The first synthesis of phosphonoacrolein. Application to Diels-Alder reaction as heterodiene

The first synthesis of phosphonoacrolein 3 was made in quantitative yield by acidic treatment of β-ethoxy-α-(methoxymethyl)vinylphosphonate 2, derived from a β-ethoxy-α-phosphonovinyl anion and MOMCl. The phosphonoacrolein 3 easily underwent a hetero-Diels−Alder reaction with electron-rich alkenes 4a−f or alkynes 9a−c under mild conditions, and phosphono-substituted pyrans 5a−d, 6e,f or pyranopyrans 11a−c were obtained in good to excellent yields. The reaction of 3 with cyclopentadiene and cyclohexadiene led to mixtures of [2 + 4] and [4 + 2] cycloadducts 7a, 8a and 7b, 8b in modest yields. The cycloaddition reaction between 3 and pyranopyran 13 or dibromocarbene and 13 resulted in [4 + 2] or [2 + 1] cycloadducts 14 or 15 in good yields.