Synthesis of dysideaproline E using organocatalysisElectronic supplementary information (ESI) available: Determination of the enantiopurity of acid 8; NMR spectra of 7, 8, 18, 20 and dysideaproline E 5. See DOI: 10.1039/c0ob00617c

( S )-4,4-Dichloro-3-methylbutanoic acid was prepared in 51% overall yield from commercially available starting materials using an organocatalytic transfer hydrogenation to 4,4-dichloro-3-methylbut-2-enal in the key step. The ( S )-dichloro acid was used as an intermediate in the first total synthesis of dysideaproline E and a diastereomer confirming the structure of the natural product. ( S )-4,4-Dichloro-3-methylbutanoic acid was prepared using an organocatalytic transfer hydrogenation of 4,4-dichloro-3-methylbut-2-enal as the key step then used in the first total synthesis of the marine natural product dysideaproline E.