Abstract
The stereochemistry of bicyclic oxazepane-type intermediates for the synthesis of hydroxylated tropane alkaloids was determined by 1H NMR spectroscopy. Thermolysis of the 3α-tert-butyldimethylsiloxy-8-methyl-8-azabicyclo[3.2.1]oct-6-ene axial N-oxide diastereomer (1) in butyronitrile afforded the Meisenheimer rearrangement product, (1R*, 3S*, 5S*)-3-(tert-butyldimethylsiloxy)-9-methyl-8-oxa-9-azabicyclo[3.2.2]non-6- ene (2). NMR techniques have shown that this product experiences a conformational bias favoring occupancy of the bulky 3-tert-butyldimethylsiloxy substituent in an exo-disposed equatorial position on a boat oxazepane ring. It was found the tert-butyldimethylsiloxycycloheptenylamino fragment in 2 retained the same relative stereochemistry as ascribed to this moiety in the starting material 1. Removal of the bulky tert-butyldimethylsilyl protecting group afforded 5, having a less sterically demanding 3-hydroxy substituent, and resulted in an equilibrium between the boat and chair oxazepane ring conformations.
Original language | English |
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Pages (from-to) | 389-394 |
Number of pages | 6 |
Journal | Magnetic Resonance in Chemistry |
Volume | 35 |
Issue number | 6 |
DOIs | |
State | Published - 1 Jan 1997 |
Keywords
- Meisenheimer rearrangement
- NMR
- Physoperuvine
- Stereochemistry
- Tropane alkaloid
ASJC Scopus subject areas
- General Chemistry
- General Materials Science