Mechanistic Insight into the Formation of Tetraarylazadipyrromethenes

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• 作者：Marco Grossi ; Aniello Palma ; Shane O. McDonnell ; Michael J. Hall ; Dilip K. Rai ; Jimmy Muldoon ; Donal F. O鈥橲hea
• 刊名：The Journal of Organic Chemistry
• 出版年：2012
• 出版时间：October 19, 2012
• 年：2012
• 卷：77
• 期：20
• 页码：9304-9312
• 全文大小：481K
• 年卷期：v.77,no.20(October 19, 2012)
• ISSN：1520-6904

文摘

The tetraarylazadipyrromethene chromophore class has gained increasing attention in the past decade for a diverse set of scientific interests and applications. The most direct synthetic route available for their generation is heating of 4-nitro-1,3-diarylbutan-1-ones with an ammonium source in an alcohol solvent. Despite the practical simplicity, the reaction pathway(s) for these conversions are lengthy and unclear. To gain insight into the steps involved, ¹⁵N labeling experiments with MS and NMR analysis were utilized for conversion of 4-nitro-1,3-diphenylbutan-1-one 1 into tetraphenylazadipyrromethene 2 with ¹⁵NH₄OAc. To permit examination of later stages of the reaction sequence to 2, the ¹⁵N-labeled potential intermediate 3,5-diphenyl-1H-pyrrol-2-amine 10 was synthesized. A study of the dimerization pathway utilizing ¹⁵N-labeled 10 revealed an unprecedented nitrogen rearrangement in the final stages of the pathway involving a ring-opening/closing of a pyrrole ring. Utilizing ¹⁵N labeling experiments we have shown that 2,4-diphenylpyrrole 8 can also react under the reaction conditions with 3,5-diphenyl-2H-pyrrol-2-imine 7 (from oxidation of 10) to produce 2. Overall in the conversion of 1 into 2, two related pathways are ongoing concurrently; the first involves a dimerization of 3,5-diphenyl-2H-pyrrol-2-imine 7, and the other a reaction of 7 with 2,4-diphenylpyrrole 8.