Title
Syntheses and some chemistry of 1,2- and 1,1-bis(2-pyrrolyl)ethenes
Document Type
Article
Publication Date
11-29-1996
Abstract
trans-1,2-Bis(2-pyrrolyl)ethenes (e.g. 18-20) are prepared by McMurry-type reductive coupling of the corresponding 2-formylpyrroles. The isomeric 1,1-bis(2-pyrrolyl)ethenes (e.g. 24) are prepared as a minor byproduct in the reaction of 2-unsubstituted pyrroles (e.g. 22) with acetic anhydride under Friedel-Crafts conditions; the major product, as expected is the 2-acetylpyrrole 23. However, 5-(chloromethyl)dipyrromethanes (e.g. 35) can be obtained in high yield by reaction of 2-unsubstituted pyrroles 22 with chloroacetaldehyde diethyl acetal. Base-catalyzed elimination of HCl from 35 affords the 1,1-bis(2-pyrrolyl)ethene 24 along with the trans- and cis-1,2-bis(2-pyrrolyl)-ethenes 18 and 36, respectively. Conditions are optimized to afford a 66% yield of the 1,1-bis(2-pyrrolyl)ethene 24. In neutral organic solvents, 1,1-bis(2-pyrrolyl)ethenes exist in the ethene tautomeric form 2, rather than as the corresponding 5-methyldipyrromethene isomer 3; however, under acidic conditions, the 5-methyldipyrromethene salt 38 is observed, and the 5-methyl group undergoes acid-catalyzed exchange in deuterated solvents. 1,1-Bis(2-pyrrolyl)ethenes (e.g. 24) undergo standard chemistry, such as catalytic hydrogenation (Adams catalyst) of the alkene bond (to give 5-methyldipyrromethane 44), Vilsmeier formylation [to give 2-formyl-1,1-bis(2-pyrrolyl)-ethene 57], and reaction with Eschenmoser's salt (N,N-dimethyl(methylene)ammonium iodide) [to give 2-((N,N-dimethylamino)methyl)-1,1-bis(2-pyrrolyl)ethene 59]. Both the 5-methyldipyrromethane-1,9-dicarboxylic acid 45 and the 1,1-bis(5-carboxy-3,4-dimethyl-2-pyrrolyl)ethene 53 react with the 1,9-diformyldipyrromethane 46, under standard MacDonald conditions, to give 3,5,8-trimethyldeuteroporphyrin IX dimethyl ester 47.
Publication Source (Journal or Book title)
Journal of Organic Chemistry
First Page
8508
Last Page
8517
Recommended Citation
Xie, H., Lee, D., Wallace, D., Senge, M., & Smith, K. (1996). Syntheses and some chemistry of 1,2- and 1,1-bis(2-pyrrolyl)ethenes. Journal of Organic Chemistry, 61 (24), 8508-8517. https://doi.org/10.1021/jo961582z