Reactions of Nontautomeric Pyrazinones

Only a few of the recently reported reactions of fixed pyrazinones directly affect the oxo substituent. These and other reactions are illustrated in the following examples  

I -Bcnzyl-6-isobutyl-4-/ mcthoxybcnzyl-3,6-dihydro-2,5(l//,4//)-pyrazinedione (193) gave 1-bcnzyl-6-isobutyl-3,6-dihydro-2,5(l//,4//)-pyrazincdione (194) 

Isopropyl 4-benzyl-2,5-dioxo-6-(2,4,5-trimethoxy-3-methylbenzyl)-3-(2, 4,5-trimethoxy-3-methylbenzylidene)-l-piperazinecarboxylate (195) gave isopropyl 4-benzyl-2-hydroxy-5-oxo-6-(2,4,5-trimethoxy-3-methylbezyl)-3-(2,5-trimethoxy-3-methylbenzylidene)-l-piperazinecarboxylate (196) [LiAl(OBu )3H, THF, 0°C, 1 h 69%] also related esters likewise.292 

Note Like tautomeric pyrazinones (Section 5.1.2.1), nontautomeric pyrazinones undergo thiation easily. 

Irradiation of the light-sensitive crystal form of 1-methyl-5,6-diphenyl-2(l//)-pyrazinone (202) in the solid state gave the, sv -f ram-cyclodimer (203) (20°C, 4 h 86%) 1417 The anti-trans structure first proposed1417 was revised575 in light of an X-ray analysis.60 Also other examples.1327 

In contrast, l-benzyl-6-m-methoxybenzyl-2(l//)-pyrazinone gave only 6-m-mcihoxybcnzyl-2(l//)-pyrazinone on reductive debenzylation (liquid NHj—THF, Na 49%).  

Isopropyl 4-benzyl-2,5-dioxo-6-(2,4,5-trimethoxy-3-methylbenzyl)-3-(2, 4,5-trimethoxy- 3 -me thy Ibenzy lidene) -1 -piperazinecarboxy late (195) gave 

1-Methyl-5,6-diphenyl-2(lff)-pyrazinone (197, X = O gave 1-mclhy 1-5,6-diphenyl-2(l//)-pyrazinethione (197, X = S) (Lawesson s reagent, PhH, reflux, 1 h 91%)  

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