(R)-2-(carboxymethyl)-5-oxo-2,5-dihydro-2-furoate + H(+) = (4,5-dihydro-5-oxofuran-2-yl)-acetate + CO2 Aromatic compound metabolism; beta-ketoadipate pathway; 5-oxo-4,5-dihydro-2-furylacetate from 3-carboxy-cis,cis-muconate: step 2/2.