Synthesis of new guanidium-meldrum acid zwitterionic salts and dynamic NMR study of rotational energy barrier around C-NH bond of guanidine moiety

Article abstract of DOI:10.13005/ojc/300439

Synthesis of the Guanidium-Meldrum acid zwitterionic salts was developed through a three component reaction of 2, 2-dimethyl-1, 3-dioxane-4, 6-dione (Meldrum acid), aromatic aldehydes and N, N, N', N'- Tetramethyl-guanidine in benzen at room temperature.

Full text of DOI:10.13005/ojc/300439

ISSN: 0970-020 X
CODEN: OJCHEG
2014, Vol. 30, No. (4):
Pg. 1791-1797
ORIENTAL JOURNAL OF CHEMISTRY
An International Open Free Access, Peer Reviewed Research Journal
www.orientjchem.org
Synthesis of New Guanidium-Meldrum Acid Zwitterionic
Salts and Dynamic NMR Study of Rotational Energy Barrier
Around C-NH bond of Guanidine Moiety
ALI AMINKHANI
Department of Chemistry, Khoy Branch, Islamic Azad University, Khoy, Iran
*Corresponding author E-mail: ali_aminkhani@yahoo.com
http://dx.doi.org/10.13005/ojc/300439
(Received: May 15, 2014; Accepted: July 23, 2014)
ABSTRACT
Synthesis of the Guanidium-Meldrum acid zwitterionic salts was developed through a
three component reaction of 2, 2-dimethyl-1, 3-dioxane-4, 6-dione (Meldrum acid), aromatic
aldehydes and N, N, N’, N’-Tetramethyl-guanidine in benzen at room temperature. These reaction
conditions allow the preparation of stable zwitterionic salts in good yields. A dynamic NMR effect
is observed as a result of restricted rotation around the C-NH bond in the 1H NMR spectra of these
compounds. The free-energy of activation (G#) for this process is 66 2 kJmol-1 for 4b.
Key words: Benzaldehydes, Dynamic NMR, Meldrum acid, Michael addition,
N, N, N’, N’-Tetramethyl-guanidine, Zwitterionic salts.
INTRODUCTION
salts using three component reaction. The
zwitterions are often as an intermediate species in
some reactions. 8-10 we now describe the synthesis
zwitterionic salts by means of a reaction of N, N, N’,
N’-Tetramethyl-guanidine with conjugated
electrophilic heterodienes. Dynamic NMR provides
important kinetic data and affords good information
in this matter on a dynamic process, when
discussing the barrier separating two states that
The Knoevenagel condensation of
Meldrum acid with aromatic aldehydes with the aim
of forming a carbon-carbon double bond is a well-
documented reaction1 that carried out using various
conditions. Arylidene Meldrum acids are useful
reactive intermediates, being susceptible to 1, 4-
2
3
addition, in Diels-Alder reactions acting as
4
11
activated dienophiles
and preparation of
are observable by NMR spectroscopy. Thus,
heterocyclic molecules such as coumarins, 5 indoles
and benzofurans and other useful compounds.4,7
herein the free-energy of activation (”G#) for
restricted rotation around the C-NH bond of
zwitterionic salt 4b is described.
