Synthesis of new thiophene, furan and pyridine substituted 1,2,4,5-oxadiazaboroles

Article abstract of DOI:10.1016/j.poly.2007.11.043

Twenty-two new 3,4,5-trisubstituted 1,2,4,5-oxadiazaboroles were prepared by the cyclocondensation reaction of N-substituted thiophene, furan and pyridine carboxamidoximes with phenylboronic acid in refluxing toluene in good yields. The structures of the

Full text of DOI:10.1016/j.poly.2007.11.043

Available online at www.sciencedirect.com
Polyhedron 27 (2008) 999–1007
www.elsevier.com/locate/poly
Synthesis of new thiophene, furan and pyridine substituted
1,2,4,5-oxadiazaboroles
a,
a
b
b
b
*
Yaßsar Durust , Muharrem Akcan , Olli Martiskainen , Elina Siirola , Kalevi Pihlaja
¨ ¨
a
_
Department of Chemistry, Abant Izzet Baysal University, TR 14280, Bolu, Turkey
b Department of Chemistry, University of Turku, FIN 20014, Turku, Finland
Received 3 October 2007; accepted 28 November 2007
Available online 29 January 2008
Abstract
Twenty-two new 3,4,5-trisubstituted 1,2,4,5-oxadiazaboroles were prepared by the cyclocondensation reaction of N-substituted thi-
ophene, furan and pyridine carboxamidoximes with phenylboronic acid in refluxing toluene in good yields. The structures of the new
1
oxadiazaboroles were elucidated by means of spectral measurements (IR, H, 13C, 11B NMR, MS, X-ray) and physical data (melting
points, elemental compositions by HRMS).
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Oxadiazaboroles; Cyclocondensation; Amidoxime; Thiophene; Furan; Pyridine
1. Introduction
2. Experimental
Amidoximes are versatile precursors of many heterocy-
clic compounds of pharmaceutical importance [1,2]. On
the other hand, aryl boronic acids and their esters are
highly popular as synthetic intermediates in organic syn-
thesis for their ease of conversion to other functional
groups (such as phenols and aryl halides) with well-known
reactivity [3–6]. To our best knowledge, a literature survey
of oxadiazaboroles from amidoxime and phenyl boronic
acid reveals that only a limited number of reports were
given in the 1960s and 1970s, and no spectral data were
supplied for those heterocycles [7–10]. As an ongoing
research on assembling amidoxime-based heterocyclic
compounds, we report here the preparation and mass spec-
tra of new thiophene, furan and pyridine substituted
1,2,4,5-oxadiazaboroles.
2.1. Materials and general methods
All reactions were performed under dry argon or nitro-
gen atmosphere. Aldehydes, N-chlorosuccinimide and pri-
mary amines were purchased from Merck and Fluka.
1
Phenylboronic acid was purchased from Aldrich. H and
13C NMR spectra were recorded on Bruker and Varian
spectrometers (300 and 400 MHz for proton, 75 and
100 MHz for carbon). 11B NMR spectra of the samples
(1–19 mg) were recorded on a Bruker Avance 500 spec-
trometer (Bruker Bio Spin Scandinavia AB, Ta¨by, Sweden)
equipped with a BBO-5 mm-Zgrad probe with CDCl3 as
the solvent and referenced to a standard 15% BF3–Et2O
sample (0.00 ppm frequency given by Bruker software).
The spectra were recorded at 160.46 MHz by non-decou-
pled single pulse excitation with a 30° pulse angle and
1000–10000 scans. IR spectra were recorded on a JASCO
430 FT/IR instrument (as KBr pellets). Mass spectra were
measured on an Agilent GC 6890N gas chromatograph
with mass detector MS 5975. High resolution mass spectra
of the compounds were measured on a VG ZabSpec mass
spectrometer (Micromass, Manchester, UK) equipped with
*
Corresponding author. Tel.: +90 374 2541243; fax: +90 374 2534642.
E-mail address: yasardurust@ibu.edu.tr (Y. Durust).
¨ ¨
0277-5387/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.11.043

1000
Y. Du¨ru¨st et al. / Polyhedron 27 (2008) 999–1007
the Opus V3.3X program package. Melting points were
determined on a Meltemp apparatus and were uncorrected.
Flash column chromatography was performed on Silica
Gel (Merck, 230–400 Mesh ASTM). TLC was done using
pre-coated plates with a fluorescent indicator (Merck
5735). The stain solutions of permanganate, p-anisaldehyde
and iodine were used for visualization of the TLC spots.
(C@N). 1H NMR (300 MHz, CDCl3 + DMSO-d6): d
10.32 (s, 1H, NOH), 7.23 (s, 1H, NH), 6.86 (m, 2H), 6.76
(m, 2H), 6.67 (m, 1H), 6.52 (m, 1H), 3.76 (s, 3H, OCH3).
13C NMR (75 MHz, CDCl3 + DMSO-d6): d 156.37,
146.66, 133.12, 132.87, 130.42, 127.52, 126.21, 124.98,
114.13, 55.49. MS (m/z,%): M–H2O, 264 (100), 249 (88),
221 (21).
Thiophene-2-carboxaldehyde
oxime,
furan-2-
carbaldehydeoxime, thiophene-2-hydroximoyl chloride,
5-chloro-thiophene-2-hydroximoyl chloride, 5-chloro-
furan-2-hydroximoyl chloride, N-(p-methoxyphenyl)thio-
phene-2-carboxamidoxime and N-p-tolylthiophene-2-car-
boxamidoxime were prepared by utilizing literature
procedures described previously [12–17].
2.2.4. N-(4-Chlorophenyl)-5-chloro-thiophene-2-
carboxamidoxime (3f)
Light yellow needles (hexane–ethyl acetate). Yield: 73%.
M.p. 97–99 °C. Rf: 0.50 (hexane:ethyl acetate; 3:2). IR
(KBr, m: cmÀ1): 3382 (N–H), 3215 (broad, NOH), 1626
(C@N). 1H NMR (300 MHz, CDCl3 + DMSO-d6): d 10.64
(s, 1H, NOH), 7.66 (s, 1H, NH), 7.14 (d, J = 9.2 Hz, 2H),
7.03 (d, J = 9.2 Hz, 2H), 6.79 (d, J = 6.7 Hz, 1H), 6.73 (d,
J = 4.9 Hz, 1H), 6.66 (d, J = 4.1 Hz, 1H), 6.59 (d,
J = 9.1 Hz, 1H). 13C NMR (75 MHz, CDCl3 + DMSO-
d6): d 145.80, 145.15, 139.26, 132.74, 130.76, 128.99,
128.78, 127.67, 127.49, 126.41, 122.61, 116.20. MS (m/
z,%): M–H2O, 268 (100), 233 (40), 198 (5).
2.2. Synthesis of N-substituted amidoximes
2.2.1. N-Phenyl-5-chloro-thiophene-2-carboxamidoxime
(3a)
To a solution of 5-chloro-thiophene-2-hydroximoyl
chloride (2a) (0.98 g, 6.06 mmol) in chloroform (20 mL)
was added dropwise aniline (1.13 g, 12.1 mmol) in chloro-
form with constant stirring at room temperature. The reac-
tion mixture was stirred for 2 d. The precipitate was filtered
and the solution was evaporated under reduced pressure.
