Solvent-free one-pot synthesis of pyrane derivatives

Article abstract of DOI:10.1002/jhet.818

A straightforward and an efficient method for the synthesis of 2H-pyrans via the one-pot, reaction of alkyl bromides, carbon disulfide, secondary amines, activated acetylenes and isocyanides under solvent-free conditions without using any catalyst at room

Full text of DOI:10.1002/jhet.818

March 2012
Solvent-Free One-Pot Synthesis of Pyrane Derivatives
405
Faramarz Rostami-Charati,a* Zinatossadat Hossaini,b
Mohammad A. Khalilzadeh,b Mahboube Islami Moghaddam,c
and Vahid Babaeid
aDepartment of Chemistry, Faculty of Science, Gonbad Kavous University,
PO Box 163, Gonbad, Iran
bDepartment of Chemistry, Islamic Azad University, Qaemshahr Branch, Mazandaran, Iran
cDepartment of Chemistry, University of Payam Noor, Iran
dDepartment of Environmental and Civil Engineering, Babol Noshirvani University of Technology,
Babol, Iran
*E-mail: f_rostami_ch@yahoo.com or frostami@gau.ac.ir
Received September 3, 2010
DOI 10.1002/jhet.818
Published online 10 November 2011 in Wiley Online Library (wileyonlinelibrary.com).
A straightforward and an efficient method for the synthesis of 2H-pyrans via the one-pot, reaction of
alkyl bromides, carbon disulfide, secondary amines, activated acetylenes and isocyanides under solvent-
free conditions without using any catalyst at room temperature is reported. The method offers several
advantages including high yields of products and an easy work-up procedure.
J. Heterocyclic Chem., 49, 405 (2012).
INTRODUCTION
RESULTS AND DISCUSSION
Within the last decade, the resurgence of interest in
multicomponent reactions (MCRs) has been considered,
not only because of their inherent atom efficiency and
ease of implementation, but also because of their value
to the pharmaceutical industry for construction of low
molecular weight compound libraries through combina-
torial strategies or parallel synthesis [1,2]. The capability
of an isonitrile to undergo facile a-addition with a nucle-
ophile and an electrophile under mild conditions made it
a popular reactant for the development of novel MCRs
[3–9]. For the purposes of eco-friendly ‘‘green chemis-
try’’, a reaction should ideally, be conducted under sol-
vent-free conditions with minimal or no side-product
formation and with utmost atom economy [10]. In the
context of our on going studies on heterocyclic con-
struction mediated by zwitterionic intermediates [11],
the possibility of trapping the 1:1 intermediate formed
between dialkyl acetylenedicarboxylate and isocyanides
with suitable CAH acids appeared attractive from the
viewpoint of devising a novel MCR [12]. Here, we
describe an efficient synthesis of 2H-pyran derivatives
via the reaction of alkyl bromides, carbon disulfide, sec-
ondary amines, and activated acetylenes and isocyanides
under solvent-free conditions at room temperature
(Scheme 1).
As indicated in Scheme 1, secondary amines 1, car-
bon disulfide 2, alkyl bromides 3, activated acetylenes
4, and isocyanides 5 undergo a smooth 1:1:1:1:1 addi-
tion reaction under solvent-free conditions at room tem-
perature (the secondary amines and carbon disulfide are
mixed first and then alkyl bromides is added. subse-
quently, activated acetylenes and isocyanides are added)
to produce 2H-pyran derivatives 6 in 90–97% yields
(Scheme 1). Structures of compounds 6a–6l were
1
deduced from their IR, mass, H NMR and 13C NMR
spectra. The mass spectra of these compounds displayed
molecular ion peaks at the appropriate m/z values. The
1H NMR spectrum of 6a exhibited a triplet at d ¼ 1.29
(3J ¼ 7.6 Hz) for the methyl group and four singlets for
the tert-butyl (d 1.27 ppm), methoxy (3.75 and 3.82
ppm), and olefinic (d 6.57 ppm) protons. The proton-
decoupled 13C NMR spectrum of 6a showed 16 distinct
resonances in agreement with the proposed structure.
Three single resonances at d ¼ 160.4, 162.3 and 163.8
ppm are observed in the 13C NMR spectrum of 6a,
which are attributed to the carbonyl groups.
