A Convenient Route to 3-Pyrroline Utilizing the Delépine Reaction
Svante Brandänge*, Benito Rodriguez
*Department of Organic Chemistry, Arrhenius Laboratory, University of
Stockholm, S-10691 Stockholm, Sweden, Email: svante
organ.su.se
S. Brandänge, B. Rodriquez, Synthesis, 1988, 347-348.
DOI: 10.1055/s-1988-27571
Abstract
3-Pyrroline has been prepared from (Z)-1,4-dichloro-2-butene in three steps in an overall yield of 74%. The Delépine Reaction permitted the monoamination of the substrate in practically quantitative yields. The subsequent ring-closing reaction was less efficient.
Details
The document describes a convenient synthesis route for 3-pyrroline (2,5-dihydro-1H-pyrrole) from (Z)-1,4-dichloro-2-butene (1) using the Delépine reaction. The process involves three main steps:
- Reaction of 1 with hexamethylenetetramine in refluxing chloroform to produce (Z)-4-chloro-2-butenyl-1-azonia-3,5,7-triazatricyclo[3.3.1.1]decane chloride (2) in nearly quantitative yield.
- Conversion of 2 to (Z)-4-chloro-2-butenylammonium chloride (3) by treatment with hydrochloric acid in ethanol.
- Ring-closing of 3 with potassium carbonate in ethanol followed by deprotonation with pentaethylenehexamine to yield 3-pyrroline (4) with a final purity of 99% after distillation.
The overall yield of 3-pyrroline from the starting material is 74%. The document also mentions that separation of 3-pyrroline from pyrrolidine by crystallization or distillation is challenging due to their close boiling points and significant losses. The described method offers an improved and practical approach to synthesizing 3-pyrroline, overcoming the limitations of previous methods that were lengthy or had low yields. The work was supported by the Swedish Natural Science Research Council and involved detailed NMR and GC analysis to confirm the purity and structure of the compounds.
Key Words
Delépine Reaction, Allylamines, 3-Pyrrolines
ID: J66-Y1988-080
