A mild, green and extra activator‐free synthesis of allylic sulfones from non‐derivatized allylic alcohols and sulfinic acids was developed and only the easily‐available Pd(PPh3)4 was used as the catalyst. This new method could be easily scaled up to gram scale, affording the target allylic sulfones in a nearly quantitative yield with water as the sole by‐product. Mechanism studies both by various NMR techniques and by theoretical calculations suggested two reaction pathways may be involved in the reaction, which are dependent on the reaction media, that is, an eight‐membered ring binding species may be formed in aqueous media between allylic alcohol, sulfinic acid and water, while a six‐membered ring binding species may be formed in common aprotic organic solvent between allylic alcohol and sulfinic acid. Both binding species may be accounted for the efficient activation of allylic alcohols via hydrogen bonding.

A dehydrative cross coupling of ketone-stabilized phosphorus ylides with the readily available allylic alcohols followed by an one-pot Wittig reaction is developed. A range of functional 1,4-dienes could be obtained in 52%～95% isolated yields in the presence of 5 mol% Pd(PPh 3) 4 and 20 mol% B(OH) 3. The same method can be extended to ester or nitrile-stabilized phosphorus ylides, affording the corresponding 1,4-dienes in moderate yields. Keywords stabilized phosphorus ylides; allylic alcohols; dehydrative cross couplings; palladium catalysis