New Synthesis of 2-Oxo-3-alkenylphosphonates and Hetero Diels–Alder Reactions with Vinyl Ethers Leading to 5-Substituted 2-Phosphiny 1-2-cyclohexen-1-ones

A new method of synthesizing phosphinyl-substituted enones, 2-oxo-3-alkenylphosphonates, is developed via the dianion of diethyl 2-oxopropylphosphonate. The enones serve as hetero dienes in thermal reactions with vinly ethers producing 2-alkoxy-6-(phosphinylmethyl)-3,4-dihydro-2H-pyrans. Acid-catalyzed cleavage of these cycloadducts is followed spontaneously by internal condensation furnishing 2-phosphinyl-2-cyclohexen-1-one derivatives.