The residual solid was subjected to flash column chroma-
tography (eluant: hexane:ethyl acetate; 1:3) to give N-phe-
nyl-5-chloro-thiophene-2-carboxamidoxime (3a), 0.78 g,
yield: 65%. M.p. 131–133 °C. Rf: 0.42 (hexane:ethyl ace-
tate; 3:1). IR (KBr, m: cmÀ1): 3368 (N–H), 3204–3099
(broad, NOH), 1630 (C@N). 1H NMR (400 MHz,
CDCl3 + DMSO-d6): d 9.98 (broad s, 1H), 7.20 (broad s,
1H), 6.95 (t, 1H), 6.82 (d, J = 7.4 Hz, 2H), 6.65 (d,
J = 3.9 Hz, 1H), 6.61 (d, J = 3.9 Hz, 1H). 13C NMR
(100 MHz, CDCl3 + DMSO-d6): d 145.13, 140.00, 132.62,
130.00, 128.40, 127.06, 125.93, 122.46, 121.20, 119.92.
MS (m/z,%): 252 (M+,32), 235 (76), 220 (16), 200 (12),
143 (23), 93 (100), 77 (31), 65 (22), 51 (14).
2.2.5. N-(4-Bromophenyl)-5-chloro-thiophene-2-
carboxamidoxime (3g)
Yield: 84%. M.p. 143–145 °C. Rf: 0.61 (hexane:ethyl ace-
tate; 3:2). IR (KBr, m: cmÀ1): 3387 (N–H), 3235 (broad,
NOH), 1630 (C@N). 1H NMR (300 MHz, CDCl3 +
DMSO-d6): d 10.60 (s, 1H, NOH), 7.54 (d, J = 7.0 Hz,
1H, NH), 7.27 (m, 2H), 6.72 (m, 3H). 13C NMR
(75 MHz, CDCl3 + DMSO-d6): d 145.46, 139.57, 132.35,
131.90, 131.20, 127.74, 126.50, 123.20, 115.73.MS (m/
z,%): M–H2O, 314 (100), 279 (47), 198 (12).
2.2.6. N-(4-Iodophenyl)-5-chloro-thiophene-2-
carboxamidoxime (3h)
Yield: 50%. M.p. 141–144 °C. Rf: 0.50 (hexane:ethyl ace-
tate; 3:1). IR (KBr, m: cmÀ1): 3394 (N–H), 3217 (broad,
NOH), 1636 (C@N). 1H NMR (300 MHz, CDCl3 +
DMSO-d6): d 10.63 (s, 1H, NOH), 7.56 (s, 1H, NH), 7.44
(m, 2H), 6.78–6.61 (m, 4H). 13C NMR (75 MHz,
CDCl3 + DMSO-d6): d 144.84, 140.48, 137.58, 132.74,
130.76, 127.46, 126.43, 123.06, 122.02, 85.40. MS (m/
z,%): M–H2O, 362 (100), 346 (14), 219 (35), 144 (16).
2.2.2. N-(4-Methylphenyl)-5-chloro-thiophene-2-
carboxamidoxime (3c)
Colourless needles (hexane–ethyl acetate). Yield: 50%.
M.p. 132–134 °C. Rf: 0.54 (hexane:ethyl acetate; 3:1). IR
(KBr, m: cmÀ1): 3363 (N–H), 3213–3171 (broad, NOH),
1
1627 (C@N). H NMR (300 MHz, CDCl3 + DMSO-d6):
2.2.7. N-(1-Naphthyl)-5-chloro-thiophene-2-
carboxamidoxime (3i)
d 10.41 (s, 1H, NOH), 7.29 (s, 1H, NH), 6.98 (d,
J = 7.9 Hz, 2H), 6.78 (d, J = 7.6 Hz, 2H), 6.70 (m, 1H),
6.60 (m, 1H), 2.23 (s, 3H). 13C NMR (75 MHz,
CDCl3 + DMSO-d6): d 146.05, 137.66, 132.98, 130.34,
129.42, 127.46, 126.25, 122.35, 20.83. MS (m/z,%): M–
H2O, 248 (100), 213 (47), 77 (11).
Yield: 65%. M.p. 168–170 °C. Rf: 0.44 (hexane:ethyl ace-
tate; 3:1). IR (KBr, m: cmÀ1): 3381 (N–H), 3224–3103
(broad, NOH), 1632 (C@N). 1H NMR (300 MHz,
CDCl3 + DMSO-d6): d 10.61 (s, 1H, NOH), 8.20 (m, 1H),
7.85 (m, 1H), 7.62–7.26 (m, 5H), 6.95 (d, J = 7.3 Hz, 1H),
6.60 (d, J = 1.1 Hz, 1H), 6.45 (d, J = 1.1 Hz, 1H). 13C
NMR (75 MHz, CDCl3 + DMSO-d6): d 146.98, 136.14,
134.22, 133.05, 130.18, 128.94, 128.34, 126.91, 126.39,
126.33, 126.17, 125.47, 124.71, 122.25, 121.06. MS (m/
z,%): M–H2O, 284 (100), 249 (18), 140 (6).
2.2.3. N-(4-Methoxyphenyl)-5-chloro-thiophene-2-
carboxamidoxime (3e)
White plates (hexane–ethyl acetate). Yield: 65%. M.p.
140–142 °C. Rf: 0.45 (hexane:ethyl acetate; 3:1). IR (KBr,
m: cmÀ1): 3344 (N–H), 3234–3111 (broad, NOH), 1631

Y. Du¨ru¨st et al. / Polyhedron 27 (2008) 999–1007
1001
2.2.8. N-Phenyl-5-chloro-furan-2-carboxamidoxime (3j)
Yield: 20%. M.p. 147–149 °C. Rf: 0.29 (hexane:ethyl ace-
tate; 3:1). IR (KBr, m: cmÀ1): 3384 (N–H), 3119–2945
1H). 13C NMR (75 MHz, CDCl3 + DMSO-d6): d 145.10,
141.59, 139.73, 137.06, 131.55, 121.44, 120.21, 114.45,
113.48, 108.00. MS (m/z,%): M–H2O, 298 (100), 270 (35),
233 (27), 189 (22).
1
(broad NOH), 1627 (C@N). H NMR (300 MHz, CDCl3
+ DMSO-d6): d 10.52 (s, 1H, NOH), 7.47 (s, 1H, NH),
7.18 (m, 2H), 6.97 (m, 1H), 6.75 (d, J = 8.2, 6.48 Hz,
1H), 6.21 (m, 1H). 13C NMR (75 MHz, CDCl3 +
DMSO-d6): d 145.24, 142.39, 140.24, 136.95, 128.85,
122.58, 120.28, 113.44, 107.91. MS (m/z,%): M–H2O, 218
(100), 190 (53), 155 (68).
2.2.13. N-(4-Iodophenyl)-5-chloro-furan-2-
carboxamidoxime (3o)
Yield: 26%. M.p. 165–167 °C. Rf: 0.58 (hexane:ethyl ace-
tate; 3:1). IR (KBr, m: cmÀ1): 3385 (N–H), 3082–2962
(broad, NOH), 1627 (C@N). 1H NMR (400 MHz,
CDCl3 + DMSO-d6): d 9.50 (broad s, 1H), 7.48 (d,
J = 8.5 Hz, 2H), 7.36 (broad s, 1H), 6.50 (d, J = 8.5 Hz,
2H), 6.46 (d, J = 3.3 Hz, 1H), 6.13 (d, J = 3.3 Hz, 1H).
13C NMR (100 MHz, CDCl3 + DMSO-d6): d 144.58,
141.56, 140.01, 137.39, 137.17, 121.79, 120.52, 113.61,
107.88, 84.96. MS (m/z,%): M–H2O (100), 316 (22), 281
(12), 217 (9), 189 (32), 172 (12), 154 (14), 127 (12).
