4-Pyridone ring

It was shown in the same article that the decarboxylation could also be performed by conventional heating but then copper cyanide was required and a mixture of saturated and imsaturated 2-pyridones 65 and 66 was obtained in a ratio of 1 10 (Fig. 10). A tentative mechanism was suggested for the reagent-free MAOS method where the carbonyl in the 2-pyridone ring is supposed to assist in the decarboxylation yielding an yUde 67 (Fig. 11). The decarboxylated bicyclic 2-pyridone 68 is thereafter obtained after protonation by the solvent. In agreement with the mechanistic suggestion, it was shown that a selective deuteration occurred when deuterated dimethyl sulfoxide (DMSO-de) was used as solvent. 

Hence, microwave irradiation in DMA for 12 min at 120 °C or 30 min at 140 °C, depending on the substrate, resulted in 20 or 21 in 90-96% yields, compared to yields around 50% and a 24 h reaction time for conventional heating. As can be seen in Eq. 2 in Fig. 5, two possibilities exist to connect the heteroaryl bromide part with the five-membered heterocycle (indicated by a and fi. Table 2) that results in a six-membered 2-pyridone ring. Still, a very high selectivity was obtained yielding the 2-pyridones 21, in which the new bond had been introduced at Ca. It should be noted that the obtained structures 20 and 21 represent heterocyclic derivatives of 2-quinolones rather than true 2-quinolones. 

The same group subsequently described the rapid functionalization of the bicyclic 2-pyridone ring, in particular various aminomethylation pathways (Scheme 6.217)... 

A 2-pyridone ring can be a building block for the synthesis of isoquinoline derivatives by acting as a dienophile in a Diels-Alder reaction. An electron-withdrawing group at C-4 is necessary for reaction with various substituted 1,3-butadienes (Equation 109) <2000CPB1814>. 

The mechanism of ring formation from monoalkyne and heterocumulenes, catalysed by Ni(0) complexes, Lx Ni(0), has been proposed to involve one-step cycloaddition scheme (10) [103] and scheme (11) [104, 105] show the formation of the 2-pyrone ring in the alkyne reaction with carbon dioxide and the 2-pyridone ring in the alkyne reaction with isocyanate respectively ... 

A similar approach has been used for the synthesis of 3-lH-pyrazolo[3,4-fc]pyridyl-indole ° and 2-aminochromene libraries, the latter being performed solvent free using a clay as a support and base. In addition, a library of over 100 derivatized substituted 2-pyridones (21 x 5 members) has been prepared by the reaction of 1,3-cyclohexane-diones, dimethylformamide dimethylacetal, and various cyanoacetamides (Scheme 4.10). The outcome of the reaction could be controlled to furnish different products by changing the basicity of the medium to involve either the amide or nitrile functionality of the cyanoacetamide substrate during the 2-pyridone ring-formation step. 

Lithium tetrahydroaluminatelaluminum chloride 1,2,3,6-Tetrahydropyridine from 2-pyridone ring s. 26, 63... 

N-Condensed 2-pyridone ring from carboxylic acid chlorides... 

Pyridone ring s. Carbostyrils 4-Pyridone ring, 2,3-dihydro-, N-condensed 21, 820 2-Pyridones... 

Ring closure with cyanocarboxylic acid amides 6-Amino-2-pyridone ring... 

Pyridone ring from 4-hydroxythiazoIium betaines via intramolecular 1,3-dipolar cycloaddition... 

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