Such a mechanism was experimentally proved in a number of previous works4,13f,17 where the similar intermediate O-vinyloximes were isolated and separately rearranged to the corresponding pyrroles.
In summary, the reaction of oximes of aromatic ketones with phenylacetylene in MOH- DMSO systems paves a new path to one-pot preparation of di- and triarylpyrroles – promising precursors of pharmaceutically important compounds and optoelectronic materials.
Experimental Section
General Procedures. IR spectra were recorded from .Br pellets on a Bruker IFS-25 instrument. NMR spectra were run on a Bruker DPX 400 spectrometer [400.13 (1H) MHz, 100.6 MHz (13.)]; .DCl3 as solvent, HMDS as internal standard. Detailed 13C NMR peak assignments were obtained by careful analysis of HSQC and HMBC 2D NMR spectra. GCMS spectrum was run on a MSD5975C (Agilent), microanalyses were obtained in the A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Russia on an EA FLASH 1112 Series (CHN Analyzer) instrument.
2,5-Diphenyl-1H-pyrrole (4). The oxime 1 (20.41 g, 0.151 mol) and LiOH (3.61 g, 0.151 mol) were dissolved under stirring and heating (100-110 .., 3 h) in DMSO (150 ml). Phenylacetylene (16.85 g, 0.165 mol) was added to the formed lithium oximate solution, temperature of the mixture was raised to 137-140 oC and the reaction mixture was stirred during 6 h. After cooling up to room temperature the reaction mixture was diluted with water and extracted with diethyl ether (50 ml x 5). The ether extracts were washed with water (50 ml x 3) and dried over K2CO3. The residue after removal of diethyl ether was distillated in vacuo (2 mm Hg) to remove acetophenone formed (9.94 g, 55%) and then rectified in fine vacuo (6.10-2 mm Hg) to give 4.70 g of unreacted oxime 1 (77% conversion) and 7.40 g of a fraction containing pyrrole 4 and side products (1H NMR). Recryctallization of this fraction from heptene afforded 5.59 g (17%) of 2,5-diphenyl-1H-pyrrole (4), beige crystals, m.p. 141-142 oC [ref.14 142 oC]; 1H NMR d 8.58 (br s, 1H, NH), 7.45 (m, 4H, .o), 7.30 (m, 4H, .m), 7.18 (m, 2H, ..), 6.57 (d, 4J = 2.5 Hz, 2H, H-3, H-4); 13. NMR d 133.2 (C-2, C-5), 132.6 (Ci), 129.0 (Cm), 126.2 (Cp), 123.9 (Co), 108.0 (C-3, C- 4); IR . 3457, 3058, 3022, 1943, 1868, 1803, 1735, 1605, 1579, 1486, 1459, 1380, 1333, 1314, 1275, 1186, 1156, 1076, 1052, 1028, 903, 783, 753, 691, 665, 510 cm-1. Anal. Calcd. for C16H13N: C, 87.64; H, 5.98; N, 6.38. Found: C, 87.86; H, 5.92; N, 6.20.
Analogously from oxime 1 (20.41 g, 0.151 mol), NaOH (6.04 g, 0.151 mol), phenylacetylene (16.85 g, 0.165 mol) (150 ml DMSO, 137-140 .., 6 h) was prepared 4.73 g (14%) of pyrrole 4, the oxime conversion was 80%.
Analogously from oxime 1 (20.41 g, 0.151 mol), KOH (8.47 g, 0.151 mol), phenylacetylene (16.85 g, 0.165 mol) (150 ml DMSO, 137-140 .., 6 h) was prepared 5.92 g (18%) of pyrrole 4, the oxime conversion was 69%.