2.2.9. N-(4-Methylphenyl)-5-chloro-furan-2-
carboxamidoxime (3k)
Yield: 40%. M.p. 157–159 °C. Rf: 0.23 (hexane:ethyl ace-
tate; 3:1). IR (KBr, m: cmÀ1): 3384 (N–H), 3089–2970
(broad, NOH), 1624 (C@N). 1H NMR (300 MHz,
CDCl3 + DMSO-d6): d 10.31 (s, 1H, NOH), 7.18 (s, 1H,
NH), 6.97 (d, J = 7.9 Hz, 2H), 6.66 (d, J = 8.4 Hz, 2H),
6.40 (d, J = 1.4 Hz, 1H), 6.16 (d, J = 1.6 Hz, 1H), 2.26 (s,
3H). 13C NMR (75 MHz, CDCl3 + DMSO-d6): d 145.23,
142.81, 137.59, 136.82, 132.29, 129.39, 120.89, 113.47,
107.82, 20.75. MS (m/z,%): M–H2O, 232 (100), 204 (51),
169 (56).
2.2.14. N-(1-Naphthyl)-5-chloro-furan-2-carboxamidoxime
(3p)
Yield: 30%. M.p. 128–129 °C. Rf: 0.49 (hexane:ethyl
acetate; 3:2). IR (KBr, m: cmÀ1): 3365 (N–H), 3143
(broad, NOH), 1636 (C@N). 1H NMR (300 MHz,
CDCl3 + DMSO-d6): d 10.56 (s, 1H, NOH), 8.16 (d,
J = 6.7 Hz, 1H), 7.85 (d, J = 7.6 Hz, 1H), 7.60 (d,
J = 8.2 Hz, 1H), 7.55–7.50 (m, 1H), 7.42 (s, 1H, NH),
7.28 (t, 1H), 6.87 (d, J = 7.3 Hz, 1H), 6.21 (d,
J = 3.5 Hz, 1H), 6.05 (d, J = 3.5 Hz, 1H). 13C NMR
(75 MHz, CDCl3 + DMSO-d6):d 145.10, 141.59, 139.73,
137.06, 131.55, 121.44, 120.21, 114.45, 113.48, 108.00.
MS (m/z,%): M–H2O, 268 (100), 240 (42), 205 (54), 152
(17).
2.2.10. N-(4-Methoxyphenyl)-5-chloro-furan-2-
carboxamidoxime (3l)
Yield: 22%. M.p. 141–143 °C. Rf: 0.32 (hexane:ethyl ace-
tate; 3:2). IR (KBr, m: cmÀ1): 3363 (N–H), 3191–3155
(broad, NOH), 1641 (C@N). 1H NMR (300 MHz,
CDCl3 + DMSO-d6): d 10.34 (s, 1H, NOH), 7.28 (s, 1H,
NH), 6.75 (dd, J = 9.3 6.7 Hz, 4H), 6.25 (d, J = 3.5 Hz,
1H), 6.16 (d, J = 3.2 Hz, 1H), 3.80 (s, 3H, OCH3). 13C
NMR (75 MHz, CDCl3 + DMSO-d6): d 155.97, 145.14,
143.39, 136.72, 133.19, 123.56, 114.04, 113.55, 107.74,
55.42. MS (m/z,%): M–H2O, 248 (100), 233 (54), 220
(14), 205 (28).
2.3. Synthesis of oxadiazaboroles
2.3.1. 4,5-Diphenyl-3-(5-chloro-2-thienyl)-4,5-dihydro-
1,2,4,5-oxadiazaborole (5a)
2.2.11. N-(4-Chlorophenyl)-5-chloro-furan-2-
carboxamidoxime (3m)
A mixture of N-phenyl-(5-chloro-thiophene)-2-carbo-
xamidoxime (3a) (150 mg, 0.68 mmol) and phenylboronic
acid (4) (92 mg, 0.76 mmol) in toluene (10 mL) was
refluxed under an inert atmosphere in the presence of
Yield: 30%. M.p. 142–144 °C. Rf: 0.29 (hexane:ethyl ace-
tate; 3:1). IR (KBr, m: cmÀ1): 3382 (N–H), 3127–3094
(broad, NOH), 1622 (C@N). 1H NMR (300 MHz,
CDCl3 + DMSO-d6): d 10.60 (s, br, 1H, NOH), 7.63 (s,
1H, NH), 7.14 (d, J = 8.7 Hz, 2H), 6.65 (d, J = 8.7 Hz,
2H). 13C NMR (75 MHz, CDCl3 + DMSO-d6): d 145.00,
141.81, 139.15, 137.11, 128.67, 127.10, 121.26, 113.59,
108.00. MS (m/z,%): M–H2O, 254 (100), 183 (22), 155
(31), 127 (75).
˚
molecular sieves (4 A) overnight. After extracted with ace-
tone and filtering, the solvent was evaporated under
reduced pressure. The crude product was crystallized from
hexane–ethylacetate mixture to give 5a as colorless needles,
140 mg, Yield: 67%. M.p. 164–166 °C. Rf: 0.41 (hex-
ane:ethyl acetate; 3:2). IR (KBr, mmax: cmÀ1): 1601
(C@N), 1452 (B–N), 1372 (B–O), 1109, 767, 701. 1H
NMR (CDCl3, 300 MHz): d 7.53–7.49 (m, 5H), 7.40–7.38
(m, 2H), 7.34–7.24 (m, 4H), 6.70 (dd, J = 4.10 Hz,
2.05 Hz, 1H), 6.53 (dd, J = 4.10 Hz, 2.05 Hz, 1H). 13C
NMR (CDCl3, 75 MHz) d: 155.51, 136.92, 134.36,
134.01, 131.44, 130.30, 129.64, 129.05, 128.68, 128.29,
126.68, 125.49. 11B NMR (160.46 MHz, CDCl3–15%
BF3 Á Et2O): d 32.3. MS (m/z,%): 338 (M+,100), 234 (15),
179 (20), 103 (11), 91 (7), 77 (15), 51 (6); HRMS calcd
for C17H12BN2OSCl: 338.0452; found: 338.0460.
2.2.12. N-(4-Bromophenyl)-5-chloro-furan-2-
carboxamidoxime (3n)
Yield: 44%. M.p. 163–164 °C. Rf: 0.66 (hexane:ethyl ace-
tate; 3:1). IR (KBr, m: cmÀ1): 3382 (N–H), 3087–2970
(broad, NOH), 1625 (C@N). 1H NMR (300 MHz,
CDCl3 + DMSO-d6): d 10.57 (s, 1H, NOH), 8.20 (s, 1H,
NH), 7.20 (d, J = 6.4 Hz, 2H), 6.60 (d, J = 7.3 Hz, 2H),
6.55 (dd, J = 3.5 1.1 Hz, 1H), 6.30 (dd, J = 3.2, 1.1 Hz,

1002
Y. Du¨ru¨st et al. / Polyhedron 27 (2008) 999–1007
2.3.2. 5-Phenyl-3-(2-thienyl)-4-(4-methylphenyl)-4,5-
dihydro-1,2,4,5-oxadiazaborole (5b)
2.3.6. 4-(4-Chlorophenyl)-5-phenyl-3-(5-chloro-2-thienyl)-
4,5-dihydro-1,2,4,5- oxadiazaborole (5f)
Yield: 45%. M.p. 222–224 °C (hexane:ethyl acetate). Rf:
0.54 (hexane:ethyl acetate; 3:2). IR (KBr, mmax: cmÀ1):
1604, 1566, 1514 (C@N), 1444 (B–N), 1369 (B–O), 1121,
M.p. 158–160 °C (hexane) (75%). Rf: 0.50 (hexane:ethyl
acetate; 3:2). IR (KBr, mmax: cmÀ1): 1600, 1571, 1525
(C@N), 1493, 1449 (B–N), 1370 (B–O), 1093, 829, 701.
