Synthetic studies on indole alkaloids. VII. Effect of the piperidine ring substitution on intramolecular KtBuO/BF3.Et2O cyclization of N-(2-hydroxyethyl)-2-[1-(phenylsulfonyl)-3-indolyl]piperidines
✍ Scribed by A. Diez; C. Villa; M. Rubiralta
- Book ID
- 104205025
- Publisher
- Elsevier Science
- Year
- 1993
- Tongue
- French
- Weight
- 752 KB
- Volume
- 49
- Category
- Article
- ISSN
- 0040-4020
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✦ Synopsis
3,3-Disubstituted N-(2-hydroxyethyl)-2-[ 1 -(phenylsulfonyl)-3-indolyll-piperidine 4 shows a particular reactivity in front of KtBuO/BFs.EtaO: the intermediate spiroindolenine 15 evolves to a tryptophylpiperidinium salt, which undergoes a Wagner-Meerwein rearrangement followed by a proton elimination to yield the 2,3-disubstituted Ktryptophylpiperidine-3-acrylates 19. In connection with our studies2 on the synthesis of fburnea indole alkaloids3 we have recently described the preparation of 1 -ethylindolo[2,3-alquinolizidine 1, through our usual method to obtain indolo[2,3-alquinolizidin-2-ones, i.e., by KtBuO intramolecular cyclization of protected N-(2-hydroxyethyl)-2-[1-(phenylsulfonyl)indolyl]-4-piperidones (3) followed by a BFs.Et20 induced rearrangement of the intermediate spiroindolenine (Scheme 1).4 We report now our studies on the preparation of l-ethyl-l-(methoxycarbonylmethyl)indolo[2,3-alquinolizidin-2-one (2) from the appropriate hydroxyethylpiperidine 4. With this purpose, our f/rst aim was to obtain 2-(3-indolyl)piperidine 4, .which was obtained as indicated in Scheme 2, by condensation of l-(phenylsuIfonyl)indoIe-3carbaldehyde (11)s with 2. R = CH2C02Me Szkntays intermediate