6
Recently we prepared an unusual charge-
separated Guanidium-meldrum acid zwitterionic

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AMINKHANI, Orient. J. Chem., Vol. 30(4), 1791-1797 (2014)
MATERIALAND METHODS
NH), 166.66 (2C, s, 2C=O) ppm. MS, m/z (%): 347
(M+, < 1), 246 (34), 173 (100), 160 (41), 115 (79), 91
(21), 71 (52), 43 (37). Anal. Calcd for C18H25N5O3
General
Compounds 1–3 were obtained from Fluka (347.41): C, 62.23; H, 7.25; N, 12.10. Found: C, 62.18;
and Merck and were used without further H, 7.17; N, 12.20
purification. The following instruments were used:
mp., Electrothermal-9100 apparatus, uncorrected; 5-{((bis (dimethylamino) methylene) ammonio) (p-
IR spectra, Shimadzu IR-460 spectrometer; 1H and tolyl) methyl}-2, 2-dimethyl-4, 6-dioxo-1, 3-dioxin-
13C NMR spectra, Bruker DRX-300 AVANC E 5-ide (4b)
instrument; in CDCl3 at 300.1 MHz and 75.4 MHz,
White powder, mp 182-184 °C (decomp),
respectively,  in ppm, J in Hz; EI-MS (70 eV): 0.275 g, (76%). IR (KBr) (max/cm-1): 1608 (C=O),
1
Finnigan-MAT-8430 mass spectrometer, in m/z. 1681 (C=N), 3236 (NH). H NMR (300.1 MHz,
Elemental analyses (C, H, N) were performed with CDCl3): 1.55 (6H, s, CMe2), 2.28 (3H, s, Me), 2.92
a Heraeus CHN-O-Rapid analyzer.
and 2.98 (12H, 2s, 2NMe2), 5.67 (1H, d, 3JHH = 8.5
Hz, HN-CH), 7.08 (2H, d, J = 7.8 Hz, 2 CH), , 7.38
General procedure for preparation of Guanidium- (2H, d, J = 7.8 Hz, 2CH), 8.97 (1H, d, 3JHH = 8.5 Hz,
meldrum acid zwitterionic salts (exemplified by NH) ppm. 13C NMR (75.4 MHz, CDCl3):  21.42
4b)
(Me), 26.34 (CMe2), 40.07, 40.73 (2NMe2), 57.22
To a magnetically stirred of 0.158 g of (HN-CH), 77.05 (HC-C-C), 102.26, (CMe2), 126.00
meldrum acid (1.1 mmol) and 0.120 g of 4- (2CH), 129.38 (2CH), 136.56 (C), 140.57 (C),
methylbenzaldehyde (1.0 mmol) in 10 cm3 of dry 161.70 (N-C-NH), 166.65 (2C, s, 2C=O) ppm. MS,
benzen (distilled from Na/benzophenone, 5.0 mL, m/z (%): 361 (M+, < 1), 246 (91), 188 (84), 173 (97),
0.2 M) was added 200 µL of a 0.5 mM solution of 160 (30), 144 (22), 115 (100), 105 (16), 71 (45), 57
pyrrolidinium acetate in benzene (prepared by (18), 43 (34). Anal. Calcd for C19H27N3O4 (361.44):
dropwise addition of AcOH to piperidine in benzene, C, 63.14; H, 7.53; N, 11.63 Found: C, 63.27; H, 7.59;
0.1 mmol, 10 mol%) and stirred about 20 hour.Then N, 11.58.
the reaction mixture was washed with saturated
NaHCO3 solution (2 × 10 mL).Then 0.115 g of N, N, 5-{((bis (dimethylamino) methylene) ammonio) (o-
N’, N’-Tetramethyl-guanidine (1.0 mmol) in 3 cm3 of tolyl) methyl}-2, 2-dimethyl-4, 6-dioxo-1, 3-dioxin-
benzen was added to organic layer over one minute 5-ide (4c)
at room temperature. After less four hours stirring at
White powder, mp 187-189 °C (decomp),
room temperature, the solvent was removed and 0.300 g, (83 %). IR (KBr) (max/cm”1): 1635 (C=O),
1
the crude product washed by acetone (2 × 3 mL), 1682 (C=N), 3229 (NH). H NMR (300.1 MHz,
and residue powder filtered.
