Rh₂(OAc)₄ Catalyzed Wittig-Type Olefination: A Facile Access to Alkylidene and Arylidene Malonates

In the presence of triphenylarsine and catalytic amount of Rh₂(OAc)₄, one pot reactions with carbonyl compounds and dimethyl diazomalonate give the corresponding alkylidene and arylidene malonates in moderate to excellent yields (59%~99%). The scope of the carbonyl compounds covered a broad range, including aromatic and aliphatic aldehydes and ketone. The reaction was easily scaled up to gram scale with 0.5 mol% rhodium catalyst loading. The preliminary mechanistic studies showed that the olefination proceeded via a rhodium-carbene transformed arsonium ylide pathway.