| Autor: |
Kollenz, Gert, Holzer, Susanne, Kappe, C. Oliver, Dalvi, Turkaram S., Fabian, Walter M. F., Sterk, Heinz, Wong, Ming Wah, Wentrup, Curt |
| Zdroj: |
European Journal of Organic Chemistry; April 2001, Vol. 2001 Issue: 7 p1315-1322, 8p |
| Abstrakt: |
Treatment of dipivaloylketene 1 and its dimers 2 and 3 with 4-(dimethylamino)pyridine (DMAP) in acetonitrile affords the α-oxoketene-pyridine zwitterion 4 as a pale yellow solid. This is the first example of a stable zwitterion obtained from a true α-oxoketene. In anhydrous solution at room temp., compound 4 largely cleaves into the reactants 1 and DMAP. At −60 °C the equilibrium is shifted entirely towards the zwitterion 4, as shown by 13C NMR measurements. Calculations using density functional theory (B3LYP/6−311+G**) are in excellent agreement with the formation and relative stability of 4. 15N labelling experiments demonstrate that the ring nitrogen atom of DMAP is involved in generating the new zwitterionic C−N bond. Reactions of 4 with NH and OH nucleophiles in solution afforded the corresponding dipivaloyl acetic acid derivatives 6 and 7, whereas acetone or benzylidene aniline undergo cycloaddition reactions of the hetero-Diels−Alder type. |
| Databáze: |
Supplemental Index |
| Externí odkaz: |
|
Plný text