CDCl3):  1.53 (6H, s, CMe2), 2.38 (3H, s, Me), 2.90
and 2.95 (12H, 2s, 2NMe2), 5.85 (1H, d, 3JHH = 8.6
3
5-{((bis (dimethylamino) methylene) ammonio) Hz, HN-CH), 7.20 (1H, t, JHH = 7.4 Hz, CH), 7.28
(phenyl) methyl}-2, 2-dimethyl-4, 6-dioxo-1, 3- (2H, d, 3JHH = 7.4 Hz, 2CH), 7.56 (2H, d, 3JHH = 7.4
dioxin-5-ide (4a)
Hz, 2CH), 8.44. (1H, d, 3JHH = 8.6 Hz, NH) ppm. 13
C
White powder, mp 168-170 °C (decomp), NMR (75.4 MHz, CDCl3):  20.13 (Me), 26.23
0.236 g, (68%). IR (KBr) (max/cm-1): 1612 (C=O), (CMe2), 39.97, 40.44 (2NMe2), 55.29 (HN-CH),
1
1681 (C=N), 3254 (NH). H NMR (300.1 MHz, 76.47 (HC-C-C) 101.96 (CMe2), 126.09 (CH),
CDCl3):  1.56 (6H, s, CMe2), 2.92 and 2.99 (12H, 126.45 (CH), 126.91 (CH), 130.62 (CH), 134.96 (C),
2s, 2NMe2), 5.67 (1H, d, 3JHH = 8.6 Hz, HN-CH), 7.20 140.77 (C), 161.45 (N-C-NH), 166.57 (2C, s, 2C=O)
(1H, t, 3JHH = 7.4 Hz, CH), 7.28 (2H, d, 3JHH = 7.4 Hz, ppm. MS, m/z (%): 361 (M+, < 1), 246 (73), 188 (87),
2CH), 7.56 (2H, d, 3JHH = 7.4 Hz, 2CH), 9.05 (1H, d, 173 (94), 160 (37), 144 (19), 115 (100), 105 (9), 71
3JHH = 8.6 Hz, NH) ppm. 13C NMR (75.4 MHz, CDCl3): (37), 57 (23), 43 (49). Anal. Calcd for C19H27N3O4
 26.33 (CMe2), 40.08, 40.79 (2NMe2), 57.37 (HN- (361.44): C, 63.14; H, 7.53; N, 11.63. Found: C, 63.24;
CH), 77.05 (HC-C-C) 102.32 (CMe2), 126.1 (2CH), H, 7.59; N, 11.56.
127.4 (CH), 128.9 (2CH), 143.8 (C), 161.74 (N-C-

AMINKHANI, Orient. J. Chem., Vol. 30(4), 1791-1797 (2014)
1793
5-{((bis (dimethylamino) methylene) ammonio)
(m-tolyl) methyl}-2, 2-dimethyl-4, 6-dioxo-1, 3-
dioxin-5-ide (4d)
NH) ppm. 13C NMR (75.4 MHz, CDCl3): ´ 26.37
(CMe2), 40.12, 40.72 (2NMe2), 56.76 (HN-CH),
77.09 (HC-C-C), 102.25, (CMe2), 125.38 (CH),
125.86 (CH), 127.34 (CH), 129.56 (CH), 134.23
(C), 146.07 (C), 161.95 (N-C-NH), 165.56 (2C, s,
2C=O) ppm. MS, m/z (%): 383 (M+ + 2, < 1), 382 (M+
+ 1, < 1), 381 (M+, 2), 245 (84), 208 (43), 196 (27),
180 (27), 173 (100), 164 (33), 136 (80), 115 (53),
71 (39), 57 (24), 43 (39). Anal. Calcd for
C18H24ClN3O4 (381.84): C, 56.62; H, 6.34; N, 11.00.
Found: C, 56.68; H, 6.465; N, 11.10.