1H NMR (300 MHz, CDCl3): d 7.49–7.40 (m, 6H), 7.31–
7.25 (m, 4H), 6.66 (dd, J = 5.0, 1.76 Hz, 1H), 6.58 (dd,
J = 3.9, 1.46 Hz, 1H). 13C NMR (75 MHz, CDCl3): d
155.23, 135.51, 135.23, 134.31, 131.61, 130.54, 129.96,
129.19, 128.40, 126.81, 125.08. 11B NMR (160.46 MHz,
1
1024, 822, 724. H NMR (CDCl3, 300 MHz): d 7.54 (d,
J = 7.91 Hz, 2H) 7.43–7.17 (m, 8H), 6.92–6.89 (m, 1H),
6.82 (d, J = 3.51 Hz, 1H), 2.46 (s, 3H). 13C NMR
(100 MHz, CDCl3): d 156.31, 138.79, 134.36, 134.16,
131.02, 130.40, 129.36, 128.64, 128.23, 127.99, 127.20,
126.73, 21.33. 11B NMR (160.46 MHz, CDCl3–15%
BF3 Á Et2O):d 32.4. MS (m/z,%): 318 (M+,100), 214 (15),
193 (23), 116 (7), 105 (8), 91 (5), 77 (8); HRMS calcd for
C18H15BN2OS: 318.0998; found: 318.1002.
CDCl3–15% BF3 Á Et2O):
d 32.2. MS (m/z,%): 372
(M+,100), 268 (14), 233 (9), 213 (26), 137 (15), 125 (11),
96 (12), 77 (14), 51 (5). HRMS calcd for C17H11BN2OSCl2:
372.0062; found: 372.0056.
2.3.3. 4-(4-Methylphenyl)-5-phenyl-3-(5-chloro-2-thienyl)-
4,5-dihydro-1,2,4,5-oxadiazaborole (5c)
2.3.7. 4-(4-Bromophenyl)-5-phenyl-3-(5-chloro-2-thienyl)-
4,5-dihydro-1,2,4,5-oxadiazaborole (5g)
Yield: 65%. M.p. 210–212 °C (hexane). Rf: 0.38 (hex-
Yield: 75%. M.p. 177–179 °C (hexane–ethyl acetate). Rf:
0.61 (hexane:ethyl acetate; 3:2). IR (KBr, mmax: cmÀ1):
1602, 1568, 1510 (C@N), 1488, 1455 (B–N), 1366 (B–O),
ane:ethyl acetate; 2:1). IR (KBr, m: cmÀ1): 1600, 1572,
1
1514 (C@N), 1452 (B–N), 1369 (B–O), 1111, 823, 698. H
1
NMR (300 MHz, CDCl3): d 7.98–6.55 (m, 11H), 2.20 (s,
3H). 13C NMR (CDCl3, 75 MHz): d 155.18, 139.08,
134.18, 133.93, 133.71, 133.20, 131.12, 130.64, 129.25,
128.83, 128.01, 127.95, 127.39, 126.59, 125.24, 122.04,
21.27. 11B NMR (160.46 MHz, CDCl3–15% BF3 Á Et2O):
d 32.2 MS (m/z,%): 352 (M+,100), 248 (11), 193 (25), 116
(11), 105 (8), 77 (11). HRMS calcd for C18H14BN2OSCl:
352.0608; found: 352.0626.
1105, 1073, 941, 835, 695. H NMR (CDCl3, 300 MHz):
d 7.65 (d, J = 0.88 Hz, 1H), 7.63 (m, 1H), 7.49–7.26 (m,
6H), 7.22 (d, J = 0.88 Hz, 1H), 7.20 (m, 1H), 6.74 (dd,
J = 2.34, 1.17 Hz, 1H), 6.56 (dd, J = 2.34, 1.17 Hz, 1H).
13C NMR (75 MHz, CDCl3): d 155.15, 136.04, 134.32,
133.53, 131.62, 130.28, 129.21, 128.41, 126.84, 125.07,
123.23. 11B NMR (160.46 MHz, CDCl3–15% BF3 Á Et2O):
d 32.3. MS (m/z,%): 418 (M+,100), 314 (12), 257 (14),
181 (8), 169 (8), 143 (12), 102 (18), 90 (12), 77 (15), 63
(8), 51 (8). HRMS calcd for C17H11BN2OSBrCl:
415.9557; found: 415.9567.
2.3.4. 4-(4-Methoxyphenyl)-5-phenyl-3-(2-thienyl)-4,5-
dihydro-1,2,4,5-oxadiazaborole (5d)
Yield: 70%. M.p. 161–163 °C (hexane–ethylacetate). Rf:
0.15 (hexane:ethyl acetate; 3:2). IR (KBr, mmax: cmÀ1):
1610, 1570, 1515 (C@N), 1444 (B–N), 1370 (B–O), 1256,
2.3.8. 4-(4-Iodophenyl)-5-phenyl-3-(5-chloro-2-thienyl)-
4,5-dihydro-1,2,4,5-oxadiazaborole (5h)
1
1030, 841, 705. H NMR (300 MHz, CDCl3): d 7.55 (d,
Yield: 52%. M.p. 184–186 °C (hexane–ethyl acetate). Rf:
0.50 (hexane:ethyl acetate; 3:2). IR (KBr, mmax: cmÀ1):
1603, 1597, 1508 (C@N), 1485, 1455 (B–N), 1368 (B–O),
J = 7.32 Hz, 4H), 7.40–7.21 (m, 4H), 7.00–6.86 (m, 4H),
3.89 (s, 3H). 13C NMR (75 MHz, CDCl3): d 159.86,
156.70, 134.38, 131.30, 129.79, 129.59, 128.96, 128.26,
127.49, 126.92, 115.15, 55.79. 11B NMR (160.46 MHz,
1
1103, 942, 829, 695. H NMR (300 MHz, CDCl3): d 7.83
(d, J = 7.6 Hz, 2H), 7.49–7.25 (m, 6H), 7.07 (d,
J = 7.6 Hz, 2H), 6.74 (d, J = 3.5 Hz, 1H), 6.55 (d,
J = 3.4 Hz, 1H). 13C NMR (75 MHz, CDCl3): d 155.10,
139.49, 136.72, 134.32, 134.27, 131.62, 130.49, 129.23,
128.41, 126.86, 125.05, 94.76. 11B NMR (160.46 MHz,
CDCl3–15% BF3 Á Et2O):
d 32.2. MS (m/z,%): 334
(M+,100), 230 (6), 216 (25), 209 (30), 194 (12), 121 (15),
77 (9). HRMS calcd for C18H15BN2O2S: 334.0947; found:
334.0978.
CDCl3–15% BF3 Á Et2O):
d 32.2. MS (m/z,%): 464
2.3.5. 4-(4-Methoxyphenyl)-5-phenyl-3-(5-chloro-2-
thienyl)-4,5-dihydro-1,2,4,5-oxadiazaborole (5e)
(M+,100), 360 (12), 305 (26), 229 (7), 198 (7), 151 (9),
102 (15), 90 (17), 77 (11), 63 (7). HRMS calcd for
C17H11BN2OSClI: 463.9418; found: 463.9409.
M.p. 169–170 °C (66%) (hexane–ethylacetate). Rf: 0.29
(hexane:ethyl acetate; 2:1). IR (KBr, m: cmÀ1): 1610, 1514
(C@N), 1454 (B–N), 1369 (B–O), 1255, 839, 700. 1H
NMR (300 MHz, CDCl3): d 7.54–6.60 (m, 11H), 3.84 (s,
3H, OCH3). 13C NMR (75 MHz, CDCl3): d 159.82,
155.44, 134.22, 133.99, 134.40, 131.17, 129.38, 128.92,
128.84, 128.07, 127.44, 126.60, 125.28, 115.12, 55.56. 11B
NMR (160.46 MHz, CDCl3–15% BF3 Á Et2O): d 32.2. MS
(m/z,%): 368 (M+,100), 264 (6), 249 (16), 209 (34), 194
(16), 121 (16), 77 (12). HRMS calcd for C18H14BN2O2SCl:
368.0558; found: 368.0575.
