A simple and efficient procedure for synthesis of optically active 1,2,4-Triazolo-[3,4-b]-1,3,4-thiadiazole derivatives containing l-amino acid moieties

Article abstract of DOI:10.1002/jccs.200900151

Some new and optically active 1,2,4-triazolo thiadiazoles bearing N-phthaloyl-L-amino acids were synthesized by reaction of 4-amino-5-(3-or 4-)pyridyl-3-mercapto-(4H)-1,2,4-triazoles with N-phthaloyl-L-amino acids in the presence of phosphorus oxychloride. All the newly synthesized compounds were confirmed by IR, ¹HNMR, ¹³C NMR and elemental analysis.

Full text of DOI:10.1002/jccs.200900151

Journal of the Chinese Chemical Society, 2009, 56, 1043-1047
1043
A Simple and Efficient Procedure for Synthesis of Optically Active
1,2,4-Triazolo-[3,4-b]-1,3,4-thiadiazole Derivatives Containing L-Amino
Acid Moieties
Naser Foroughifar,* Akbar Mobinikhaledi, Sattar Ebrahimi,
Mohammad Ali Bodaghi Fard and Hassan Moghanian
Department of Chemistry, Faculty of Science, Arak University, Arak 38156-879, Iran
Some new and optically active 1,2,4-triazolo thiadiazoles bearing N-phthaloyl-L-amino acids were
synthesized by reaction of 4-amino-5-(3- or 4-)pyridyl-3-mercapto-(4H)-1,2,4-triazoles with N-phth-
aloyl-L-amino acids in the presence of phosphorus oxychloride. All the newly synthesized compounds
were confirmed by IR, 1H NMR, 13C NMR and elemental analysis.
Keywords: L-Amino acid; 1,2,4-Triazole-3-thiol; Triazolothiadiazole.
INTRODUCTION
containing L-amino acids.
The recent literature is enriched with progressive
findings about the synthesis and pharmacological activity
of fused heterocycles. Heterocycles bearing a triazole or
1,3,4-thiadiazole moiety are reported to show biological
properties such as antibacterial,1 anti aggregatory agent,2
antiviral3 and anti-inflammatory4 activities. In addition, the
N-bridged heterocycles derived from 1,2,4-triazoles have
applications in the field of medicine, agriculture and indus-
try.5 1,3,4-Thiadiazoles exhibit broad spectrum of biologi-
cal activities, possibly due to the presence of toxophoric
N-C-S moiety.6 They found applications as antibacterial,
antitumor, anti-inflammatory agents, pesticides, herbicides,
dyes, lubricants and analytical reagents.7 The [1,2,4]-tri-
azolo-[3,4-b]-[1,3,4]-thiadiazole derivatives obtained by
fusing the biolibale [1,2,4]-triazole and [1,3,4]-thiadiazole
ring together, are reported to possess antibacterial, anti-
fungal, CNS depressant, antiviral, analgesic and plant
growth regulatory effects.8 A literature search revealed
which the preparation of these compounds have been ex-
tensively studied in the recent years, as followed from data
of the most convenient procedure for the synthesis of
[1,2,4]-triazolo-[3,4-b]-[1,3,4]-thiadiazole derivatives is
based on the reaction of 5-substituted 4-amino-(4H)-1,2,4-
triazole-3-thioles with carboxylic acids.9-12 Nevertheless,
to date there have been no report that produces the optically
active 1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazole ring systems
We report herein the reaction of 4-amino-5-aryl-3-
mercapto-(4H)-1,2,4-triazoles with N-phthaloyl-L-amino
acids in presence of phosphorus oxychloride (POCl3) to
give optically active 1,2,4-triazolo-[3,4-b]-1,3,4-thiadia-
zoles with the hope to obtain compounds with better bio-
logical activities, because chirality is a fundamental prop-
erty of the biological molecules and recognition phenom-
ena associated with these compounds. Phosphorus oxy-
chloride was necessary for this condensation, which acti-
vate the carboxyl group of amino acids and increases its
electrophilicity to enhance the addition of triazole to it.
