A practical and efficient protocol has been developed to realize the catalytic rearrangement of allyl but-3-enoate to heptadienoic acids in NaHCO3 saturated water, in the presence of catalytic amounts of a rhodium(l) complex, containing olefin, diene or phosphine ligands. The reaction mainly affords the sodium salt of E-2,6-heptadienoic acid, with high catalytic efficiency (3600 TON). A reaction scheme of the process is proposed. The reaction course differs from that observed in organic solvents, where E-3,6-heptadienoic acid is formed predominantly. (c) 2007 Elsevier B.V. All rights reserved.