Cyclization of 7-acyloxy-P-ketsesters of type I via acyl-oxygen ester fission in 100% sulfuric acid at 5" results in the formation of a-carbethoxy derivatives (11) of various tetronic acids (111) when the solutions are poured onto chopped ice. This procedure very probably proceeds with retention of configuration about the 7-carbon atom. Structural proof is provided for a tetronic acid (111, R1= t-Bu, Rz= Me) which fails to give a characteristic ...
