General Papers
ARKIVOC 2016 (vi) 144-151
0.00 ppm). The mass spectra (ESI-MS) were recorded on Micromass LCT KC-455 instrument
using electron spray positive ion mode.
General reaction procedure for the synthesis of dipyrromethanes
Aldehyde (20 mmol, 1 equiv.) was added to aqueous solution of boric acid (248 mg in 10 ml of
water) followed by dropwise addition of pyrrole (3.35 g, 50 mmol). The reaction mixture was
stirred on a magnetic stirrer in an open atmosphere at 30°C and the progress of the reaction was
monitored by TLC. After completion of the reaction (when aldehyde was consumed, as checked
by TLC), the organic layer was separated and aqueous layer was extracted with dichloromethane,
the combined organic layers were dried over anhydrous Na2SO4 and purified by column
chromatography over silica gel (60-120 mesh) using petroleum ether-chloroform (ratio varied with
product) to give corresponding dipyrromethanes respectively. The spectral data of the compounds
are reported below:
Dipyrromethane (3a). Greyish solid, mp 73 °C (lit.11 mp 75 °C, lit. yield11 41%). 1H NMR (300
MHz, CDCl3): 3.92 (s, 2H), 6.02 (s, 2H), 6.14 (d, J 2.4 Hz, 2H), 6.64 (s, 2H), 7.83 (s, 2H, NH).
MS m/z (%): 146 [M]+ (100) calc. for C9H10N2.
meso-Phenyldipyrromethane (3b). White crystals, mp 100 °C (lit.11 mp 100-101 °C, lit. yield11
53%). 1H NMR (300 MHz, CDCl3): 5.48 (s, 1H), 5.92 (s, 2H), 6.16 (q, 2H), 6.70 (d, 2H), 7.21-
7.32 (m, 5H), 7.92 (brs, 2H). MS m/z (%): 222 (M+, 97), (M+_ C6H5, 100) calc. for C15H14N2.
meso-Chlorophenyldipyrromethane (3c). Pale yellow solid, mp 110 °C (lit.13 mp 112-113 °C,
lit. yield13 44%). 1H NMR (300 MHz, CDCl3): 5.44 (s, 1H), 5.88 (m, 2H), 6.24 (m, 2H), 6.70 (m,
2H), 7.24-7.29 (m, 2H), 7.93 (brs, 2H, NH). MS m/z (%): 256 (M+, 43), 258 (M+2)+, 14), 145 (M+_
C6H4Cl, 100) calc. for C15H13ClN2.
meso-Fluorophenyldipyrromethane (3d). White crystals, mp 81 °C (lit.11 mp 81 °C, lit. yield11
28%). 1H NMR (300 MHz, CDCl3): 5.49 (s, 1H), 5.93 (m, 2H), 6.20 (dd, J 2.8 Hz, 2H), 6.74 (m,
2H), 7.04 (m, 2H), 7.94 (m, 2H), 8.18 (brs, 2H, NH). MS m/z (%): 240 (M+, 100), 145 (M+_ C6H4F,
45) calculated for C15H13FN2.
meso-Bromophenyldipyrromethane (3e). White solid, mp 122 °C (lit.13 mp 122-123 °C, lit.
yield13 20%). 1H NMR (300 MHz, CDCl3): 5.43 (s, 1H), 5.86 (s, 2H), 6.15 (dd, J 4.5 Hz, 2H), 6.68
(d, J 8.2 Hz, 2H), 7.10-7.24 (m, 4H), 7.92 (brs, 2H, NH). MS m/z (%): 301 (M+, 100), 303 [(M+2)+,
98], 112 (M+_ C6H4Br, 80) calculated for C15H13BrN2.
meso-Nitrophenyldipyrromethane (3f). Yellow solid, mp 159 °C (lit.11 mp 159-160 °C, lit.
yield11 56%). 1H NMR (300 MHz, CDCl3): 5.58 (s, 1H), 5.87 (s, 2H), 6.17 (dd, J 4.4 Hz, 2H), 6.75
(d, J 4.8 Hz, 2H), 7.37-8.02 (m, 4H), 8.17 (brs, 2H, NH). MS m/z (%): 267 (M+, 100), 145 (M+_
C6H4NO2, 80) calculated for C15H13N3O2.
1
meso-Tolyldipyrromethane (3g). Buff solid, mp 112 °C (lit.11 mp 114 °C, lit. yield11 33%), H
NMR (300 MHz, CDCl3): 2.35 (s, 3H, CH3), 5.44 (s, 1H), 5.92 (s, 2H), 6.15 (dd, J 4.2 Hz, 2H),
6.83 (d, J 4.8 Hz, 2H), 7.05-7.16 (m, 4H), 7.91 (brs, 2H, NH). MS m/z (%): 236 (M+, 15), 221
(M+_ CH3, 3) calculated for C16H16N2.
meso-Mesityldipyrromethane (3h). Pale yellow solid. mp 170 °C (lit,11 mp 170-171 °C, lit.
yield11 27%), 1H NMR (300 MHz, CDCl3): 2.04 (s, 6H, CH3), 2.27 (s, 3H, CH3), 5.92 (s, 1H), 6.03
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