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Title: Preparation and chemistry of an unexpectedly stable α-oxoketene-pyridine zwitterion, 2,2-bis(tert-butylcarbonyl)-1-[4-(dimethylamino)pyridinio]ethen-1-olate
Authors: Kollenz, G.
Holzer, S.
Kappe, C.O.
Dalvi, T.S.
Fabian, W.M.F.
Sterk, H.
Wong, M.W. 
Wentrup, C.
Keywords: Ab initio calculations
Nitrogen heterocycles
Issue Date: Apr-2001
Source: Kollenz, G.,Holzer, S.,Kappe, C.O.,Dalvi, T.S.,Fabian, W.M.F.,Sterk, H.,Wong, M.W.,Wentrup, C. (2001-04). Preparation and chemistry of an unexpectedly stable α-oxoketene-pyridine zwitterion, 2,2-bis(tert-butylcarbonyl)-1-[4-(dimethylamino)pyridinio]ethen-1-olate. European Journal of Organic Chemistry (7) : 1315-1322. ScholarBank@NUS Repository.
Abstract: 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.
Source Title: European Journal of Organic Chemistry
ISSN: 1434193X
Appears in Collections:Staff Publications

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