2.3.9. 4-(1-Naphthyl)-5-phenyl-3-(5-chloro-2-thienyl)-4,5-
dihydro-1,2,4,5-oxadiazaborole (5i)
Yield: 46%. M.p. 132–134 °C (hexane–ethyl acetate). Rf:
0.54 (hexane:ethyl acetate; 3:2). IR (KBr, mmax: cmÀ1):
1599, 1522, 1508 (C@N), 1434 (B–N), 1369 (B–O), 1106,
800, 776, 696. 1H NMR (300 MHz, CDCl3): d 8.06 (d,
J = 7.9 Hz, 1H), 8.00 (d, J = 7.9 Hz, 1H), 7.74–7.16 (m,
11H), 6.53 (dd, J = 1.76, 0.88 Hz, 1H), 6.39 (dd, J = 1.76,
0.88 Hz, 1H). 13C NMR (CDCl3, 75 MHz): d 156.11,

Y. Du¨ru¨st et al. / Polyhedron 27 (2008) 999–1007
1003
134.57, 134.22, 133.89, 133.13, 131.48, 131.11, 130.19,
128.90, 128.68, 128.28, 128.24, 127.46, 126.79, 126.62,
125.99, 125.23, 122.52. 11B NMR (160.46 MHz, CDCl3–
15% BF3 Á Et2O): d 32.8. MS (m/z,%): 388 (M+,100), 249
(26), 229 (69), 153 (25), 140 (18), 126 (11), 115 (12),
77(9), 51 (5). HRMS calcd for C21H14BN2OSCl:
388.0608; found: 388.0607.
1611, 1530 (C@N), 1496 (B–N), 1373 (B–O), 1139, 1092,
1021, 838, 789, 704. 1H NMR (300 MHz, CDCl3): d
7.49–7.26 (m, 10H), 6.12 (dd, J = 3.33 Hz, 1.76 Hz,
1.46,1H), 5.98 (dd, J = 3.52 Hz, 1.76 Hz, 1.46 Hz, 1H).
13C NMR (CDCl3, 75 MHz): d 152.38, 139.88, 135.60,
135.03, 134.36, 131.63, 130.36, 129.65, 128.39, 115.91,
108.33. 11B NMR (160.46 MHz, CDCl3–15% BF3 Á Et2O):
d 32.1. MS (m/z,%): 356 (M+,100), 319 (7), 293 (15), 257
(12), 213 (25), 200 (25), 189 (38), 162 (9), 137 (40), 102
(25), 77 (20), 64 (8), 51(9). HRMS calcd for
C17H11BN2O2Cl2: 356.0291; found: 356.0270.
2.3.10. 3-(5-Chloro-2-furyl)-4,5-diphenyl-4,5-dihydro-
1,2,4,5-oxadiazaborole (5j)
Yield: 50%. M.p. 114–116 °C (benzene–petroleum ether).
Rf: 0.29 (hexane:ethyl acetate; 3:1). IR (KBr, mmax: cmÀ1):
1598, 1534 (C@N), 1498, 1484 (B–N), 1375 (B–O), 1138,
2.3.14. 4-(4-Bromophenyl)-3-(5-chloro-2-furyl)-5-phenyl-
4,5-dihydro-1,2,4,5-oxadiazaborole (5n)
1
1024, 790, 699. H NMR (300 MHz, CDCl3): d 7.52–7.23
(m, 11H), 6.07 (dd, J = 2.34, 1.17 Hz, 1H), 5.87 (dd,
J = 3.66, 1.17, 0.88 Hz, 1H). 13C NMR (75 MHz, CDCl3):
d 152.63, 140.20, 139.68, 136.99, 134.40, 131.45, 130.15,
129.20, 128.30, 128.27, 115.70, 108.22. MS (m/z,%): 322
(M+,100), 285 (15), 258 (31), 179 (18), 166 (35), 154 (44),
128 (15), 103 (35), 77 (34), 64 (10), 51 (13). HRMS calcd
for C17H12BN2O2Cl: 322.0680; found: 322.0709.
Yield: 72%. M.p. 166–168 °C (hexane–ethyl acetate). Rf:
0.66 (hexane:ethyl acetate; 3:2). IR (KBr, mmax: cmÀ1):
1610, 1530 (C@N), 1492 (B–N), 1374 (B–O), 1210, 1140,
1
1020, 789, 704. H NMR (300 MHz, CDCl3): d 7.65 (m,
10H), 6.13 (d, J = 3.22 Hz, 1H), 5.99 (dd, J = 1.76,
0.88 Hz, 1H). 13C NMR (75 MHz, CDCl3): d 152.30,
139.92, 139.84, 136.12, 134.37, 133.35, 131.64, 129.96,
128.40, 123.08, 115.90, 108.33. 11B NMR (160.46 MHz,
2.3.11. 3-(5-Chloro-2-furyl)-5-phenyl-4-(4-methylphenlyl)-
4,5-dihydro-1,2,4,5-oxadiazaborole (5k)
CDCl3–15% BF3 Á Et2O):
d 32.0. MS (m/z,%): 402
(M+,100), 257 (29), 244 (15), 232 (26), 181 (18), 154 (8),
127 (15), 102 (40), 90 (12), 77 (26), 63 (9), 51 (9). HRMS
calcd for C17H11BN2O2BrCl: 399.9785; found: 399.9796.
Yield: 60%. M.p. 167–168 °C (benzene–petroleum
ether). Rf: 0.23 (hexane:ethyl acetate; 3:1). IR (KBr, mmax
:
cmÀ1): 1611, 1532, 1515 (C@N), 1485 (B–N), 1376 (B–O),
1
1138, 1028, 831, 794, 707. H NMR (300 MHz, CDCl3):
2.3.15. 3-(5-Chloro-2-furyl)-4-(4-iodophenyl)-5-phenyl-4,5-
dihydro-1,2,4,5-oxadiazaborole (5o)
d 7.53 (d, J = 7.32 Hz, 2H), 7.41–7.26 (m, 5H), 7.19 (d,
J = 7.32 Hz, 2H), 7.03 (d, J = 8.50 Hz, 1H), 6.77 (d,
J = 8.20 Hz, 1H) 2.46 (s, 3H). 13C NMR (100 MHz,
CDCl3): d 152.55, 140.15, 139.42, 138.94, 134.19, 134.10,
131.15, 130.49, 129.64, 128.01, 127.79, 122.80, 115.43,
107.93, 21.29. MS (m/z,%): 336 (M+,100), 299 (15), 271
(10), 192 (23), 180 (23), 168 (54), 142 (8), 127 (7), 116
(28), 104 (10), 90 (15), 77 (20), 65 (8), 51 (8). HRMS calcd
for C18H14BN2O2Cl: 336.0837; found: 336.0868.
Yield: 75%. M.p. 203–205 °C (hexane–ethyl acetate). Rf:
0.58 (hexane:ethyl acetate; 3:2). IR (KBr, mmax: cmÀ1):
1
1627, 1583 (C@N), 1482 (B–N), 1367 (B–O), 978, 671. H
NMR (300 MHz, CDCl3): d 7.83 (d, J = 1.17 Hz, 1H),
7.81 (s, 1H), 7.50–7.24 (m, 6H), 7.08 (d, J = 1.17 Hz,
1H), 7.06 (s, 1H), 6.13 (dd, J = 2.34, 1.17 Hz, 1H), 5.99
(dd, J = 2.34, 1.17 Hz, 1H). 13C NMR (75 MHz, CDCl3):
d 152.27, 139.93, 139.83, 139.31, 136.81, 134.37, 131.63,
130.16, 128.39, 115.92, 108.32, 94.45. 11B NMR
(160.46 MHz, CDCl3–15% BF3 Á Et2O): d 32.0. MS (m/
z,%): 448 (M+,100), 305 (20), 292 (23), 280 (39), 257
(23), 229 (16), 203 (7), 189 (9), 154 (11), 127 (16), 102
(41), 90 (16), 77 (19), 63 (13), 51(9). HRMS calcd for
C17H11BN2O2ClI: 447.9647; found: 447.9683.