White powder, mp 180-183 °C (decomp),
0.286 g, (79 %). IR (KBr) (max/cm”1): 1612 (C=O),
1
1682 (C=N), 3262 (NH). H NMR (300.1 MHz,
CDCl3):  1.56 (6H, s, CMe2), 2.30 (3H, s, Me), 2.92
and 2.99 (12H, 2s, 2NMe2), 5.67 (1H, d, 3JHH = 8.6
Hz, HN-CH), 6.98-7.30 (4H, m,Ar), 9.00 (1H, d, 3JHH
= 8.6 Hz, NH) ppm. 13C NMR (75.4 MHz, CDCl3): 
21.93 (Me), 26.33 (CMe2), 40.08, 40.79 (2NMe2),
57.37 (HN-CH), 77.05 (HC-C-C) 102.32 (CMe2),
123.13 (CH), 126.70 (CH), 127.85 (CH), 128.60
(CH), 138.20 (C), 143.41 (C), 161.74 (N-C-NH),
166.66 (2C, s, 2C=O) ppm. MS, m/z (%):361 (M+, <
1), 246 (68), 188 (73), 173 (100), 160 (29), 115
(96), 105 (22), 71 (40), 57 (16), 43 (31). Anal. Calcd
for C19H27N3O4 (361.44): C, 63.14; H, 7.53; N, 11.63.
Found: C, 63.09; H, 7.47; N, 11.68.
5-{((bis (dimethylamino) methylene) ammonio) (4-
fluorophenyl) methyl}-2, 2-dimethyl-4, 6-dioxo-1,
3-dioxin-5-ide (4g)
White powder, mp 173-175 °C (decomp),
0.267 g, (73 %). IR (KBr) (max/cm-1): 1597 (C=O),
1
1682 (C=N), 3171 (NH). H NMR (300.1 MHz,
CDCl3):  1.56 (6H, s, CMe2), 2.93 and 3.00 (12H,
3
2s, 2NMe2), 5.68 (1H, d, JHH = 8.6 Hz, HN-CH),
5-{((bis (dimethylamino) methylene) ammonio) (4-
chlorophenyl) methyl}-2, 2-dimethyl-4, 6-dioxo-1,
3-dioxin-5-ide (4e)
6.96 (2H, t, J = 8.7 Hz, 2CH), 7.49 (2H, dd, J = 8.7,
5.4 Hz, 2CH), 8.96 (1H, d, 3JHH = 8.6 Hz, NH) ppm.
13C NMR (75.4 MHz, CDCl3):  26.32 (CMe2), 40.12,
40.80 (2NMe2), 56.88 (HN-CH), 77.03 (HC-C-C),
White powder, mp 188-190 °C (decomp),
0.267 g, (70 %). IR (KBr) (max/cm-1): 1612 (C=O),
3
102.37, (CMe2), 115.44 (d, JCF = 21 Hz, 2CH,),
1
2
4
1682 (C=N), 3186 (NH). H NMR (300.1 MHz,
127.69 (d, JCF = 7.5 Hz, 2CH), 139.38 (d, JCF =
CDCl3):  1.52 (6H, s, CMe2), 2.87 and 2.93 (12H,
2s, 2NMe2), 5.61 (1H, d, JHH = 8.7 Hz, HN-CH),
3.1Hz, C), 161.79 (N-C-NH), 162.00 (d, 1JCF = 245
Hz, CF), 166.56 (2C, s, 2C=O) ppm. MS, m/z (%):
365 (M+, < 1), 245 (71), 192 (34), 173 (94), 160
(17), 148 (57), 115 (100), 71 (41), 57 (33), 43 (57).
Anal. Calcd for C18H24FN3O4 (365.40): C, 59.17; H,
6.62; N, 11.50 Found: C, 59.04; H, 6.54; N, 11.58.
3
7.19. (2H, d, J = 8.4 Hz, 2CH), 7.34 (2H, d, J = 8.4
Hz, 2CH), 8.83 (1H, d, 3JHH = 8.7 Hz, NH) ppm. 13
C
NMR (75.4 MHz, CDCl3):  26.33 (CMe2), 40.02,
40.74 (2NMe2), 56.82 (HN-CH), 77.11 (HC-C-C),
102.29 (CMe2), 127.53 (2CH), 128.71 (2CH),
132.57 (C), 142.08 (C), 161.83 (N-C-NH), 166.46
(2C, s, 2C=O) ppm. MS, m/z (%): 383 (M+ + 2, 1),
382 (M+ + 1, 1), 381 (M+, 4), 368 (20), 245 (91), 208
(58), 196 (39), 180 (46), 173 (100), 164 (48), 136
(74), 115 (30), 101 (30), 71 (55), 57 (31), 43 (37).