Although we have not established the mechanism of
the reactions in an experimental manner, a possible expla-
nation is proposed in Scheme 2. Dithiocarbamates 7 were
produced from the reaction of secondary amines 1, carbon
C
V
2011 HeteroCorporation

406
F. Rostami-Charati, Z. Hossaini, M. A. Khalilzadeh, M. I. Moghaddam, and V. Babaei
Vol 49
and are uncorrected. 1H NMR and 13C NMR spectra were
obtained with a Bruker FT-500 spectrometer in chloroform-d1,
and tetramethylsilane (TMS) was used as an internal standard.
Mass spectra were recorded with a Finnigan Mat TSQ-70
spectrometer. Infrared (IR) spectra were acquired on a Nicollet
Magna 550-FT spectrometer. Elemental analyses were carried
out with a Perkin-Elmer model 240-C apparatus. The results of
elemental analyses (C, H, N) were within 60.4% of the calcu-
lated values.
Scheme 1
Typical procedure for the preparation of 2H-pyran
derivatives 6. To a mixture of the alkyl bromides (2 mmol)
and carbon disulfide (4 mmol) in the test tube, amine (4
mmol) was added and stirred at 0ꢀC for 30 min, then warmed
to room temperate and stirring was continued until the reaction
was complete (reaction mixture solidified or monitored by
TLC). To this mixture activated acetylenes (2 mmol) was
added. Then, isocyanides (2 mmol) was added slowly and mix-
ture of reaction was stirred for 12 hours. Upon completion that
monitored by TLC, water (15 mL) was poured into the mixture
of reaction. The resulting precipitate was separated by filtration
and was purified with diethyl ether (Et2O) to afford the pure
title compounds.
disulfide 2, and alkyl bromides 3 under solvent-free con-
ditions. On the basis of the well-established chemistry of
isocyanides [12–17], it is reasonable to assume that the
compound 8 apparently results from initial addition of the
isocyanide to the activated acetylenes that adds to dithio-
carbamate 7 resulting in the formation of 9, which under-
goes cyclization to generate the 2H-pyrans 6a–l.
In conclusion, we have developed the most useful and
dependable procedure currently available for the synthe-
sis of 2H-pyrans by using low-cost and readily available
starting materials in one-pot. This method represents a
simple and green procedure, uses mild reaction condi-
tions, and has general applicability.
6-Ethyl 3,4-dimethy-2-(tert-butylimino)-2H-pyran-3,4,6-
tricarboxylate (6a). White powder, mp 124–127ꢀC, yield:
0.64 g (95%). IR (KBr) (mmax/cmꢁ1): 1738, 1732, 1723, 1547
and 1245 cmꢁ1
.
1H NMR: d ¼ 1.27 (9 H, s, Me3C), 1.29 (3
H, t, 3J ¼ 7.6 Hz, Me), 3.75 (3 H, s, MeO), 3.82 (3 H, s,
MeO), 4.32 (2 H, q, 3J ¼ 7.6 Hz, CH2O), 6.57 (1 H, s, CH)
ppm. 13C NMR: d ¼ 14.0 (Me), 29.6 (Me3C), 51.6 (MeO),
52.3 (MeO), 55.3 (CAN), 63.1 (CH2O), 117.4 (CH), 135.4
(C), 143.2 (C), 145.4 (C), 149.8 (C¼¼N), 160.4 (C¼¼O), 162.3
(C¼¼O), 163.8 (C¼¼O) ppm. MS: m/z (%) ¼ 339 (Mþ, 15),
308 (45), 282 (85), 57 (100), 31(86). Anal. Calc. for
C16H21NO7 (339.34): C, 56.63; H, 6.24; N, 4.13 found: C,
56.58; H, 6.12; N, 4.02%.
Triethyl 2-(tert-butylimino)-2H-pyran-3,4,6-tricarboxylate
(6b). Yellow powder, mp 130–132ꢀC. yield: 0.68 g (93%). IR
(KBr) (mmax/cmꢁ1): 1738, 1735, 1724, 1582 and 1195 cmꢁ1
.
3
1H NMR: d ¼ 1.26 (9 H, s, Me3C), 1.29 (3 H, t, J ¼ 7.3 Hz,
EXPERIMENTAL
Me), 1.32 (3 H, t, 3J ¼ 7.3 Hz, Me), 1.36 (3 H, t, 3J ¼ 7.4
3
3
Hz, Me), 4.13 (2 H, q, J ¼ 7.3 Hz, CH2O), 4.15 (2 H, q, J
All chemicals were obtained from commercial sources.
