Vinylic carbanions in synthesis. Novel syntheses of iso-gregatin B,iso-aspertetronin A and related O-methyl tetronic acids

Reaction between the octadienone (8) and the vinylic carbanion (6) derived from (5) leads, in one step, to the O-methyl tetronic acid (9). Metallation of (9), followed by treatment of the resulting α-vinylic carbanion with methyl acetate and with methyl $\text{E}$-butenoate then gives the acylated O-methyl tetronic acids (12) and (14) respectively which are shown to be enol ether isomers of the natural products gregatin B and aspertetronin A found in $\text{Aspergillus sp}$. and $\text{Cephalosporium gregatum}$.