Access to Stereodefined Trisubstituted Alkenes via Rhodium-Catalyzed 1,4-Addition of Potassium Trifluoro(organo)- borates to Baylis-Hillman Adducts

In the presence of a rhodium catalyst, unactivated Baylis–Hillman adducts reacted regioselectively with potassium trifluoro(organo)borates to afford stereodefined trisubstituted alkenes with good yields. This highly efficient reaction (aerobic conditions, low temperature, absence of added phosphane ligand) is believed to proceed via a 1,4‐addition/β‐hydroxy elimination mechanism.