7; IR (KBr, neat) 2924, 2852, 1641,
1454, 1264, 1106, 759, 7001 cm−1; HRMS (ESI) m/z calcd for
C19H19O2 (M + H)+ 279.1385, found 279.1384.
1-(5-Methyl-1-tosyl-3,4-dehydropiperidin-3-yl)nonan-1-one (2k).
Yellow oil; Rf (hexane/EtOAc 9:1) 0.40; yield 301 mg, 77%; 1H NMR
(400 MHz, CDCl3) δ 7.68 (d, J = 7.6 Hz, 2 H), 7.31 (d, J = 7.6 Hz, 2
H), 6.70 (brs, 1 H), 3.90 (d, J = 16.8 Hz, 1 H), 3.48 (d, J = 18.0 Hz, 1
H), 3.43 (dd, J = 11.6 and 4.4 Hz, 1 H), 2.72−2.64 (m, 1 H), 2.58 (t, J
= 6.8 Hz, 2 H), 2.49 (dd, J = 11.2 and 7.6 Hz, 1 H), 2.41 (s, 3 H),
1.58−1.50 (m, 2 H), 1.30−1.18 (m, 10 H), 1.11 (d, J = 7.2 Hz, 3 H),
0.86 (t, J = 6.8 Hz, 3 H); 13C NMR (100 MHz, CDCl3) δ 199.6, 143.8,
142.3, 134.8, 133.1, 129.9, 127.8, 48.7, 43.8, 36.9, 31.8, 31.2, 29.4, 29.3,
29.2, 24.5, 22.7, 21.6, 17.7, 14.1; IR (KBr, neat) 2925, 2854, 1667,
1459, 1348, 1166, 1025, 657 cm−1; HRMS (ESI) m/z calcd for
C22H34NO3S (M + H)+ 392.2254, found 392.2258.
Phenyl(4-phenyl-1-tosyl-3,4- dehydropiperidin-3-yl)methanone
1
(2l). Yellow oil; (hexane/EtOAc 4:1) 0.30; yield 250 mg, 60%; H
NMR (600 MHz, CDCl3) δ 7.71 (d, J = 8.4 Hz, 2 H), 7.62 (d, J = 7.8
Hz, 2 H), 7.42−7.27 (m, 8 H), 7.15 (d, J = 7.8 Hz, 2 H), 6.63 (s, 1 H),
4.35 (dd, J = 18.0 and 1.8 Hz, 1 H), 3.95−3.89 (m, 2 H), 3.75 (d, J =
16.8 Hz, 1 H), 2.67 (dd, J = 10.8 and 7.2 Hz, 1 H), 2.43 (s, 3 H); 13C
NMR (150 MHz, CDCl3) δ 195.4, 143.9, 139.3, 137.1, 135.3, 132.2,
130.9, 129.9, 129.4, 128.5, 127.9, 127.7, 127.3, 124.4, 114.1, 49.6, 44.5,
42.8, 21.5; IR (KBr, neat) 2922, 2852, 1643, 1163, 1090, 1039, 1026,
761, 670 cm−1; HRMS (ESI) m/z calcd for C25H24NO3S (M + H)+
418.1477, found 418.1477.
(4-Phenyl-1-tosyl-3,4-dehydropiperidin-3-yl)(p-tolyl)methanone
(2m). Yellow oil; Rf (hexane/EtOAc 4:1) 0.35; yield 263 mg, 61%; 1H
NMR (600 MHz, CDCl3) δ 7.69 (d, J = 8.4 Hz, 2 H), 7.55 (d, J = 8.4
Hz, 2 H), 7.36−7.27 (m, 5 H), 7.20 (d, J = 8.4 Hz, 2 H), 7.15 (d, J =
8.4 Hz, 2 H), 6.60 (brs, 1 H), 4.34 (dd, J = 16.8 and 1.8 Hz, 1 H),
3.95−3.88 (m, 2 H), 3.74(d, J = 16.8 Hz, 1 H), 2.64 (dd, J = 12.0 and
7.2 Hz, 1 H), 2.43 (s, 3 H), 2.37 (s, 3 H); 13C NMR (150 MHz,
CDCl3) δ 195.3, 144.1, 143.3, 142.7, 139.5, 135.6, 134.6, 130.1, 129.6,
129.5, 129.3, 129.2, 128.2, 128.0, 114.3, 49.9, 44.8, 42.9, 22.8 (2C); IR
(KBr, neat) 2923, 2853, 1642, 1454, 1348, 1166, 1091, 701 cm−1;
HRMS (ESI) m/z calcd for C26H26NO3S (M + H)+ 432.1633, found
432.1632.