Melting points were measured on a Kofler hot stage apparatus
3
¼ 7.3 Hz, CH2O), 4.24 (2 H, q, J ¼ 7.4 Hz, CH2O), 6.64 (1
Scheme 2
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

March 2012
Solvent-Free One-Pot Synthesis of Pyrane Derivatives
407
H, s, CH) ppm. 13C NMR: d ¼ 13.8 (Me), 14.1 (Me), 14.3
(Me), 30.2 (Me3C), 55.6 (CAN), 62.3 (CH2O), 62.6 (CH2O),
63.0 (CH2O), 119.2 (CH), 136.8 (C), 142.6 (C), 145.4 (C),
148.4 (C¼¼N), 161.5 (C¼¼O), 162.8 (C¼¼O), 163.3 (C¼¼O)
ppm. MS: m/z (%) ¼ 367 (Mþ, 10), 339 (62), 310 (84), 57
(100), 45 (48). Anal. Calc. for C18H25NO7 (367.39): C, 58.85;
H, 6.86; N, 3.81 found: C, 58.78; H, 6.73; N, 3.75%.
6-Ethyl 3,4-dimethy-2-(cyclohexylimino)-2H-pyran-3,4,6-
tricarboxylate (6c). White powder, mp 127–129ꢀC, yield:
0.67 g (92%). IR (KBr) (mmax/cmꢁ1): 1735, 1730, 1722, 1554
Dimethyl 2-(tert-butylimino)-6-(4-nitropheny)l-2H-pyran-
3,4-dicarboxylate (6g). Yellow powder, mp 152–154ꢀC, yield:
0.70 g (90%). IR (KBr) (mmax/cmꢁ1): 1738, 1732, 1545, 1412
and 1175 cmꢁ1
.
H, s, MeO), 3.85 (3 H, s, MeO), 6.48 (1 H, s, CH), 7.87 (2 H,
1H NMR: d ¼ 1.27 (9 H, s, CMe3), 3.80 (3
3
3
d, J ¼ 8.2 Hz, 2 CH), 8.45 (2 H, d, J ¼ 8.2 Hz, 2 CH) ppm.
13C NMR: d ¼ 29.8 (CMe3), 52.0 (MeO), 52.6 (MeO), 56.8
(CAN), 107.6 (CH), 125.2 (2 CH), 129.8 (2 CH), 133.9 (C),
139.7 (C), 142.9 (C), 146.8 (C), 156.4 (C¼¼ C¼¼N), 158.9 (C),
162.4 (C¼¼O), 164.6 (C¼¼O) ppm. MS: m/z (%) ¼ 388 (Mþ,
15), 357 (54), 266 (52), 120 (85), 57 (100), 31(78). Anal.
Calc. for C19H20N2O7 (388.37): C, 58.76; H, 5.19; N, 7.21
found: C, 58.68; H, 5.04; N, 7.14%.
1
3
and 1215 cmꢁ1. H NMR: d ¼ 1.25 (3 H, t, J ¼ 7.5 Hz, Me),
1.32 (2 H, m, CH2), 1.38 (2 H, m, CH2), 1.45 (2 H, m, CH2),
1.67 (2 H, m, CH2), 1.80 (2 H, m, CH2), 3.74 (3 H, s, MeO),
3
3.77 (1 H, m, N-CH), 3.80 (3 H, s, MeO), 4.35 (2 H, q, J ¼
Diethyl
2-(tert-butylimino)-6-(4-nitropheny)l-2H-pyran-
7.5 Hz, CH2O), 6.48 (1 H, s, CH) ppm. 13C NMR: d ¼ 14.1
(Me), 24.2 (CH2), 24.6 (CH2), 25.8 (CH2), 33.5 (CH2), 33.9
(CH2), 52.0 (MeO), 52.5 (MeO), 56.7 (CAN), 63.4 (CH2O),
117.5 (CH), 135.6 (C), 143.4 (C), 145.5 (C), 148.7 (C¼¼N),
161.2 (C¼¼O), 162.4 (C¼¼O), 164.2 (C¼¼O) ppm. Anal. Calc.
for C18H23NO7 (365.38): C, 59.17; H, 6.34; N, 3.83 found: C,
59.02; H, 6.27; N, 3.72%.