Anal. Calcd for C18H24ClN3O4 (381.84): C, 56.62; H,
6.34; N, 11.00. Found: C, 56.52; H, 6.44; N, 11.12.
5-{((bis (dimethylamino) methylene) ammonio) (2-
fluorophenyl) methyl}-2, 2-dimethyl-4, 6-dioxo-1,
3-dioxin-5-ide (4h)
White powder, mp 176-178 °C (decomp),
0.296 g, (81 %). IR (KBr) (max/cm-1): 1620 (C=O),
1
1678 (C=N), 3198 (NH). H NMR (300.1 MHz,
CDCl3):  1.68 (6H, s, CMe2), 2.89 and 3.06 (12H,
3
2s, 2NMe2), 5.99 (1H, d, JHH = 9.4 Hz, HN-CH),
3
5-{((bis (dimethylamino) methylene) ammonio) (2-
chlorophenyl) methyl}-2, 2-dimethyl-4, 6-dioxo-1,
3-dioxin-5-ide (4f)
6.92-7.64 (4H, m, Ar), 8.28. (1H, d, JHH = 9.4 Hz,
NH) ppm. 13C NMR (75.4 MHz, CDCl3):  26.49
(CMe2), 39.82, 40.45 (2NMe2), 51.38 (HN-CH),
3
White powder, mp 181-183 °C (decomp),
0.275 g, (72 %). IR (KBr) (max/cm”1): 1608 (C=O),
72.87 (HC-C-C) 102.41 (CMe2), 115.37 (CH, d,
JFC = 21.3 Hz,), 125.2 (d, 2JFC = 9.4 Hz, CH), 129.6
(d, 3JFC = 22.4 Hz, CH), 129.8 (d, 2JFC = 9.9 Hz, C),
129.8 (CH, d, 4JFC = 3.0 Hz,), 160.83 (d, 1JFC = 243.2
Hz, CF) 161.01 (N-C-NH), 167.02 (2C, s, 2C=O)
ppm. MS, m/z (%): 365 (M+, < 1), 245 (71), 173 (94),
1
1679 (C=N), 3236 (NH). H NMR (300.1 MHz,
CDCl3):  1.57 (6H, s, CMe2), 2.98 and 3.03 (12H,
3
2s, 2NMe2), 5.68 (1H, d, JHH = 8.7 Hz, HN-CH),
3
7.24-7.49 (4H, m, Ar), 9.00. (1H, d, JHH = 8.7 Hz,

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AMINKHANI, Orient. J. Chem., Vol. 30(4), 1791-1797 (2014)
160 (17), 148 (57), 115 (100), 71 (41), 57 (53), 43 CDCl3):  1.77 (6H, s, CMe2), 2.96 and 2.99 (12H,
(57). Anal. Calcd for C18H24FN3O4 (365.40): C, 59.17; 2s, 2NMe2), 3.16 (Ar-NMe2), 5.66 (1H, d, 3JHH = 7.8
H, 6.62; N, 11.50. Found: C, 59.06; H, 6.54; N, 11.57. Hz, HN-CH), 6.68 (2H, d,J = 8.7 Hz, 2CH), 8.27 (2H,
d, J = 8.7 Hz, 2CH), 8.93 (1H, d, 3JHH = 7.8 Hz, NH)
5-{((bis (dimethylamino) methylene) ammonio) (4- ppm. 13C NMR (75.4 MHz, CDCl3):  26.34 (CMe2),
nitrophenyl) methyl}-2, 2-dimethyl-4, 6-dioxo-1, 3- 39.81, 40.48 (2NMe2), 41.05 (Ar-NMe2) 56.90 (HN-
dioxin-5-ide (4i)
CH), 77.01 (HC-C-C), 102.19, (CMe2), 112.92
Yellow powder, mp 191-193 °C (decomp), (2CH), 127.06 (2CH), 131.69 (C), 149.88 (C), 161.52
0.302 g, (77 %). IR (KBr) (max/cm-1): 1612 (C=O), (N-C-NH), 166.78 (2C, s, 2C=O) ppm. MS, m/z (%):
1
1682 (C=N), 3194 (NH). H NMR (300.1 MHz, 390 (M+, < 1), 246 (89), 217 (21), 173 (94), 160 (31),
CDCl3):  1.55 (6H, s, CMe2), 2.92 and 3.01 (12H, 142 (16), 115 (100), 89 (27), 71 (42), 57 (24), 43
3
2s, 2NMe2), 5.73 (1H, d, JHH = 8.9 Hz, HN-CH), (42). Anal. Calcd for C20H30N4O4 (390.23): C, 61.52;
7.71. (2H, d,J = 8.7 Hz, 2CH), 8.13 (2H, d,J = 8.7 Hz, H, 7.74; N, 14.35. Found: C, 61.60; H, 7.84; N, 14.39.