2.3.12. 3-(5-Chloro-2-furyl)-4-(4-methoxyphenyl)-5-
phenyl-4,5-dihydro-1,2,4,5-oxadiazaborole (5l)
Yield: 65%. M.p. 145–147 °C (hexane–ethyl acetate). Rf:
0.32 (hexane:ethyl acetate; 3:1). IR (KBr, mmax: cmÀ1):
1612, 1516 (C@N), 1489 (B–N), 1375 (B–O), 1251, 1023,
1
841, 794, 707. H NMR (300 MHz, CDCl3): d 7.45–6.90
(m, 10H), 6.00 (dd, J = 3.52, 1.76 Hz, 1H), 5.70 (dd,
J = 3.52, 1.76 Hz, 1H) 3.81 (s, 3H). 13C NMR (75 MHz,
CDCl3): d 159.91, 152.92, 140.36, 139.62, 134.40, 131.43,
129.49, 129.34, 128.28, 115.71, 108.26, 55.83. 11B NMR
(160.46 MHz, CDCl3–15% BF3 Á Et2O): d 32.0. MS (m/
z,%): 352 (M+,100), 209 (27), 194 (16), 184 (30), 133
(21), 121 (10), 103 (11), 90 (13), 77 (15). HRMS calcd for
C18H14BN2O3Cl: 352.0786; found: 352.0800.
2.3.16. 3-(5-Chloro-2-furyl)-4-(1-naphthyl)-5-phenyl-4,5-
dihydro-1,2,4,5-oxadiazaborole (5p)
Yield: 40%. M.p. 148–150 °C (hexane–dichloroethane).
Rf: 0.49 (hexane:ethyl acetate; 3:2). IR (KBr, mmax: cmÀ1):
1603, 1527 (C@N), 1484 (B–N), 1371 (B–O), 1209, 1143,
1
1018, 777, 710. H NMR (300 MHz, CDCl3): d 8.03 (d,
J = 8.03 Hz, 1H), 7.98 (d, J = 8.03 Hz, 1H), 7.69–7.12
(m, 11H), 5.87 (s, 1H), 5.39 (s, 1H). 13C NMR (75 MHz,
CDCl3): d 153.08, 140.00, 139.55, 134.49, 134.26, 133.24,
131.50, 130.79, 129.86, 128.79, 128.26, 125.15, 127.41,
126.27, 125.93, 122.52, 115.32, 108.23. MS (m/z,%): 372
(M+,69), 336 (92), 308 (42), 292 (15), 259 (34), 233 (48),
216 (54), 204 (100), 189 (15), 178 (17), 153 (54), 140 (34),
2.3.13. 4-(4-Chlorophenyl)-3-(5-chloro-2-furyl)-5-phenyl-
4,5-dihydro-1,2,4,5- oxadiazaborole (5m)
M.p. 131–133 °C (hexane–dichloroethane) (43%). Rf:
0.29 (hexane:ethyl acetate; 3:1). IR (KBr, mmax: cmÀ1):

1004
Y. Du¨ru¨st et al. / Polyhedron 27 (2008) 999–1007
126 (29), 115 (23), 77 (18), 51 (8). HRMS calcd for
C21H14BN2O2Cl: 372.0837; found: 372.0824.
149.35, 134.20, 134.01, 131.24, 129.94, 128.82, 128.09,
127.57, 127.44, 122.90, 122.40, 120.74. 11B NMR
(160.46 MHz, CDCl3–15% BF3 Á Et2O): d 32.4. MS (m/
z,%): 299 (M+,100), 222 (8), 195 (11), 179 (31), 118 (8),
91 (11), 77 (15), 51 (9). HRMS calcd for C18H14BN3O:
299.1230; found: 299.1247.
2.3.17. 3-(2-Pyridyl)-4-methyl-5-phenyl-4,5-dihydro-
1,2,4,5-oxadiazaborole (5q)
Yield: 28%. M.p. 76–77 °C hexane–petroleum ether. Rf:
0.18 (hexane:ethyl acetate; 1:3). IR (KBr, m: cmÀ1): 1607,
1587, 1542 (C@N), 1482 (B–N), 1391 (B–O), 1297, 1081,
2.3.21. 3-(4-Pyridyl)-4-(4-methylphenyl)-5-phenyl-4,5-
dihydro-1,2,4,5-oxadiazaborole (5u)
1
793, 697. H NMR (300 MHz, CDCl3): d 8.78–7.44 (m,
9H), 3.67 (s, 3H).13C NMR, (75 MHz, CDCl3) d: 160.05,
149.24, 147.50, 137.07, 133.88, 130.72, 128.27, 124.76,
124.73, 31.43. 11B NMR (160.46 MHz, CDCl3–15%
BF3 Á Et2O): d 33.2. MS (m/z,%): 236 (M+,100), 160 (9),
133 (25), 105 (100), 78 (29), 51(10). HRMS calcd for
C13H12BN3O: 237.1073; found: 237.1075.
Yield: 80%. M.p. 234–236 °C (hexane–dichlorometh-
ane). Rf: 0.18 (hexane:ethyl acetate; 1:2). IR (KBr, mmax
:
cmÀ1): 1601, 1587, 1541 (C@N), 1483 (B–N), 1390 (B–O),
1
1076, 1020, 792, 694. H NMR (400 MHz, DMSO-d6): d
8.45 (d, J = 6.0 Hz, 1H), 8.12 (s, 1H), 7.84 (s, 1H), 7.76
(d, J = 6.5 Hz, 1H), 7.34–7.25 (m, 5H), 6.85 (d,
J = 8.1 Hz, 1H), 6.54 (d, J = 8.3 Hz, 1H), 2.16 (s, 3H).
2.3.18. 3-(2-Pyridyl)-4-ethyl-5-phenyl-4,5-dihydro-1,2,4,5-
oxadiazaborole (5r)
Yield: 63%. M.p. 82–83 °C (benzene–petroleum ether).
Rf: 0.11 (hexane:ethyl acetate; 2:1). IR (KBr, mmax: cmÀ1):
1600, 1552 (C@N), 1482 (B–N), 1348 (B–O), 1151, 777,
R2
R1
R3NH2
R2
Cl
NCS
DMF
NOH
NOH
NOH
HN
R3
H
1
715. H NMR (300 MHz, CDCl3): d 8.73–8.71 (m, 1H),
7.96–7.79 (m, 4H), 7.51–7.45 (m, 4H), 4.18 (q, 2H), 1.26
(t, 3H). 13C NMR (75 MHz, CDCl3): d 160.07, 149.54,
147.74, 137.29, 133.94, 130.95, 128.53, 124.96, 124.89,
38.40, 17.85. 11B NMR (160.46 MHz, CDCl3-15%
BF3 Á Et2O): d 33.2. MS (m/z,%): 250 (M+,54), 236 (8),
174 (52), 147 (31), 105 (100), 78 (40), 51 (11). HRMS calcd
for C14H14BN3O: 251.1230; found: 251.1237.
