Abawt
-R&on of diketene with an exces of ammonia gives &aminocrotonamide (I), wbicb on b&ng is transformed into ~~~to~y~o~oto~de (IIb) wbicb bad been incomctly assigned tbe smxturc ~~3,~y~~,adimetlH-~p~do~~~de (I&I).*,' Hydnlysis of Sib w&b alkali gave ~~y~3~4p~idone cv) in a good yield. Structural assignmcnts of XIb are described. CHICK and WILSMORE~ reported in 1910 the reaction of diketene with ammonia to give acetoacetamide. When this reaction was carried out with an excess of ammonia, a white precipitate of acetoacetamide was converted into a yellow oil, which on heating was ~sfo~~ to a crystalline substance, m.p. 197', CsHBO,Ns (IQ They proposed the structure 4-amino-3,4-dihydro-4,6-dimethyi-lX-2-pyridone-5-carbamide (Ha) based on the following: (a) the elemental analysis and the mol. wt. determination, (b) hydrolysis of II with aq. alkali to give Camino3,4dihydro-4,6-dimethyl-2-p~done-~bo~~~ acid (Hr)t accompanied by the evolution of ~~rnol~~o~a. The authors quoted the self condensation reaction of acetoacetamides to give 4,6-~me~yl-lH-2-p~done-5~b~de
(IVa) as shown in Chart 1. Although the yellow oil could not be purified, they described it as consisting mainly of the nonisolated amide of @mGnocrotonic acid, CHsC(NHs):CHCONHs (I), from the analogy to the Claisen reaction .$ The structure 1;Ia was assigned to this compound (II).
Recently, L.&n* r+investigated this reaction and reported the same structure Ha.
In a previous pape# we reported that the structure of Claisen compound is not 4,6~e~yI-lH-Z-p~don~5~~de (I'Va) but 3-acetyl-4-amino-f-lH-2pyridone (IVb) and that in addition a good yield of 2,~e~yl4py~~done (V) was obtained. Accordingly, we re-investigated the structure II, because in part the structural assignment was incorrectly reported. In our present paper the preferred structure for II is shown to be ~~-a~~otony~o~roton~de
I&) and not the cyclic structure Ha proposed by Chick et o&l** According to the literature, 1 diketene was treated with excess ammonia to give a~toa~~de, which was ~~sfo~~ into a yellow oil. Heating of the yellow oil gave colorless crystals. Elemental analysis and mol. wt. determination established its * Part XII: T. Kate, H. Ytunanaka and T. Sbibata, C/fern. Pkrm. Buff, Jopm, to be published. t Tbe free acid III could not be isolated, but trcatmcnt of tbe reaction mixture with HNO, and AgNOs gave a ppt which WBS assumed to be tbe Ag salt of III.