(5-Methyl-4-phenyl-3,6-dihydro-2H-pyran-3-yl)(phenyl)-
methanone (2c). Yellow oil; Rf (hexane/EtOAc 9:1) 0.50; yield 172
1
mg, 62%; H NMR (600 MHz, CDCl3) δ 7.94 (d, J = 7.4 Hz, 1 H),
7.59−7.26 (m, 9 H), 4.48−4.38 (m, 2 H), 4.07 (dd, J = 11.2 and 4.4
Hz, 1 H), 3.87 (dd, J = 11.2 and 4.0 Hz, 1 H), 3.33 (brs, 1 H), 1.45 (s,
3 H); 13C NMR (150 MHz, CDCl3) δ 198.4, 141.4, 137.3, 135.5,
133.8, 133.7, 129.4, 129.1, 128.9, 128.8, 127.3, 71.4, 66.9, 46.5, 19.7; IR
(KBr, neat) 2923, 2852, 1641, 1447, 1265, 1105, 1047, 742, 701 cm−1;
HRMS (ESI) m/z calcd for C19H19O2 (M + H)+ 279.1385, found
279.1383.
(5-Methyl-5,6-dihydro-2H-pyran-3-yl)(phenyl)methanone (2d).
Yellow oil; Rf (hexane/EtOAc 9:1) 0.50; yield 131 mg, 65%; 1H
NMR (400 MHz, CDCl3) δ 7.67−7.65 (m, 2 H), 7.56−7.52 (m, 1 H),
7.47−7.43 (m, 2 H), 6.54 (brs, 1 H), 4.49 (dd, J = 12.0 and 2.0 Hz, 2
H), 3.95 (dd, J = 10.8 and 5.6 Hz, 1 H), 3.34 (dd, J = 10.8 and 7.2 Hz,
1 H), 2.63−2.58 (m, 1 H), 1.06 (d, J = 7.2 Hz, 3 H); 13C NMR (100
MHz, CDCl3) δ 196.0, 146.0, 137.8, 136.9, 132.0, 129.3, 128.4, 70.1,
65.3, 30.3, 16.7; IR (KBr, neat) 2924, 2852, 1641, 1447, 1264, 1111,
1024, 820, 711 cm−1; HRMS (ESI) m/z calcd for C13H15O2 (M + H)+
203.1072, found 203.1074.