2CH), 8.92 (1H, d, 3JHH = 8.9 Hz, NH) ppm. 13C NMR
(75.4 MHz, CDCl3):  26.34 (CMe2), 40.28, 40.89 (2 5-{((bis (dimethylamino) methylene) ammonio) (4-
NMe2), 57.11 (HN-CH), 77.07 (HC-C-C), 102.61, bromophenyl) methyl}-2, 2-dimethyl-4, 6-dioxo-1,
(CMe2), 124.03(2CH), 126.78 (2CH), 147.01 (C), 3-dioxin-5-ide (4l)
150.69 (C), 162.12 (N-C-NH), 166.41 (2C, s, 2C=O)
White powder, mp 204-206 °C (decomp),
ppm. MS, m/z (%): 392 (M+, < 1), 245 (100), 219 0.324 g, (76 %). IR (KBr) (max/cm-1): 1613 (C=O),
1
(24), 196 (92), 152 (52), 122 (5), 115 (4), 71 (22), 57 1682 (C=N), 3193 (NH). H NMR (300.1 MHz,
(20), 43(18). Anal. Calcd for C18H24N4O6 (392.41): C, CDCl3): ´ 1.574 (6H, s, CMe2), 2.89 and 2.96 (12H,
55.09; H, 6.16; N, 14.28. Found: C, 55.22; H, 6.19; N, 2s, 2NMe2), 5.62 (1H, d, 3JHH = 8.7 Hz, HN-CH), 7.38
14.16.
(4H, s, Ar) 8.87 (1H, d, 3JHH = 8.7 Hz, NH) ppm. 13
C
NMR (75.4 MHz, CDCl3):  26.35 (CMe2), 40.05,
5-{((bis (dimethylamino) methylene) ammonio) (4- 40.81 (2NMe2), 56.91 (HN-CH), 77.07 (HC-C-C),
methoxyphenyl) methyl}-2, 2-dimethyl-4, 6-dioxo- 102.36, (CMe2), 120.73 (C), 127.91 (2CH), 131.69
1, 3-dioxin-5-ide (4j)
(2CH), 142.57 (C), 161.87 (N-C-NH), 166.50 (2C,
White powder, mp 169-171 °C (decomp), s, 2C=O) ppm. MS, m/z (%): 427 (M+, < 1), 425 (M+,
0.321 g, (85 %). IR (KBr) (max/cm-1): 1612 (C=O), < 1), 325 (14), 246 (58), 253 (21), 173 (89), 209
1
1682 (C=N), 3194 (NH). H NMR (300.1 MHz, (19), 160 (31), 115 (100), 71 (29), 57 (24), 43 (38).
CDCl3):  1.55 (6H, s, CMe2), 2.90 and 2.96 (12H, Anal. Calcd for C18H24BrN3O4 (426.30): C, 61.52; H,
2s, 2NMe2), 3.74 (3H, s, OMe), 5.63 (1H, d, 3JHH
=
7.74; N, 14.35. Found: C, 61.60; H, 7.81; N, 14.39.