2
3
1
R3
R2
R1
a
b
c
2-Thienyl
2-Thienyl
2-Thienyl
5-Chloro-2-thienyl
2-Thienyl
Ph
4-Me-C6H4
4-Me-C6H4
5-Chloro-2-thienyl
2-Thienyl
4-MeO-C6H4
2-Thienyl
2-Thienyl
d
e
2.3.19. 3-(2-Pyridyl)-4-(1-naphthyl)-5-phenyl-4,5-dihydro-
1,2,4,5-oxadiazaborole (5s)
4-MeO-C6H4
4-Cl-C6H4
5-Chloro-2-thienyl
5-Chloro-2-thienyl
5-Chloro-2-thienyl
5-Chloro-2-thienyl
5-Chloro-2-thienyl
5-Chloro-2-furyl
Yield: 51%. M.p. 181–182 °C (hexane–petroleum ether).
Rf: 0.31 (hexane:ethyl acetate; 1:3). IR (KBr, m: cmÀ1):
1598, 1525 (C@N), 1473 (B–N), 1374 (B–O), 1151, 824,
768, 694. 1H NMR (400 MHz, CDCl3): d 8.20 (d,
J = 4.5 Hz, 1H), 7.76 (d, J = 7.7 Hz, 2H), 7.72 (d,
J = 8.4 Hz, 1H), 7.62 (d, J = 7.8 Hz, 1H), 7.56 (dt,
J = 1.7, 7.7, 15.5 Hz, 1H), 7.51–7.32 (m, 7H), 7.20 (t,
2H), 7.10 (ddd, J = 1.0, 4.8, 7.5 Hz, 1H). 13C NMR
(100 MHz, CDCl3): d 160.30, 149.25, 146.17, 136.32,
134.13, 134.10, 134.08, 131.07, 130.84, 128.44, 128.36,
128.29, 127.96, 127.10, 126.46, 125.87, 125.41, 124.37,
124.12, 122.71. 11B NMR (160.46 MHz, CDCl3–15%
BF3 Á Et2O): d 32.5. MS (m/z,%): 349 (M+,100), 318 (11),
272 (19), 244 (27), 229 (10), 141 (27), 115 (8), 78 (9). HRMS
calcd for C22H16BN3O: 349.1386; found: 349.1424.
f
2-Thienyl
2-Thienyl
2-Thienyl
g
4-Br-C6H4
4-I-C6H4
h
i
2-Thienyl
2-Furyl
1-Naphthyl
Ph
j
4-Me-C6H4
5-Chloro-2-furyl
2-Furyl
k
4-MeO-C6H4
4-Cl-C6H4
5-Chloro-2-furyl
5-Chloro-2-furyl
2-Furyl
2-Furyl
l
m
4-Br-C6H4
4-I-C6H4
5-Chloro-2-furyl
n
o
2-Furyl
2-Furyl
2-Furyl
5-Chloro-2-furyl
5-Chloro-2-furyl
1-Naphthyl
p
q
r
2-Pyridyl
2-Pyridyl
Me
2-Pyridyl
2-Pyridyl
2.3.20. 3-(4-Pyridyl)-4,5-diphenyl-4,5-dihydro-1,2,4,5-
oxadiazaborole (5t)
Et
Yield: 42%. M.p. 213–215 °C (hexane–ethyl acetate). Rf:
0.08 (hexane:ethyl acetate; 2:1). IR (KBr, mmax: cmÀ1):
1653, 1599 (C@N), 1516 (B–N), 1373 (B–O), 943, 823,
1-Naphthyl
2-Pyridyl
4-Pyridyl
4-Pyridyl
Ph
2-Pyridyl
4-Pyridyl
s
t
Ph
1
4-Me-C6H4
4-Me-C6H4
684. H NMR (300 MHz, CDCl3 + DMSO-d6): d 8.22 (d,
u
4-Pyridyl
Ph
J = 5.86 Hz, 1H), 8.18 (d, J = 5.56 Hz, 1H), 7.49 (d,
J = 7.33 Hz, 1H), 7.24–6.56 (m, 10H), 6.33 (d,
J = 7.62 Hz, 1H). 13C NMR (75 MHz, CDCl3): d 149.92,
v
Scheme 1. Structure of the N-substituted amidoximes.

Y. Du¨ru¨st et al. / Polyhedron 27 (2008) 999–1007
1005
R1
R1
N
HO
Toluene
O
NOH
+
B
N
Reflux
6-8 h
NH
R2
B
HO
R2
3
4
5
R2
R1
5-Chloro-2-furyl
R1
R2
5-Chloro-2-thienyl
5l
5a
5b
5c
Ph
4-MeO-C6H4
4-Me-C6H4
4-Me-C6H4
4-Cl-C6H4
4-Br-C6H4
4-I-C6H4
1-Naphthyl
Me
2-Thienyl
5m 5-Chloro-2-furyl
5-Chloro-2-furyl
5-Chloro-2-thienyl
2-Thienyl
5n
5-Chloro-2-furyl
5d
4-MeO-C6H4
4-MeO-C6H4
5o
5p
5-Chloro-2-thienyl
5-Chloro-2-thienyl
5-Chloro-2-thienyl
5-Chloro-2-thienyl
5-Chloro-2-thienyl
5-Chloro-2-furyl
5-Chloro-2-furyl
5e
5f
2-Pyridyl
4-Cl-C6H4
4-Br-C6H4
4-I-C6H4
1-Naphthyl
Ph
5q
5r
Et
5g
2-Pyridyl
2-Pyridyl
4-Pyridyl
4-Pyridyl
Ph
1-Naphthyl
5h
5i
5s
5t
Ph
5j
5u
5v
4-Me-C6H4
4-Me-C6H4
4-Me-C6H4
5-Chloro-2-furyl
5k
Scheme 2. Structure of the 1,2,4,5-oxadiazaboroles.
13C NMR (100 MHz, DMSO-d6): d 149.85, 148.37, 138.56,
134.45, 130.80, 130.20, 129.32, 128.57, 127.56, 122.45,
120.94, 20.68. 11B NMR (160.46 MHz, CDCl3–15%
BF3 Á Et2O): d 32.2. MS (m/z,%): 313 (M+,100), 298 (7),
208 (10), 193 (23), 104 (7), 91(9), 77 (8), 51(6). HRMS calcd
for C19H16BN3O: 313.1386; found: 313.1415.
2.3.22. 3,5-Diphenyl-4-(4-methylphenyl)-4,5-dihydro-
1,2,4,5-oxadiazaborole (5v)
Yield: 85%. M.p. 243–245 °C (hexane–ethyl acetate). Rf:
0.51 (hexane:ethyl acetate; 2:1). IR (KBr, mmax: cmÀ1):
1600, 1539, 1514 (C@N), 1438 (B–N), 1373 (B–O), 1028,
1
822, 698. H NMR (300 MHz, CDCl3): d 7.75–6.69 (m,
14H), 2.46 (s, 3H). 11B NMR (160.46 MHz, CDCl3–15%
BF3 Á Et2O): d 32.3. MS (m/z,%): 312 (M+,100), 297 (6),
208 (15), 193 (26), 104 (11), 91(12), 77 (15). HRMS calcd
for C20H17BN2O: 312.1434; found: 312.1460.
R1
b
R1
a
N
N
N
a
C
N
O
R2
R1
b
R1
N
C
R2
c
B
R2
N
c
O
N
B
R2
N
Ph
R2
B
Ph
Scheme 3.
Scheme 4.

1006
Y. Du¨ru¨st et al. / Polyhedron 27 (2008) 999–1007
Fig. 1. X-ray ORTEP view of 5r.
3. Results and discussion
roles in their 13C NMR spectra appeared to resonate in the
deshielded region at around 160–149 ppm. When there is a
2-pyridyl group on the number three carbon of the hetero-
cycle, the iminic carbon chemical shifts go to more
deshielded lowfield regions. In addition, the 11B NMR
spectra of these compounds were measured (the conditions
are given in Section 2) and the boron chemical shift fre-
quencies appear between 32.0 and 33.2 ppm, which can
be considered as an indication of a trigonal planar sp2
hybridized boron atom [26,27].