(5-Methyl-1-tosyl-3,4-dehydropiperidin-3-yl)(phenyl)methanone
1
(2o). Yellow oil; Rf (hexane/EtOAc 4:1) 0.50; yield 277 mg, 78%; H
NMR (600 MHz, CDCl3) δ 7.73 (d, J = 8.4 Hz, 2 H), 7.58 (d, J = 7.8
Hz, 2 H), 7.53 (t, J = 7.2 Hz, 1 H), 7.43 (t, J = 7.8 Hz, 2 H), 7.35 (d, J
= 7.8 Hz, 2 H), 6.45 (d, J = 4.2 Hz, 1 H), 4.09 (d, J = 16.2 Hz, 1 H),
3.74 (dt, J = 16.8 and 2.4 Hz, 1 H), 3.53 (dd, J = 11.4 and 5.4 Hz, 1
H), 2.71−2.76 (m,1 H), 2.58 (dd, J = 11.4 and 7.8 Hz, 1 H), 2.44 (s, 3
1-(5-Phenyl-5,6-dihydro-2H-pyran-3-yl)ethanone (2f). Yellow oil;
Rf (hexane/EtOAc 9:1) 0.40; yield 166 mg, 74%; 1H NMR (400 MHz,
CDCl3) δ 7.387.34 (m, 2 H), 7.32−7.29 (m, 1 H), 7.26−7.22 (m, 2
4123
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Note
H), 1.10 (d, J = 7.2 Hz, 3 H); 13C NMR (75 MHz, CDCl3) δ 195.4,
146.3, 143.7, 137.2, 132.8, 131.4, 129.9, 129.6, 128.7, 128.0, 127.5,
48.7, 44.3, 31.1, 21.5, 17.5; IR (KBr, neat) 2964, 2926, 1644, 1346,
1167, 1091, 713 cm−1; HRMS (ESI) m/z calcd for C20H22NO3S (M +
H)+ 356.1320, found 356.1314.
(4) (a) Nicolaou, K. C.; Hwang, C. K.; Nugiel, D. A. J. Am. Chem.
Soc. 1989, 111, 4136−4137. (b) Nicolaou, K. C.; Hwang, C. K.;
Duggan, M. E.; Nugiel, D. A.; Abe, Y.; Bal Reddy, K.; DeFrees, S. A.;
Reddy, D. R.; Awartani, R. A. J. Am. Chem. Soc. 1995, 117, 10227−
10238.
(5-Methyl-1-tosyl-3,4-dehydropiperidin-3-yl)(p-tolyl)methanone
(5) Gao, P.; Yan, X.-B.; Tao, T.; Yang, F.; He, T.; Song, X.-R.; Liu,
X.-Y.; Liang, Y.-M. Chem.Eur. J. 2013, 19, 14420−14424.
(6) (a) Trost, B. M.; Tanoury, G. J. J. Am. Chem. Soc. 1988, 110,
1636−1638. (b) Mikami, K.; Hatano, M. Proc. Natl. Acad. Sci. U.S.A.
1
(2p). Yellow oil; Rf (hexane/EtOAc 4:1) 0.4; yield 278 mg, 75%; H
NMR (600 MHz, CDCl3) δ 7.73 (d, J = 8.4 Hz, 2 H), 7.51 (d, J = 8.4
Hz, 2 H), 7.34 (d, J = 8.4 Hz, 2 H), 7.23 (d, J = 8.4 Hz, 2 H), 6.42 (d, J
= 3.0 Hz, 1 H), 4.08 (d, J = 16.8 Hz, 1 H), 3.74 (dt, J = 16.8 and 2.4
Hz, 1 H), 3.53 (dd, J = 11.4 and 5.4 Hz, 1 H), 2.70−2.78 (m, 1 H),
2.57 (dd, J = 11.4 and 7.2 Hz, 1 H), 2.43 (s, 3 H), 2.41 (s, 3 H), 1.09
(d, J = 7.2 Hz, 3 H); 13C NMR (150 MHz, CDCl3) δ 195.4, 145.6,
144.0, 143.1, 134.8, 134.2, 133.4, 130.0, 129.6, 129.2, 128.0, 49.0, 44.7,
31.4, 21.8, 21.7, 17.9; IR (KBr, neat) 2925, 2854, 1727, 1643, 1605,
1347, 1167, 1091, 745 cm−1; HRMS (ESI) m/z calcd for C21H24NO3S
(M + H)+ 370.1477, found 370.1477.
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Lett. 2012, 14, 3538−3541.
