Pyrrolidine as a common contaminant of Δ3-pyrroline: Correct structure of the product from isatin and Δ3-pyrroline

Neurotoxicity studies with the monoamine oxidase B substrate 1-methyl-3-phenyl-3-pyrroline

“…The 1-methyl-3-(4-chlorophenyl)pyrrole intermediate was converted to the corresponding 1-methyl-3-(4-chlorophenyl)-3-pyrroline (4b) by partial reduction with zinc and hydrochloric acid (Williams and Lawson, 1998;Andrews and McElvain, 1929) in an overall yield of 31.9%. In our experience 3-pyrrolines prepared in this manner are often contaminated with what we believe is the corresponding pyrrolidinyl derivatives (Hudson and Robertson, 1967) in amounts ranging from approximately 10-25% as judged by 1 H NMR. We found that in selected instances (for example in the preparation of 4b, the pyrrolidinyl contaminant may be removed from the 3-pyrrolinyl free base under reduced pressure with slight heating (see Fig.…”

Five‐Membered Heterocycles: Pyrrole and Related Systems

“…It has long been established that reduction of pyrroles 290 with zinc in hydrochloric acid gives 2,5-dihydropyrroles (3-pyrrolines) 291 (Scheme 4.83) [442,443], although it was later found that the material obtained from the reduction of pyrrole itself is frequently contaminated with pyrrolidine, which is difficult to separate from the desired product [444]. The synthetic utility is further compromised by the fact that the formation of both cis and trans products occurs upon reduction of 2,5-dimethylpyrrole [445].…”

Oxidation and Reduction of the Pyrrole Ring

“…Early workers assumed that the Qtf H D5 H D7 H D8 H D9 A 3 -isomer was the sole product, but Evans (174) has shown that Δ 1 -and A 2 -pyrrolines may also be formed in low yield, e.g. (179) Similarly, 1-methylpyrrole is reduced* 173 ' 175) to l-methyl-A 3 -pyrroline, 1-methylpyrrolidine, and a dimeric compound, C 10 H 18 N 2 , the structure of which has been shown to be the (176) resulting from the reaction of the unreduced pyrrole with the A 3 -pyrroline. The formation of the A 2 -pyrroline may be rationalized in terms of the reduction of the ß-protonated pyrrole (D6).…”