RESULTS AND DISCUSSION
N-phthaloyl-L-amino acids 4a-e was chosen as start-
ing material as described by Hoffmann and Shenmav.13
Aroyl hydrazides 1a-b were reacted with carbon disulfide
and potassium hydroxide in methanol to yield dithiocar-
bazinates 2a-b in high yield which later cyclized to 5-sub-
stituted 4-amino-(4H)-1,2,4-triazole-3-thioles 3a-b by re-
acting with hydrazine hydrate. The resultant triazoles 3a-b
were further converted to 1,2,4-triazolo-[3,4-b]-1,3,4-thia-
diazoles 5a-j through one pot reaction by condensation
with N-phthaloyl-L-amino acids 4a-e in the presence of
POCl3 as outlined in Scheme I. This procedure afforded
various triazolo thiadiazoles in 52-80% yields. The struc-
ture of 5a was confirmed by IR, 1H NMR and 13C NMR.
* Corresponding author. Tel: +98-861-4173402; Fax: +98-861-4173406; E-mail: n_foroughifar@yahoo.com

1044 J. Chin. Chem. Soc., Vol. 56, No. 5, 2009
Foroughifar et al.
Scheme I
The IR spectrum of 5a exhibited absorption bands at 3084
cm-1 due to aromatic CH, 1776 and 1707 cm-1 due to C=O
for imide’s carbonyl groups. Additional support for the
structure of 5a was obtained by recording its 1H NMR spec-
trum, which exhibited a singlet at d 5.3 due to NCH2 pro-
tons, two doublets at d 8.7, 8.0 and multiplet at d 7.92-7.98,
integrating for eight aromatic protons.
useful for combinational syntheses of type 5 compounds
having various R substitutions with a view to test for bio-
logical activity.
EXPERIMENTAL SECTION
Melting points were determined using an electro ther-
mal digital apparatus and are uncorrected. Purity of the
compound was checked by thin layer chromatography
(TLC) using EtOH/n-hexane (1:1 v/v) as an eluent. IR
spectra were prepared on a galaxy series FT-IR 5000 spec-
trophotometer using KBr discs. 1H NMR spectra were re-
corded on Bruker spectrophotometer (300 MHz) in DMSO-
d6 or CDCl3 using TMS as an internal standard. Specific ro-
tations were measured by using an A-Kruse polarimeter. C,
H, N and S analyses were performed on a Vario EL III ele-
mental analyzer.
The infrared spectra of the triazole 3a-b showed two
absorption bands, at 2728 cm-1 and 3230-3400 cm-1 due to
SH and NH2 groups which were absent in the IR spectra of
the triazolo thiadiazoles 5a-j. Similarly the 1H NMR spec-
tra of the compounds 3a-b showed two characteristic ab-
sorption (broad singlet at d 5.9) that was attributed to the
NH2 group, and another at d 14.2, was assigned to the SH,
which were disappeared by the formation of the triazolo
thiadiazoles. The absence of these absorptions due to the
SH and NH2 groups of triazoles established that all the tri-
azoles had converted to triazolo thiadiazoles by reacting
with the COOH groups of the various N-phthaloyl-L-amino
acids. The IR, 1H NMR, 13C NMR and elemental analysis
supported the structure of various synthesized optically ac-
tive triazolo thiadiazoles.
General procedure for preparation of compound 3a-b
Pyridyl acid hydrazid 1a-b (0.07 mol) was treated
with a solution of potassium hydroxide (0.11 mol) in meth-
anol (50 mL) at 0-5 °C whilst stirring. Then 0.11 mol of car-
bon disulfide was added slowly and the reaction mixture
was stirred for overnight at room temperature. The solid
product 2a-b was filtered, washed with diethyl ether and
dried. It was directly used for next step without purifica-
tion. A suspension of potassium dithiocarbazinate 2a-b in
water (20 mL) and excess amount of hydrazine hydrate was
refluxed for 20 h with occasional shaking. The color of the
reaction mixture changed to green with the evolution of the
CONCLUSIONS
We have shown that reaction of 5-substituted 4-ami-
no-(4H)-1,2,4-triazole-3-thioles with N-phthaloyl-L-ami-
no acids on heating in POCl3 involve cyclization with for-
mation of 1,3,4-thiadiazole rings. This reaction may be

Synthesis of Optically Active Triazolothiadiazoles
J. Chin. Chem. Soc., Vol. 56, No. 5, 2009 1045
hydrogen sulfide gas. A homogeneous reaction mixture
was obtained during the reaction process. It was cooled to
room temperature and diluted with water (20 mL) and acid-
ified with concentrated hydrochloric acid. The white pre-
cipitate was filtered, washed with cold water and recrystal-
lized from aqueous ethanol.