3,4-dicarboxylate (6h). Pale yellow powder, mp 154–156ꢀC,
yield: 0.79g (95%). IR (KBr) (mmax/cmꢁ1): 1730, 1727, 1645,
1548 and 1232 cmꢁ1. H NMR: d ¼ 1.27 (9 H, s, CMe3), 1.31
1
(3 H, t, 3J ¼ 7.4 Hz, Me), 1.37 (3 H, t, 3J ¼ 7.3 Hz, Me),
3
3
4.12 (2 H, q, J ¼ 7.4 Hz, CH2O), 4.25 (2 H, q, J ¼ 7.3 Hz,
3
CH2O), 6.45 (1 H, s, CH), 8.05 (2 H, d, J ¼ 8.0 Hz, 2 CH),
8.37 (2 H, d, 3J ¼ 8.0 Hz, 2 CH) ppm. 13C NMR: d ¼ 13.8
(Me), 14.2 (Me), 30.4 (CMe3), 57.0 (CAN), 61.4 (CH2O), 62.6
(CH2O), 107.5 (CH), 126.0 (2 CH), 130.1 (2 CH), 140.2 (C),
141.3 (C), 143.0 (C), 146.5 (C), 157.2 (C¼¼N), 157.6 (C),
162.5 (C¼¼O), 165.3 (C¼¼O) ppm. Anal. Calc. for C21H24N2O7
(416.43): C, 60.57; H, 5.81; N, 6.73 found: C, 60.49; H, 5.75;
N, 6.68%.
6-Ethyl 3,4-dimethy-2-(2-ethoxy-2-oxoethylimino)-2H-py-
ran-3,4,6-tricarboxylate (6d). Pale yellow powder, mp 131–
133ꢀC. yield: 0.68 g (95%). IR (KBr) (mmax/cmꢁ1): 1736,
1
1732, 1725, 1527 and 1159 cmꢁ1. H NMR: d ¼ 1.32 (3 H, t,
3
3J ¼ 7.4 Hz, Me), 1.35 (3 H, t, J ¼ 7.5 Hz, Me), 3.76 (3 H,
s. MeO), 3.82 (3 H, s. MeO), 4.15 (2 H, q, 3J ¼ 7.4 Hz,
3
CH2O), 4.18 (2 H, q, J ¼ 7.4 Hz, CH2O), 4.22 (2 H, s, CH2),
Di(tert-butyl) 2-[cyclohexylimino)-6-phenyl-2H-pyran-3,4-
dicarboxylate (6i). Yellow powder, mp 147–149ꢀC, yield:
0.85 g (94%). IR (KBr) (mmax/cmꢁ1): 1728, 1718, 1654, 1568
6.58 (1 H, s, CH) ppm. 13C NMR: d ¼ 13.7 (Me), 14.0 (Me),
50.8 (CH2-N), 51.7 (MeO), 52.3 (MeO), 61.4 (OCH2), 62.3
(OCH2), 118.7 (CH), 136.5 (C), 142.3 (C), 144.9 (C), 147.8
(C¼¼N), 161.8 (C¼¼O), 162.0 (C¼¼O), 163.2 (C¼¼O), 163.6
(C¼¼O) ppm. Anal. Calc. for C16H19NO9 (369.32): C, 52.03;
H, 5.19; N, 3.79 found: C, 51.97; H, 5.07; N, 3.68%.
1
and 1258 cmꢁ1. H NMR: d ¼ 1.32 (2 H, m, CH2), 1.38 (2 H,
m, CH2), 1.45 (2 H, m, CH2), 1.65 (2 H, m, CH2), 1.67 (9 H,
s,CMe3), 1.71 (9 H, s,CMe3), 1.83 (2 H, m, CH2), 3.75 (1 H,
m, N-CH), 6.48 (1 H, s, CH), 7.68 (2 H, d, 3J ¼ 7.8 Hz, 2
3
CH), 7.92 (2 H, d, J ¼ 7.8 Hz, 2 CH) ppm. 13C NMR: d ¼
Dimethyl
2-[cyclohexylimino)-6-phenyl-2H-pyran-3,4-
dicarboxylate (6e). Yellow powder, mp 135–137ꢀC, yield:
0.72 g (97%). IR (KBr) (mmax/cmꢁ1): 1730, 1725, 1548 and
24.5 (CH2), 24.7 (CH2), 25.8 (CH2), 28.2 (CMe3), 29.4
(CMe3), 34.3 (CH2), 35.0 (CH2), 57.0 (CAN), 79.2 (CMe3),
82.3 (CMe3), 108.3 (CH), 125.6 (2 CH), 129.8 (2 CH), 135.8
(C), 138.5 (C), 142.0 (C), 148.3 (C), 154.8 (C¼¼N), 159.2 (C),
163.4 (C¼¼O), 165.7 (C¼¼O) ppm. Anal. Calc. for C27H33NO5
(453.58): C, 71.50; H, 7.78; N, 3.09 found: C, 71.45; H, 7.70;
N, 2.98%.
