N-Acylated α-aminonitriles and their conversion into 5-aminooxazole, 5(4h)-oxazolone and 4(5h)-imidazolone derivatives

In contrast with the reaction of α-aminonitriles $\text{1}$a, the corresponding $\text{N}$-acylated α-aminonitriles $\text{1}$b-f and oxalyl chloride do not yield pyrazinone derivatives, but 5-aminooxazoles $\text{9}$-$\text{11}$ or 4(5$\text{H}$)-imidazolones $\text{12}$, the latter being converted in some cases into imidazo 2,1-$\text{a}$]isoquinoline-2,5,6(3$\text{H}$)-triones. Reactions of compounds $\text{1}$b-f and ethyl chlorooxoacetate provide evidence for a 5(4$\text{H}$)-iminooxazole intermediate $\text{7}$, which aromatizes to yield 5-aminooxazoles $\text{9}$-$\text{11}$; however, unaromatizable īntermediates of type $\text{7}$ - isolable as 5(4$\text{H}$)y-oxazolones $\text{13}$ after hydrolysis - undergo a catalyzed Dimroth-type rearrangement to give imidazolone derivatives $\text{12}$.