207 °C; IR (KBr) n: 3051 (aromatic CH stretch.), 1778,
1712 (C=O), 1606 (C=N), 1550, 1492 (C=C ring stretch.)
1
cm-1. H NMR (300 MHz, DMSO-d6) d: 8.78 (d, J = 5.7
Hz, 2H), 8.08 (d, J = 5.8 Hz, 2H), 7.87-7.95 (m, 4H), 5.93
(q, J = 7.1 Hz, 1H, N-CH), 1.96 (d, J = 7.1 Hz, 3H, CH3).
13C NMR (75 MHz, DMSO-d6) d: 17.1, 46.9, 119.6,
123.9, 131.6, 132.5, 135.3, 143.7, 151.1, 156.4, 167.4,
171.5. Anal. Calcd. for C18H12N6O2S: C, 57.44; H, 3.21;
N, 22.23; S, 8.52. Found: C, 57.26; H, 3.18; N, 22.17; S,
8.56.
4-Amino-5-(4-pyridyl)-1,2,4-triazole-3-thiol (3a)
Yield 85%, mp 260 °C (lit.14 mp 259-261 °C).
4-Amino-5-(3-pyridyl)-1,2,4-triazole-3-thiol (3b)
Yield 52%, mp 210 °C (dec.) [(lit.15 mp 208 °C
(dec.)].
(S)-(+)-6-[2-(Isoindolin-1,3-dione)ethyl]-3-(3-pyridyl)-
General procedure for preparation of compound 5a-j
A mixture of triazole 3a-c (1 mmol), N-phthaloyl-L-
amino acid 4a-e (1 mmol) in POCl3 (7 mL) was refluxed
for 16 h. The reaction mixture slowly was poured into
crashed ice with stirring and neutralized with solid potas-
sium bicarbonate. The mixture was allowed to stand over-
night and the solid separated out was filtered and washed
with cold water. The compound so obtained was dried and
crystallized from appropriate solvent, giving the pure
products 5a-j.
1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazole (5d)
[a] 2D2 = -111 (c = 0.2, DMSO), Yield 72%, mp 204-
206 °C; IR (KBr) n: 3090 (aromatic CH stretch.), 1774,
1709 (C=O), 1604 (C=N), 1574, 1477 (C=C ring stretch.)
cm-1. 1H NMR (300 MHz, DMSO-d6) d: 9.38 (s, 1H), 8.89
(d, J = 4.8 Hz, 1H), 8.04 (br, 1H), 7.85-7.91 (m, 4H),
7.60-7.64 (m, 1H), 5.90 (q, J = 7.0 Hz, 1H, N-CH), 1.94 (d,
J = 7.0 Hz, 3H, CH3). 13C NMR (75 MHz, DMSO-d6) d:
17.1, 46.7, 121.7, 124.1, 124.8, 131.8, 133.0, 136.4, 143.8,
146.9, 151.6, 156.7, 167.8, 171.3. Anal. Calcd. for
C18H12N6O2S: C, 57.44; H, 3.21; N, 22.23; S, 8.52. Found:
C, 57.22; H, 3.17; N, 22.19; S, 8.55.
6-[2-(Isoindolin-1,3-dione)methyl]-3-(4-pyridyl)-1,2,4-
triazolo-[3,4-b]-1,3,4-thiadiazole (5a)
Yield 70%, mp 290-292 °C; IR (KBr) n: 3084 (aro-
matic CH stretch.), 1776, 1707 (C=O), 1607 (C=N), 1527,
1469 (C=C ring stretch.) cm-1. 1H NMR (300 MHz, DMSO-
d6) d: 8.79 (d, J = 5.8 Hz, 2H), 8.08 (br, 2H), 7.92-7.98 (m,
4H), 5.26 (s, 2H, N-CH2). Anal. Calcd. for C17H10N6O2S:
C, 56.35; H, 2.78; N, 23.19; S, 8.85. Found: C, 56.14; H,
2.75; N, 23.13; S, 8.81.
