An alkyl side-chain on an alfa or gamma-carbon of a N-heterocycle is subject to varying degrees of stabilisation by interaction with the ring. The resulting aninon (an enaminate) is stabilized in much the same way as a conjugated enolate. The most favourable situation is the alfa or gamma-carbon of a pyridine. The pKa data available ( 34 for a 2-methylpyridine, 27.5 for a 4-methylquinoline) show that the acidity is not so far from typical ketone alfa-deprotonation (pKa about 20).
A very attractive reactivity option consist on a prior electrophilic addition to the nitrogen, which acidifies further the side-chain H and enhances formation of enaminate and its nucleophilia. For a nice example see Chem.Lett., 1984, 1591.
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