RESULTSAND DISCUSSION
8.4 Hz, HN-CH), 6.78 (2H, d,J = 8.7 Hz, 2CH), , 7.39
(2H, d, J = 8.7 Hz, 2CH), 8.94 (1H, d, 3JHH = 8.4 Hz,
NH) ppm. 13C NMR (75.4 MHz, CDCl3):  26.34
(CMe2), 40.05, 40.71 (2NMe2), 55.62 (OMe), 56.93
The three component condensation
(HN-CH), 77.08 (HC-C-C), 102.24, (CMe2), 114.05 reactions of Meldrum acid 1, benzaldehyde
(2CH), 127.29 (2CH), 135.91 (C), 158.71 (C), 161.62 derivatives 2, and N, N, N’, N’-Tetramethyl-guanidine
(N-C-NH), 166.62 (2C, s, 2C=O) ppm. MS, m/z (%): 3 proceeded with piperidinium acetate at room
377 (M+, 1), 246 (82), 204 (19), 189 (11), 173 (100), temperature in benzene and were complete within
1
160 (62), 121 (19), 115 (57), 71 (34), 57 (43), 43 about a day. Analysis of the IR, H and 13C NMR
(31). Anal. Calcd for C19H27N3O5 (377.43): C, 60.46; spectroscopy, and mass spectrometry spectra as
H, 7.21; N, 11.13. Found: C, 60.54; H, 7.27; N, 11.06. well as elemental analysis confirm the formation
and isolation of the desired zwitterion salts as
5-{((bis (dimethylamino) methylene) ammonio) (4- shown in scheme 1. The IR spectrum of 4b exhibits
(dimethylamino) phenyl) methyl}-2, 2-dimethyl-4, a NH stretching band at 3236 cm-1, signals for
6-dioxo-1, 3-dioxin-5-ide (4k)
carbonyl groups at 1601 cm-1 and for C=N at 1682
White powder, mp 123-125 °C (decomp), cm-1. The H NMR spectrum of 4b exhibited four
0.289 g, (74 %). IR (KBr) (max/cm-1): 1604 (C=O), single sharp lines readily recognized as CMe2 ( =
1
1
1682 (C=N), 3333 (NH). H NMR (300.1 MHz, 1.55 ppm), Ar-Me ( = 2.28 ppm), two NMe2 groups

AMINKHANI, Orient. J. Chem., Vol. 30(4), 1791-1797 (2014)
1795
( = 2.92, 2.98 ppm), along with two characteristic
doublets ( = 5.67 and 8.97 ppm, 3JHH = 8.5) for the
H-C-NH moiety. All aromatic protons resonate at 
= 7.05-7.38 ppm.
O
O
N
O
O
H
piperidinium acetate
10 mol %
O
2
NH
O
O
Ar
+
+
Ar
H
N
N
O
O
N
N
Benzen
4
3
1
2,4
a
b
c
d
e
f
g
h
i
Ar
Ph
p-T olyl
o-T olyl
Yield(%) of 4
68
76
83
79
70
72
73
81
77
85
74
76
m-Tolyl
4-ClC6H4
2-ClC6H4
4-FC6H4
2-FC6H4
4-NO2C6H4
4-OMeC6H4
4-N,N-diMeC6H4
4-BrC6H4
j
k
l
Scheme 1: Synthesis of Guanidium-Meldrum acid zwitterionic salts
The H-decoupled 13C NMR spectrum of
4b showed six distinct signals below 100 ppm,
which were readily recognized as arising from Ar-
Me ( = 21.42 ppm), CMe2 groups ( = 26.34 ppm),
two NMe2 groups ( = 40.06, 40.73 ppm), methine
( = 57.22, 77.05 ppm) carbon atoms.The meldrum
acid residue showed only one signal for the
carbonyl ( = 166.65) group, which is consistent
with the presence of a local Cs symmetry, which
exhibited characteristic signals with appropriate
chemical shifts. The 1H and 13C NMR spectra of the
other compounds are similar to those of 4b except
for the aryl groups, which exhibit characteristic
signals with appropriate chemical shifts. The mass
and elemental analyses data were in agreement
with the proposed structures. The formation of
zwitterionic salts 4 can be rationalized by initial
formation of a conjugated electron-deficient
heterodyne 5 through Knoevenagel condensation8
1
of the 1 and benzaldehydes 2 using piperidinium
9, 11
acetate followed by a Michael-type
addition
reaction with N, N, N’, N’-Tetramethyl-guanidine 3
to afford compound 4 as shown in scheme 2. We
didn’t detect any cyclization of synthetic compounds
12
at room temperature,
microwave irradiation.