(S)-(-)-6-[2-(Isoindolin-1,3-dione)phenylethyl]-3-(4-pyr-
idyl)-1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazole (5e)
[a] 2D2 = -302 (c = 0.2, DMSO), Yield 80%, mp 231-
233 °C; IR (KBr) n: 3095 (aromatic CH stretch.), 1778,
1710 (C=O), 1604 (C=N), 1530, 1444 (C=C ring stretch.)
cm-1. 1H NMR (300 MHz, DMSO-d6) d: 8.79 (br, 2H), 8.10
(d, J = 4.1 Hz, 2H), 7.84-7.89 (m, 4H), 7.13-7.30 (m, 5H),
6.12-6.17 (dd, J = 9.0, 7.3 Hz, 1H, N-CH), 3.78-3.81 (m,
2H, CH2). 13C NMR (75 MHz, DMSO-d6) d: 36.3, 52.7,
119.7, 124.1, 127.6, 129.0, 129.4, 131.1, 132.6, 135.6,
136.2, 143.8, 151.1, 156.4, 167.4, 169.8. Anal. Calcd. for
C24H16N6O2S: C, 63.70; H, 3.56; N, 18.57; S, 7.09. Found:
C, 63.52; H, 3.51; N, 18.49; S, 7.15.
6-[2-(Isoindolin-1,3-dione)methyl]-3-(3-pyridyl)-1,2,4-
triazolo-[3,4-b]-1,3,4-thiadiazole (5b)
Yield 65%, mp 283-284 °C; IR (KBr) n: 3080 (aro-
matic CH stretch.), 1770, 1710 (C=O), 1605 (C=N), 1570,
1467 (C=C ring stretch.) cm-1. 1H NMR (300 MHz, CDCl3)
d: 9.30 (s, 1H), 8.72 (br, 1H.), 8.48 (d, J = 7.9 Hz, 1H),
7.90-7.99 (m, 4H), 7.61-7.65 (dd, J = 7.8, 4.6 Hz, 1H), 5.26
(s, 2H, N-CH2). 13C NMR (75 MHz, CDCl3) d: 45.4, 121.9,
124.1, 124.7, 131.5, 133.0, 134.9, 143.9, 146.9, 150.1,
156.7, 167.8, 168.4. Anal. Calcd. for C17H10N6O2S: C,
56.35; H, 2.78; N, 23.19; S, 8.85. Found: C, 56.42; H, 2.74;
N, 23.09; S, 8.83.
(S)-(-)-6-[2-(Isoindolin-1,3-dione)phenylethyl]-3-(3-pyr-
idyl)-1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazole (5f)
[a] 2D2 = -150 (c = 0.2, DMSO), Yield 80%, mp 221-
222 °C; IR (KBr) n: 3070 (aromatic CH stretch.), 1778,
1710 (C=O), 1604 (C=N), 1550, 1467 (C=C ring stretch.)
cm-1. 1H NMR (300 MHz, DMSO-d6) d: 9.34 (s, 1H), 8.75
(br, 1H), 8.50 (d, J = 7.0 Hz, 1H), 7.84-7.90 (m, 4H), 7.65
(br, 1H), 7.15-7.27 (m, 5H), 6.10-6.16 (dd, J = 8.9, 7.3, 1H,
N-CH), 3.10-3.18 (m, 2H, CH2). 13C NMR (300 MHz,
(S)-(+)-6-[2-(Isoindolin-1,3-dione)ethyl]-3-(4-pyridyl)-
1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazole (5c)
[a] 2D2 = -198 (c = 0.2, DMSO), Yield 75%, mp 206-

1046 J. Chin. Chem. Soc., Vol. 56, No. 5, 2009
Foroughifar et al.
DMSO-d6) d: 36.2, 52.5, 122.1, 124.1, 124.7, 127.6, 128.9,
129.4, 131.0, 133.6, 135.6, 136.2, 143.7, 146.9, 151.5,
156.1, 167.4, 169.4. Anal. Calcd. for C24H16N6O2S: C,
63.70; H, 3.56; N, 18.57; S, 7.09. Found: C, 63.51; H, 3.54;
N, 18.49; S, 7.13.
134.9, 144.1, 150.0, 156.1, 167.3, 169.9. Anal. Calcd. for
C21H18N6O2S: C, 60.27; H, 4.34; N, 20.08; S, 7.66. Found:
C, 60.14; H, 4.31; N, 20.01; S, 7.62.