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ez-Nunez, E.; Echavarren, A. M. Chem. Rev. 2008, 108,
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(4-Methoxyphenyl)(5-methyl-1-tosyl-3,4-dehydropiperidin-3-yl)-
methanone (2q). Yellow oil; Rf (hexane/EtOAc 4:1) 0.35; yield 281
1
mg, 73%; H NMR (600 MHz, CDCl3) δ 7.73 (d, J = 8.1 Hz, 2 H),
7.64 (d, J = 8.1 Hz, 2 H), 7.34 (d, J = 7.8 Hz, 2 H), 6.91 (d, J = 8.1 Hz,
2 H), 6.38 (d, J = 3.6 Hz, 1 H), 4.07 (d, J = 16.2 Hz, 1 H), 3.87 (s, 3
H), 3.67 (dt, J = 16.8 and 2.4 Hz, 1 H), 3.54 (dd, J = 11.4 and 5.4 Hz,
1 H), 2.70−76 (m, 1 H), 2.56 (dd, J = 11.4 and 7.2 Hz, 1 H), 2.43 (s, 3
H), 1.10 (d, J = 7.2 Hz, 3 H); 13C NMR (150 MHz, CDCl3) δ 194.4,
163.3, 144.3, 144.0, 134.2, 133.4, 131.8, 130.0, 129.9, 128.0, 113.8,
55.7, 49.1, 44.9, 31.3, 21 0.7, 17.9; IR (KBr, neat) 2918, 2849, 1640,
1598, 1256, 1165, 1091, 1028, 842, 746 cm−1; HRMS (ESI) m/z calcd
for C21H24NO4S (M + H)+ 386.1426, found 386.1421.
(9) Molinaro, C.; Jamison, T. F. J. Am. Chem. Soc. 2003, 125, 8076−
8077.
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Chem. 2013, 78, 10629−10641.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C NMR and HRMS spectra of all new compounds.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(12) (a) Indukuri, K.; Bondalapati, S.; Kotipalli, T.; Gogoi, P.; Saikia,
A. K. Synlett 2012, 23, 233−238. (b) Indukuri, K.; Bondalapati, S.;
Sultana, S.; Saikia, A. K. RSC Adv. 2012, 2, 9398−9402. (c) Chio, F.
K.; Warne, J.; Gough, D.; Penny, M.; Green, S.; Coles, S. J.;
Hursthouse, M. B.; Jones, P.; Hassall, L.; McGuire, T. M.; Dobbs, A. P.
Tetrahedron 2011, 67, 5107−5124. (d) Li, J.; Li, C.-J. Tetrahedron Lett.
AUTHOR INFORMATION
Corresponding Author
*Fax: +91-361-2690762. E-mail: asaikia@iitg.ernet.in.
Notes
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2001, 42, 793−796. (e) Dobbs, A. P.; Martinovic,
2002, 43, 7055−7057. (f) Yadav, J. S.; Rajasekhar, K.; Murty, M. S. R.
Tetrahedron Lett. 2005, 46, 2311−2314. (g) Dobbs, A. P.; Guesne, S. J.
J.; Martinovic, S.; Coles, S. J.; Hursthouse, M. B. J. Org. Chem. 2003,
́
S. Tetrahedron Lett.
The authors declare no competing financial interest.
́
ACKNOWLEDGMENTS
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́
P.G. gratefully acknowledges the Council of Scientific and
Industrial Research (CSIR) New Delhi for her fellowship. The
authors are grateful to the Council of Scientific and Industrial
Research (CSIR), New Delhi for financial support (Grant No.
01/2332/09-EMR-II).
68, 7880−7883. (h) Yadav, J. S.; Borker, P.; Chakravarthy, P. P.;
Reddy, B. V. S.; Sarma, A. V. S.; Basha, S. J.; Balasubramanian, S.;
Gree, R. J. Org. Chem. 2010, 75, 2081−2084. (i) Reddy, B. V. S.;
́
Chaya, D. N.; Yadav, J. S.; Chatterjee, D.; Kunwar, A. C. Tetrahedron
Lett. 2011, 52, 2961−2964.
(13) Sau, M.; Rodríguez-Escrich, C.; Pericas
13, 5044−5047.
̀
, M. A. Org. Lett. 2011,
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