Rhodium-catalyzed formation of stereocontrolled trisubstituted alkenes from Baylis-Hillman adducts.

Efficient and general conditions for the formation of stereodefined trisubstituted alkenes by using the rhodium-catalyzed reaction of unactivated Baylis-Hillman adducts with either organoboronic acids or potassium trifluoro(organo)borates are reported (see scheme).We report here efficient and general conditions for the formation of stereodefined trisubstituted alkenes using the rhodium-catalyzed reaction of unactivated Baylis-Hillman adducts with either organoboronic acids and potassium trifluoro(organo)borates. The use of the [{Rh(cod)OH}(2)] precursor gave very fast coupling reactions under low catalyst loading, very mild reaction conditions (from room temperature up to 50 degrees C) and without the need of additional phosphane ligands. Based on the new reaction conditions, the reaction, originally limited to Baylis-Hillman adducts derived from esters, could be extended to a large variety of Baylis-Hillman adducts, bearing either keto, cyano or amido functionalities. Moreover, the reaction of Baylis-Hillman adducts bearing esters functionality was improved and could be conducted at lower temperature using lower catalyst loading.