New Morita-Baylis-Hillman (MBH) phosphonium salts from alcohols to the synthesis of 2-alkenyl- and 2-alkylidenecyclohexenones

Most of synthetic methods for 2- and 3-cyclohexenone derivatives start from limited substrates and therefore their efficiency still limited. In this paper, we report a general synthetic approach for such derivatives using MBH adducts, as substrates easily synthesized under standard conditions. For this purpose, a one-pot conversion of MBH alcohols into the corresponding phosphonium salts is carried out in high yields using PPh3 and an aqueous solution of HBr (48%), both at room temperature. Following purification and characterization of the title products, their further treatment at room temperature with either RCHO/tBuOK or only tBuOK, as the base, yields the corresponding 2-alkenyl- and 2-alkylidenecyclohexenones in good yields through Wittig olefinations or δ-elimination reactions of PPh3.HBr.