G. Kollenz, Susanne Holzer, C. Kappe
Apr 1, 2001
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0
Influential Citations
15
Citations
Journal
European Journal of Organic Chemistry
Abstract
Treatment of dipivaloylketene 1 and its dimers 2 and 3 with 4-(dimethylamino)pyridine (DMAP) in acetonitrile affords the alpha -oxoketene-pyridine zwitterion 4 as a pale yellow solid. This is the first example of a stable zwitterion obtained from a true alpha -oxoketene. In anhydrous solution at room temp., compound 4 largely cleaves into the reactants 1 and DMAP. At -60 degreesC the equilibrium is shifted entirely towards the zwitterion 4, as shown by C-13 NMR measurements. Calculations using density functional theory (B3LYP/6-311+G**) are in excellent agreement with the formation and relative stability of 4. N-15 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.