2-Pyridone, reaction with dienophiles

The 0,0 -bis-f-butyldimethylsilyl derivative of an imide serves as an azadiene in reaction with dienophiles 2-pyridones are the resnlt, following desilylation. ° ... 

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>. 

Paquette4 considered that this reactive dienophile might undergo reaction with 2(1 H)-pyridone (1), a cisoid diene which has so far failed to undergo a Diels-Alder reaction, but the product (2) results from 1,2-addition of the amide proton to the triple bond. The N-methyl derivative of (1), which cannot undergo this type of reaction, gives rise only to black tars. 

The Diels-Alder reaction of 2-azadienes also benefits from the presence of an electron-donating substituent, to enhance the reactivity with electron-deficient dienophiles. Cycloaddition with alkynyl dienophiles and aromatization leads to substituted pyridines (3.54). Silyloxy-substituted 2-azadienes such as 68 are effective dienes and have been used to prepare substituted 2-pyridones and piperidones after methanolysis (3.55). Asymmetric hetero Diels-Alder reactions with the chiral Lewis acid catalyst 66 provide access to the piperidone products with very high enantioselectivity. ... 

The above results show that in reactions with arynes, pyrrolinediones act as synthetic equivalents of azadienes. One therefore wonders how they behave in reactions with other dienophiles. Is it possible to generalize the method described above to obtain a new synthetic route to pyridones and pyridines As a step in this direction, we have found that the pyrrolinedione 29b reacts rapidly with dimethyl acetylene dicarboxylate (DMAD) to give the emetine 42 in 75% yield (Scheme 14)(Ref. 21). 

Another approach towards monocyclic N-unsubstituted 2-pyridones is based on a solid-phase supported Diels-Alder reaction where a resin-bound 2(lH)-pyrazinone 9 is reacted with acetylenic dienophiles (Fig. 4) [43]. The initially formed cycloadduct then undergoes a retro Diels-Alder reaction and depending on the substitution pattern of the starting pyrazinone the reaction... 

Tetrahydro-2-pyridones are also produced by a [4+2] cycloaddition of l-aza-2-siloxydiene with simple dienes in a Lewis acid-catalyzed reaction (Equation 142) <2004S2222>. In an analogous manner, hydrazone derivatives have been in aza-[4+2] cycloadditions with reactive dienophiles which can be trapped with aldehydes to form highly functionalized piperidines (Scheme 88) <2004AGE2001, 2004JOC8429>. 

Krishnaiah, A. and Narsaiah, B. 2002. Studies on inverse electron demand hetero Diels-Alder reaction of perfluoroalkyl 2(1H) pyridones with different dienophiles under microwave irradiation. Journal of Fluorine Chemistry, 113 133-37. 

Phenylvinyl)-l,2-benzisothiazole 5, 5 -dioxides 115 (Ar = />-MeOC6H4) react in the presence of AICI3 acting as a dienophile with a second molecule of 115 to give the [4+2] dimer 182. 3-Methyl- and 3-chloro-l,2-benzisothiazole. y,.y-dioxides 112 (R = Me, Cl) react with Danishefsky s diene affording oxopyrido-benzisothiazoles 183 (R = Me) and 184, respectively. The fused pyridone 185 was formed from 3-methyl derivative 112 (R = Me), cinnamoyl chloride, and TEA by the way of a pericyclic reaction of the A -cinnamoyl intermediate <1996T3339>. 

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