As for the electron impact mass spectra of the oxadiaz-
aboroles; peaks related to the following fragmentations:
diaziridine cation in route a, nitrilium cation in route b
and borimide cation in route c, would occur (Scheme 3).
Except for compounds 5p and 5r, all of the molecular
ion peaks have relative abundances of 100%, on account
of the following structure which has aromatic stability
(Scheme 4).
In a recent paper [11] we described the synthesis and
protonation equilibria of 4-unsubstituted 1,2,4,5-oxadiaz-
aboroles in non-aqueous media. In the present work we
report here the synthesis of some novel 3,4,5-trisubstituted
1,2,4,5-oxadiazaboroles bearing thiophene, furan and pyr-
idine at the 3-position of the heterocyclic ring. The N-
substituted amidoximes used as the starting compounds
were obtained as described in the literature [12–24]
(Scheme 1).
The new oxadiazaboroles 5a–v (Scheme 2) show strong
absorptions related to the B–N and B–O stretching vibra-
tions in the 1516–1438 and 1391–1348 cmÀ1 regions in their
IR spectra, which are remarkably consistent with the
reported values for B–O and B–N stretching frequencies
[25]. Iminic carbon chemical shifts of the title oxadiazabo-
As a representative view, the X-ray crystal structure and
selected atomic parameters are given for compound 5r
(Fig. 1, Tables 1 and 2).
Table 1
Crystallographic data for 3-(2-pyridyl)-4-ethyl-5-phenyl-4,5-dihydro-
1,2,4,5-oxadiazaborole (5r)
Empirical formula
Formula weight (amu)
Crystal color, habit
Crystal dimensions (mm)
Crystal system
C14H14BN3O
251.09
colorless, lath fragment
0.30 Â 0.07 Â 0.03
Table 2
˚
Orthorhombic
Pbca
Selected bond distances (A) and bond angles (°) with estimated standard
deviations of 3-(2-pyridyl)-4-ethyl-5-phenyl-4,5-dihydro-1,2,4,5-oxadiaz-
Space group
Cell parameters at T (K)
90
aborole (5r)
˚
a (A)
11.600 (2)
10.1778 (17)
21.602 (4)
2550.4 (8)
Bond distances
Bond angles
˚
b (A)
˚
c (A)
O1–B1
O1–N2
N1–C1
N1–B1
N1–C13
N2–C1
N3–C6
N3–C2
1.387 (2)
B1–O1–N2
O1–B1–N1
O1–B1–C7
N1–B1–C7
C1–N1–B1
C1–N1–C13
B1–N1–C13
C1–N2–O1
C6–N3–C2
N2–C1–N1
N2–C1–C2
N1–C1–C2
N3–C2–C3
N3–C2–C1
108.70 (11)
106.64 (13)
120.49 (14)
132.86 (14)
104.97 (12)
123.75 (13)
131.02 (13)
105.38 (11)
116.65 (13)
114.32 (13)
118.96 (13)
126.69 (13)
123.57 (14)
116.29 (13)
3
˚
V (A )
1.4370 (16)
1.3796 (19)
1.430 (2)
1.4764 (18)
1.3062 (19)
1.344 (2)
Z
8
Dcalc (Mg mÀ3
)
1.308
none
2.5–27.8
23865
3022
X = 2
Absorption correction
h Range for collection (°)
Number of reflections measured
Number of independent reflections
Observed reflections
1.3492 (19)
[I > Xr(I)]
Refinement method
Final R indices [I > Xr(I)]
2142
full matrix least squares on F2
X = 2
R[F2 > 2r(F2)] = 0.049
wR(F2) = 0.097

Y. Du¨ru¨st et al. / Polyhedron 27 (2008) 999–1007
[5] A. Suzuki, Pure Appl. Chem. 66 (1994) 213.
1007
Acknowledgements
[6] N. Miyaura, A. Suzuki, Chem. Rev. 95 (1995) 2457.
[7] A. Dornow, K. Fischer, Chem. Ber. 99 (1966) 68.
[8] A.B. Goel, V.D. Gupta, J. Indian Chem. Soc. 54 (1977) 581.
[9] (a) H.L. Yale, J. Heterocycl. Chem. 8 (1971) 205;
(b) H.L. Yale, J. Heterocycl. Chem. 8 (1971) 193.
_
Abant Izzet Baysal University, Research Fund (BAP
Grant No. 2006.03.03.249) for financial assistance and
Dr. F.R. Fronczek (Lousiana State University, Baton
Rouge, LA, USA) for X-ray diffraction data are gratefully
acknowledged.
[10] P.I. Paetzold, G. Stohr, Chem. Ber. 101 (1968) 2874.
[11] Y. Durust, N. Durust, M. Akcan, J. Chem. Eng. Data 52 (2007) 718.
¨ ¨ ¨ ¨
[12] Y. Durust, C. Altug˘, F. Kılıßc, Phosphorus Sulfur Silicon 182 (2007)
¨ ¨
299.
Appendix A. Supplementary material
_
[13] N. Durust, Y. Durust, I. Merißc, Turk. J. Chem. 26 (2002) 833.
[14] Y. Durust, F. Nohut, Synth. Commun. 29 (1999) 1997.
¨ ¨
¨ ¨
¨ ¨
[15] H. Ag˘ırbaßs, Y. Durust, D. Sumengen, Phosphorus Sulfur Silicon 66
¨ ¨
¨
CCDC data_MA50 contains the supplementary crystal-
lographic data for 5r. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.
html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.poly.2007.11.043.
(1992) 321.
[16] Y. Du¨ru¨st, N. Du¨ru¨st, Synth. Commun. 22 (1992) 209.
[17] Y. Durust, H. Ag˘ırbaßs, D. Sumengen, Phosphorus Sulfur Silicon 62
¨ ¨
¨
(1991) 47.
[18] T.L. Deegan, T.J. Nitz, D. Cebzanov, D.E. Pufko, J.A. Porco Jr.,
Bioorg. Med Chem. Lett. 9 (1999) 209.
[19] J.B. Hynes, R.F. Gratz, J. Med. Chem. 15 (1972) 198.
[20] H.A. Oskooie, M.M. Heravi, Z. Jaddi, Phosphorus Sulfur Silicon 180
(2005) 1993.
[21] K. Niknam, B. Karami, A.R. Kiasat, Bull. Korean Chem. Soc. 26
(2005) 975.
[22] N. Iranpoor, H. Firouzabadi, G. Aghapour, Synth. Commun. 32
(2002) 2535.
References
[23] S. Chandrasekhar, K. Gopalaiah, Tetrahedron Lett. 42 (2001) 8123.
[24] T. L Ho, C.M. Wong, Synth. Commun. 5 (1975) 299.
[25] B. Stuart, Infrared Spectroscopy: Fundamentals and Applications,
John & Wiley Sons, Inc., Hoboken, NJ, 2004, p. 83.
[26] W. Kliegel, G. Lubkowitz, J.O. Prokriefke, S.J. Rettig, J. Trotter,
Can. J. Chem. 79 (2001) 26.
[1] D.N. Nicolaides, E.A. Varella, in: S. Patai (Ed.), The Chemistry of
Acid Derivatives, vol. 2, Suppl. B, John Wiley & Sons Ltd., 1992, p.
875.
[2] F. Eloy, R. Lenaers, Chem. Rev. 62 (1962) 55.
[3] K.S. Webb, D. Levy, Tetrahedron Lett. 36 (1995) 5117.
[4] C. Thiebes, G.K.S. Prakash, N.A. Petasis, G. Olah, Synlett (1998)
141.
[27] S. Hermanek, Chem. Rev. 92 (1992) 325.