(S)-6-[2-(Isoindolin-1,3-dione)isopentyl]-3-(3-pyridyl)-
1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazole (5j)
(S)-(+)-6-[2-(Isoindolin-1,3-dione)isobutyl]-3-(4-pyr-
idyl)-1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazole (5g)
[a] 2D2 = -150 (c = 0.2, CHCl3) Yield 58%, mp 218-
219 °C; IR (KBr) n: 3070 (aromatic CH stretch.), 1782,
1710 (C=O), 1606 (C=N), 1550, 1444 (C=C ring stretch.)
[a] 2D2 = -107 (c = 0.2, CHCl3) Yield 65%, mp 172-174
°C; IR (KBr) n: 3055 (aromatic CH stretch.), 1774, 1707
(C=O), 1605 (C=N), 1556, 1456 (C=C ring stretch.) cm-1.
1H NMR (300 MHz, CDCl3) d: 9.40 (s, 1H), 8.60 (br, 1H),
8.46 (br, 1H), 7.72-7.80 (m, 4H), 7.37 (br, 1H), 5.78 (dd, J
= 10.7, 5.4 Hz, 1H, N-CH), 2.54 (br, 1H, CH), 2.07 (br, 1H,
CH2), 1.52 (br, 1H, CH2), 0.93 (br, 6H, 2CH3). 13C NMR
(75 MHz, CDCl3) d: 21.4, 22.8, 25.0, 39.4, 49.7, 121.9,
123.8, 123.9, 131.1, 133.5, 134.8, 143.9, 146.9, 150.7,
155.3, 167.2, 169.5. Anal. Calcd. for C21H18N6O2S: C,
60.27; H, 4.34; N, 20.08; S, 7.66. Found: C, 60.19; H, 4.33;
N, 20.05; S, 7.64.
1
cm-1. H NMR (300 MHz, CDCl3) d: 8.86 (br, 2H), 8.52
(d, J = 5.8 Hz, 2H), 7.81-7.95 (m, 4H), 5.46 (d, 1H, N-CH,
J = 11.4 Hz), 3.1-3.18 (m, 1H, CH, 2H), 1.12 (d, J = 6.6
Hz, 3H, CH3), 1.06 (d, J = 6.5 Hz, 3H, CH3). 13C NMR
(300 MHz, CDCl3) d: 19.4, 20.1, 29.7, 58.2, 119.9, 124.0,
131.0, 133.2, 134.9, 143.9, 149.9, 156.7, 167.4, 168.4.
Anal. Calcd. for C20H16N6O2S: C, 59.39; H, 3.99; N,
20.78; S, 7.93. Found: C, 59.12; H, 3.98; N, 20.63; S,
7.95.
ACKNOWLEDGMENT
(S)-(+)-6-[2-(Isoindolin-1,3-dione)isobutyl]-3-(3-pyr-
idyl)-1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazole (5h)
[a] 2D2 = -125 (c = 0.2, CHCl3), Yield 65%, mp 210-
211 °C; IR (KBr) n: 3070 (aromatic CH stretch.), 1768,
1712 (C=O), 1601 (C=N), 1540, 1429 (C=C ring stretch.)
cm-1. 1H NMR (300 MHz, CDCl3) d: 9.33 (s, 1H), 8.73 (d,
J = 4.1 Hz, 1H), 8.48 (d, J = 7.7 Hz, 1H), 7.86-7.95 (m,
4H), 7.63-7.67 (dd, J = 7.9, 4.9 Hz, 1H), 5.32 (d, J = 11.2
Hz, 1H, N-CH), 2.96-3.04 (m, 1H, CH), 1.06 (d, J = 6.5 Hz,
3H, CH3), 0.96 (d, J = 6.4 Hz, 3H, CH3). 13C NMR (75
MHz, CDCl3) d: 19.5, 20.0, 29.6, 57.9, 122.2, 124.1, 124.6,
131.3, 133.5, 135.5, 143.6, 146.9, 151.4, 156.1, 167.8,
168.1. Anal. Calcd. for C20H16N6O2S: C, 59.39; H, 3.99;
N, 20.78; S, 7.93. Found: C, 59.22; H, 3.98; N, 20.64; S,
7.90.
We gratefully acknowledge the financial support
from the Research Council of the Arak University.
Received December 2, 2008.
REFERENCES
1. Farghaly, A.-A. H. J. Chin. Chem. Soc. 2004, 51, 147.
2. Czarnocka, J.-A.; Foks, H.; Nasal, A.; Petrusewicz, J.;
Damasiewicz, B.; Radwanska, A.; Kaliszan, R. Pharmazie
1991, 46, 109.