refluxing for 5h and
N
O
O
N
HN
O
O
O
O
H
N
O
O
H
O
2
knoevenagel
-H2O
O
O
O
O
O
O
3
+
NMe2
Ar
Ar
H
O
Ar
N
H
Ar
O
NMe2
N
N
6
5
1
4
Scheme 2: Proposed mechanism for the formation of Guanidium-Meldrum acid zwitterionic salts

1796
AMINKHANI, Orient. J. Chem., Vol. 30(4), 1791-1797 (2014)
The H NMR spectrum of 4b in CDCl3 at the N-C bond rotation in 4b at 308 K as shown in
1
ambient temperature displayed two single Table. Application of the absolute rate theory with a
resonances due to the NMe2 ( = 2.96, 3.02) protons. transmission coefficient of 4b gave free-energy
At about + 30 °C, the resonances arising from the activation (G#) of 66 2 k Jmol-1, where all known
14
NMe2 protons were appreciably broadened when sources of errors were estimated and included.
compared to the corresponding signals at room Only two 1:1 singlets are observed for the four
temperature, whereas other group’s resonances diastereotopic methyl groups of the guanidino
remained unchanged. The NMe2 protons moiety in the 1H and 13C NMR spectra of 4b at room
coalescences near + 35 °C and appeared as a fairly temperature. Two rotational processes, i) C–NH
symmetrical line at + 40 °C.The variable temperature bond rotation (A, B) and ii) C–NMe2 bond rotation
spectra allowed calculating the free-energy barrier (C), can be envisaged in the guanidino moiety of 4.
for the C-NH bond two NMe2 groups rotation in 4b When both of these processes are fast on the NMR
(Scheme 3). Using the expression k = /2, first timescale, the four Me groups become equivalent
order rate constant (k = 39.96 s-1) was calculated for and exhibit a single resonance, as for the spectra
O
O
N
O
O
N
O
O
N
O
O
H
O
O
H
O
O
H
Ar
Ar
Ar
N
N
N
N
N
N
A
B
C
Scheme 3: Dynamic effect of synthesized zwitterionic salts
Table 1: Selected 1H chemical shifts (300 MHz)
and activation parameters of 4b in CDCl3
Temp(°C)
Resonance (NMe2)
(Hz)
K(S-1)
Tc(K)
G#(KJmol-1)
35
30
2.99
2.96 3.02
-
18
-
308
-
-
39.96
66
2
observed above 308 K. two observed signals for along with three component condensation in
these groups’ shows one of the processes should benzene in presence of piperidinium acetate at
be fast on the NMR timescale. We conceder the room temperature within one day. A dynamic NMR
1
contribution of the valence-bond structures A and B effect is observed in the H NMR spectra of these
to the resonance hybrid of 4 is in fact more important compounds as a result of restricted rotation around
than that of C for the simple reason that they C-NH bond for two NMe2 groups.
correspond to a more highly substituted carbon–
nitrogen double bond.14 Therefore the faster process
can be the C–NH rotation (process i). In summary,
we have reported the synthesis of guanidinium
ACKNOWLEDGMENTS
Author gratefully acknowledges financial
zwitterionic salts by an efficient and simple approach support from the Research Council of Khoy Branch
Islamic Azad University.

AMINKHANI, Orient. J. Chem., Vol. 30(4), 1791-1797 (2014)
1797
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