Tetramic acid 2.4- pyrrolidinedione

While in most reported cases the nucleophiles were amines, there were few examples involving heterocyclic nitrogens [40], alcoholic oxygens [27] or carbon nucleophiles [42, 43] too. Figure 4 shows a recent example of tandem Ugi-Dieckmann protocol [42]. Ugi convertible isocyanide 2, which requires a basic activation, was used, allowing a domino activation-cyclization of the intermediate 20 to give pyrrolidinediones (tetramic acids) 22. 

In 1901 Anschutz suggested the denotation tetramic acid for 1,5-dihydro-4-hydroxy-2-pyrrololone 2a, a tautomer of 2,4-pyrrolidinedione la (09LA55). By analogy to the term tetronic acid, denoting the lactone of 4-hydroxy-3-oxo-butanoic acid (60QR292), tetramic acid is used to name the lactam of 4-amino-3-oxo-butanoic acid. (See Fig. 1.)... 

However, it requires rather hindered /3-ketocstcrs to observe a significant drop in the yield of the arylation reaction with />-rn ethoxy phenyl lead triacetate 1 (Equation (3)).16 On the other hand, if the /3-dicarbonyl moiety is inserted into a cyclic structure, this difference disappears. For example, in the synthesis of functionalized tetramic acid derivatives, reaction of phenyllead triacetate 2 with the two five-membered cyclic pyrrolidinediones 3 and 4 afforded the diphenyl derivative 5 with a similar efficiency of the arylation step (Equations (4) and (5)).17... 

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