1278 cmꢁ1. H NMR: d ¼ 1.34 (2 H, m, CH2), 1.40 (2 H, m,
1
CH2), 1.47 (2 H, m, CH2), 1.66 (2 H, m, CH2), 1.84 (2 H, m,
CH2), 3.75 (3 H, s, MeO), 3.79 (1 H, m, N-CH), 3.82 (3 H, s,
MeO), 6.68 (1 H, s, CH), 7.16 (2 H, t, 3J ¼ 7.2 Hz, 2 CH),
3
3
7.30 (1 H, t, J ¼ 7.5 Hz, CH), 7.63 (2 H, d, J ¼ 7.4 Hz, 2
CH) ppm. 13C NMR: d ¼ 24.3 (CH2), 24.5 (CH2), 25.5 (CH2),
33.3 (CH2), 33.5 (CH2), 51.5 (3 H, s, Me), 52.4 (3 H, s, Me),
56.9 (CAN), 105.8 (CH), 128.3 (2 CH), 129.5 (2 CH), 131.5
(CH), 134.0 (C), 136.4 (C), 140.6 (C), 155.2 (C¼¼N), 158.6
(C), 163.5 (C¼¼O), 165.9 (C¼¼O) ppm. Anal. Calc. for
C21H23NO5 (369.41): C, 68.28; H, 6.28; N, 3.79 found: C,
68.32; H, 6.37; N, 3.84%.
6-Ethyl
3,4-dimethy-2-(1,1,3,3-tetramethylbutylimino)-
2H-pyran-3,4,6-tricarboxylate (6j). Yellow powder, mp 137–
139ꢀC, yield: 0.73 g (92%). IR (KBr) (mmax/cmꢁ1): 1730,
1722, 1720, 1545, 1425 and 1167 cmꢁ1
.
1H NMR: d ¼ 1.03
3
(9 H, s, CMe3), 1.24 (3 H, t, J ¼ 7.3 Hz, Me), 1.55 (3 H, s,
Me), 1.56 (3 H, s, Me), 1.83 (2 H, s, CH2), 3.74 (3 H, s,
MeO), 3.82 (3 H, s, MeO), 4.23 (2 H, q, 3J ¼ 7.3 Hz, Me),
6.84 (1 H, s, CH) ppm. 13C NMR: d ¼ 13.9 (Me), 29.7 (C),
29.8 (Me), 31.6 (CMe3), 31.9 (Me), 51.5 (MeO), 52.7 (MeO),
55.0 (CH2), 59.2 (CAN), 61.2 (CH2O), 109.4 (CH), 139.0
(C), 141.3 (C), 144.5 (C), 158.4 (C), 160.2 (C¼¼O), 161.3
(C¼¼O), 163.5 (C¼¼O) ppm. Anal. Calc. for C20H29NO7
(395.45): C, 60.75; H, 7.39; N, 3.54 found: C, 60.68; H, 7.32;
N, 3.43%.
Dimethyl 2-(tert-butylimino)-6-(4-methylpheny)l-2H-py-
ran-3,4-dicarboxylate (6f). Pale yellow powder, mp 143–
145ꢀC, yield: 0.67 g (94%). IR (KBr) (mmax/cmꢁ1): 1732,
1
1725, 1557, 1410 and 1127 cmꢁ1. H NMR: d ¼ 1.25 (9 H, s,
CMe3), 2.35 (3 H, s, Me), 3.78 (3 H, s, MeO), 3.83 (3 H, s,
MeO), 6.42 (1 H, s, CH), 7.42 (2 H, d, 3J ¼ 7.6 Hz, 2 CH),
7.84 (2 H, d, 3J ¼ 7.6 Hz, 2 CH) ppm. 13C NMR: d ¼ 21.7
(Me), 30.6 (CMe3), 51.6 (MeO), 52.4 (MeO), 57.2 (CAN),
108.6 (CH), 125.7 (2 CH), 129.3 (2 CH), 133.2 (C), 134.5 (C),
137.0 (C), 142.4 (C), 155.2 (C¼¼N), 156.8 (C), 163.8 (C¼¼O),
164.7 (C¼¼O) ppm. Anal. Calc. for C20H23NO5 (357.40): C,
67.21; H, 6.49; N, 3.92 found: C, 67.18; H, 6.53; N, 4.02%.
