The N,O-bridged sesquinorbornadienes: a testing ground for establishing the superiority of N-Z pyrrole over furan as a dienofuge in retro-Diels–Alder reactions
✍ Scribed by Ronald N Warrener; Davor Margetic; Guangxing Sun
- Book ID
- 104230731
- Publisher
- Elsevier Science
- Year
- 2001
- Tongue
- French
- Weight
- 68 KB
- Volume
- 42
- Category
- Article
- ISSN
- 0040-4039
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✦ Synopsis
N-R pyrroles (R=H, Z, COPh but not Bn, TMS) 6 add selectively at rt to the substituted p-bond of 2,3-bis(trifluoromethyl)-7-oxanorbornadiene 7 under high pressure (14 kbar) to form exclusively the syn-facial N,O-sesquinorbornadienes 8; at higher temperatures the thermodynamic stereoisomers 10,11 are produced by cycloreversion and reaction at the unsubstituted p-bond. The exclusive loss of N-Z pyrrole from the N-Z derivative of 8 demonstrated the superior dienofugacity of N-Z pyrrole over furan; kinetic studies showed that the activation energy for this fragmentation was 34.7 kcal mol -1 . This selectivity is in accord with theory (AM1, ab initio).