SYNTHESIS OF SYMMETRICAL 2,2',4,4'-TETRASUBSTITUTED [4,4'-BIOXAZOL]-5,5'(4H,4'H)-DIONES AND THEIR REACTIONS WITH SOME NUCLEOPHILES

Several symmetrical trasubstituted[4,4'-bioxazole]-5,5'(4H,4'H)-diones 1a-f were obtained by dehydrodimerization of 5(4H)-oxazolones 2a-f. ? he configurations of four were established; one by X-ray crystallograp hy rac-1c, and three rac-1a, meso-la and rac-1b by H-1 nmr spectroscop y of their derivatives. Upon being heated, the bioxazolones isomerized , presumably by breakage of the 4,4'carbon-carbon bond to form free ra dicals followed by their recombination. The results of a crossover exp eriment were consistent with a radical nature for this isomerization r eaction. Treatment of three of the bioxazolones rac-1a, meso-la and ra c-1c with methanol and amine nucleophiles led to ester and amide deriv atives 7-11 of alpha,alpha'-dehydrodimeric amino acids.