Dimethyl 2-(2-ethoxy-2-oxoethylimino)-6-(4-methylphenyl)-
2H-pyran-3,4-dicarboxylate (6k). White powder, mp 138–
140ꢀC, yield: 0.70 g (90%). IR (KBr) (mmax/cmꢁ1): 1738,
1
1730, 1728, 1624, 1557, 1410 and 1127 cmꢁ1. H NMR: d ¼
3
1.30 (3 H, t, J ¼ 7.2 Hz, Me), 2.35 (3 H, s, Me), 3.76 (3 H,
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F. Rostami-Charati, Z. Hossaini, M. A. Khalilzadeh, M. I. Moghaddam, and V. Babaei
Vol 49
s, MeO), 3.83 (3 H, s, MeO), 4.20 (2 H, s, CH2), 4.28 (2 H, q,
3
C21H23NO7 (401.41): C, 62.84; H, 5.78; N, 3.49 found: C,
62.75; H, 5.69; N, 3.38%.
3J ¼ 7.2 Hz, OCH2), 6.47 (1 H, s, CH), 7.54 (2 H, d, J ¼ 7.5
3
Hz, 2 CH), 7.85 (2 H, d, J ¼ 7.6 Hz, 2 CH) ppm. 13C NMR:
d ¼ 14.1 (Me), 21.4 (Me), 50.3 (CH2-N), 51.6 (MeO), 52.4
(MeO), 61.3 (OCH2), 107.4 (CH), 126.3 (2 CH), 129.7 (2
CH), 134.8 (C), 135.2 (C), 137.3 (C), 142.8 (C), 153.6 (C),
156.5 (C¼¼N), 160.2 (C¼¼O), 162.7 (C¼¼O), 164.3 (C¼¼O)
ppm. Anal. Calc. for C20H21NO7 (387.39): C, 62.01; H, 5.46;
N, 3.62 found: C, 61.96; H, 5.38; N, 3.54%.
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Diethyl 2-(2-ethoxy-2-oxoethylimino)-6-phenyl-2H-pyran-
3,4-dicarboxylate (6l). White powder, mp 144–146ꢀC, yield:
0.75 g (93%). IR (KBr) (mmax/cmꢁ1): 1732, 1728, 1725, 1612,
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1
3
1547, 1385 and 1215 cmꢁ1. H NMR: d ¼ 1.23 (3 H, t, J ¼
3
3
7.4 Hz, Me), 1.26 (3 H, t, J ¼ 7.5 Hz, Me), 1.29 (3 H, t, J
3
¼ 7.3 Hz, Me), 4.12 (2 H, q, J ¼ 7.4 Hz, OCH2), 4.15 (2 H,
3
3
q, J ¼ 7.5 Hz, OCH2), 4.18 (2 H, s, CH2), 4.20 (2 H, q, J ¼
¨
[8] Jacobi von Wangelin, A.; Neumann, H.; Gordes, D.; Klaus,
3
7.5 Hz, OCH2), 6.52 (1 H, s, CH), 7.21 (2 H, t, J ¼ 7.8 Hz, 2
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CH), 7.42 (1 H, t, 3J ¼ 7.6 Hz, CH), 7.79 (2 H, t, 3J ¼ 7.6
Hz, 2 CH) ppm. 13C NMR: d ¼ 13.8 (Me), 14.0 (Me), 14.3
(Me), 52.4 (CH2-N), 60.3 (OCH2), 61.5 (OCH2), 62.0 (OCH2),
108.0 (CH), 128.2 (2 CH), 129.5 (2 CH), 131.4 (CH), 135.0
(C), 135.8 (C), 142.3 (C), 154.8 (C), 158.5 (C¼¼N), 162.3
(C¼¼O), 163.5 (C¼¼O), 164.8 (C¼¼O) ppm. Anal. Calc. for
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deh, H. R. Tetrahedron 2003, 59, 6083.
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet