[4+2] Cycloaddition of 1-aminodienes and 2-substituted vinylphosphonates: application to asymmetric synthesis of 3-amino-5-phosphono-1-cyclohexene derivatives

N-Butadienylsuccinimide (), iso-propyl N-butadienyl-(S)-pyroglutamate () and N-butadienyl-(R)-4-phenyloxazolidin-2-one () reacted with vinylphosphonates, vicinally-substituted () by electronwithdrawing groups (CO2Me, CN, COMe), to furnish [4+2] cycloadducts (, and ) in moderate to good yields (40–88%). The reactions were highly selective: regioselectivity of 95–100%, endoselectivity of 75–92% and facial selectivity of 80–95%. The major diastereoisomers were fully characterized by 1H and 13C NMR spectroscopy.