Synthesis of Symmetrical 2,2′,4,4′-Tetrasubstituted[4,4′-bioxazole]-5,5′(4H, 4′H)-diones and their Reactions with some Nucleophiles

Article abstract of DOI:10.1002/jhet.5570350210

Several symmetrical 2,2′,4,4′-tetrasubslituted[4,4′-bioxazole]-5,5′(4H, 4′H)-diones 1a-f were obtained by dehydrodimerization of 5(4H)-oxazolones 2a-f. The configurations of four were established; one by X-ray crystallography rac-1c, and three rac-1a, meso-1a and rac-1b by ¹H nmr spectroscopy of their derivatives. Upon being heated, the bioxazolones isomerized, presumably by breakage of the 4,4′-carbon-carbon bond to form free radicals followed by their recombination. The results of a crossover experiment were consistent with a radical nature for this isomerization reaction. Treatment of three of the bioxazolones rac-1a, mew-1a and rac-1c with methanol and amine nucleophiles led to ester and amide derivatives 7-11 of α,α′-dehydrodimeric amino acids.