Heterocycles in asymmetric synthesis. Part 1. Construction of the chiral building blocks for enantioselective alkaloid synthesis via an asymmetric intramolecular Michael reaction
- 1 January 1992
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 1
- No. 4,p. 509-516
- https://doi.org/10.1039/p19920000509
Abstract
The asymmetric intramolecular Michael reaction of acyclic compounds ethyl (E)-4-[benzyl-(3-oxobutyl)amino]but-2-enoate 9, and ethyl (E)-5-[benzyl-(3-oxobutyl)amino]pent-2-enoate 10 was investigated under a variety of conditions, and the pyrrolidine ethyl (4-acetyl-1-benzylpyrrolidin-3-yl)acetate 11 and piperidine ethyl (3-acetyl-1-benzylpiperidin-4-yl)acetate 12, versatile chiral building blocks for alkaloid synthesis, were obtained in moderato to excellent optical yield. Cyclization of the aforementioned but- and pent-2-enoate using (R)-1-phenylethylamine in THF in the presence of molecular sieves 5 Å gave tha (+)-pyrrolidine derivative (+)-11 and the (–)-piperidine dsrivative (–)-12 in 60 and 90% ee., respectively. When (S)-1-phenylethylamine was used, pyrrolidine (–)-11 and piperidine derivatives (+)-12 Were obtained in similar optical yields, respectively. The ee of (–)-and (+)-piperidine derivatives increased up to 98% upon recrystallization of their hydrobromide salts.Keywords
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