3. Srivastava, J.; Swarup, S.; Saxena, V.-K.; Chowdhury, B.-L.
J. Indian Chem. Soc. 1991, 68, 103.
4. Unangst, P.-C.; Shrum, G.-P.; Connor, D.-T.; Dyer, R.-D.;
Schrier, D.-J. J. Med. Chem. 1992, 35, 3691.
5. Farghaly, A.-R.; De Clercq, E.-D.; El-Kashef, H. Arkivoc
2006, 10, 137.
6. Omar, A.-M. M. E.; Aboulwafa, O.-M. J. Heterocycl. Chem.
1986, 23, 1339.
(S)-6-[2-(Isoindolin-1,3-dione)isopentyl]-3-(4-pyridyl)-
1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazole (5i)
[a] 2D2 = -156 (c = 0.2, CHCl3), Yield 52%, mp 187-
188 °C; IR (KBr) n: 3086 (aromatic CH stretch.), 1774,
1712 (C=O), 1602 (C=N), 1530, 1444 (C=C ring stretch.)
cm-1. 1H NMR (300 MHz, CDCl3) d: 8.77 (d, J = 5.8 Hz,
2H), 8.18 (d, J = 5.9 Hz, 2H), 7.78-7.92 (m, 4H), 5.87 (dd, J
= 10.5, 5.6 Hz, 1H, N-CH), 2.61-2.66 (m, 1H, CH), 2.11-
2.14 (m, 1H, CH2), 1.57-1.60 (m, 1H, CH2), 0.96-1.02 (2d,
J = 2.0, 1.9 Hz, 6H, 2 ´ CH3). 13C NMR (75 MHz, CDCl3)
d: 21.5, 22.8, 25.1, 39.6, 49.9, 119.9, 124.0, 131.2, 133.1
7. Kurtzer, F.; Katritzky, A.-R.; Boulton, A.-J. Advances in
Heterocyclic Chemistry; Academic Press: New York, 1965;
Vol. 5, p 165.
8. (a) Hui, X.-P.; Zhang, L.-M.; Zhang, Z.-Y.; Wang, Q.; Wang,
F. J. Chin. Chem. Soc. 2000, 47, 535. (b) Abdallah, M.-A.;
Riyadh, S.-M.; Abbas, I.-M. S.; Gomha, M. J. Chin. Chem.
Soc. 2005, 52, 987. (c) Zhang, Z.-Y.; Sun, X.-W. Hetero-
cycles 1986, 48, 561.
9. Dong, H.-S.; Wang, B. J. Chin. Chem. Soc. 2005, 52, 103.
10. El-Khawass, S.-M.; Habib, N.-S.; Fu, H. J. Heterocycl.

Synthesis of Optically Active Triazolothiadiazoles
J. Chin. Chem. Soc., Vol. 56, No. 5, 2009 1047
Chem. 1989, 26, 177.
Ganguly, N. J. Indian Chem. Soc. 1990, 67, 220. (c) Pandeya,
S.-N.; Sriram, D.; Nath, G.; De Clercq, E. Arzneimittel
Forschung 2000, 50, 55. (d) Joshi, S.-S.; Karnik, A.-V. In-
dian J. Chem., Sect. B: Org. Chem. Incl. Med. Chem. 2006,
45, 1057.
11. Li, D.; Long, D. Synth. Commun. 2005, 35, 2495.
12. Subrahmanya Bhat, K.; Jagadeesh Prasad, D.; Poojary, B.;
Shivarama Holla, B. Phosphorus, Sulfur Silicon Relat.
Elem. 2004, 179, 1595.
13. Hoffmann, E.; Schiff-Shenmav, H. J. Org. Chem. 1962, 27,
4686.
15. (a) Khalil, N.-S. A. M. Carbohydr. Res. 2006, 341, 2187. (b)
Sasaki, T.; Ito, E. J. Heterocycl. Chem. 1981, 18, 1353. (c)
Li, D.; Long, D.; Fu, H. Phosphorus, Sulfur Silicon Relat.
Elem. 2006, 181, 519.
14. (a) Reid, R.-J.; Heindel, D.-N. J. Heterocycl. Chem. 1976,
13, 925. (b) Chande, M.-S.; Karnik, B.-M.; Inamdar, A.-N.;